Hubble Galaxies

Too Fast, Too Furious: A Galaxy's Fatal Plunge

These images offer a dramatic look at a spiral galaxy like our Milky Way being ripped apart as it races at 4.5 million miles per hour through the heart of a distant cluster of galaxies. The images, taken over several wavelengths, provide evidence of the "galactic assault and battery," namely, gas being stripped from the doomed galaxy, called C153.

The composite photograph at left was made by combining the four images at right, taken in X-ray, radio, and visible wavelengths as well as the green light of oxygen gas. Astronomers studied the galaxy across several wavelengths to trace how stars, gas, and dust are being tossed around and torn from the fragile galaxy.

The composite image at left shows long streamers of gas flowing from the galaxy as it travels through the cluster, called Abell 2125. Hot gas from the cluster is stretching the galaxy's cooler gas into long streamers. Velocity measurements of several hundred galaxies in the cluster indicate that C153 is moving away from Earth within the cluster. The image, therefore, shows the streaking tail of "stripped gas." The image spans about 1 million light-years across. Abell 2125 is about 3 billion light-years away, on the boundary between the constellations Ursa Minor and Draco.

The visible-light image [above, right], taken by the Wide Field Planetary Camera 2 aboard NASA's Hubble Space Telescope, reveals intricate detail in the structure of stars and dust within C153. The galaxy exhibits evidence of a large-scale disturbance that has left its star-forming regions concentrated to one side of its disk and beyond. Dust features are twisted into chaotic patterns, obscuring any spiral pattern the galaxy once had.

X-ray emission [above, right], imaged by the Chandra X-ray Observatory, shows a gas tail extending from C153, which roughly matches the glowing gas tail observed in visible light. The temperature of the gas tail is cooler than the surrounding gas. This temperature difference is further evidence that gas is being "stripped" from the galaxy. The hotter gas is so diffuse that it cannot be seen in the image.

Radio observations [below, right] depict high-energy particles as they spiral through the galaxy's magnetic field, with some escaping in a perpendicular direction to the galaxy's disk. The particles probably came from an energetic black hole that was fueled by a collision between two galaxy clusters. This emission first marked C153 as unusual, leading scientists to conduct further observations.

The image [below, right], taken by the 4-meter Mayall telescope at Kitt Peak National Observatory, isolated the light from glowing oxygen gas. This view shows a tail forming as gas is pulled from the galaxy and stretched into long streamers that extends for about 200,000 light-years.

Credit: NASA, W. Keel (U Alabama), F. Owen (NRAO), M. Ledlow (Gemini Obs.), and D. Wang (U Mass.)

A Tale of Two Record-Breaking Galaxy Clusters

Looking back in time to when the universe was in its formative youth, the Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope captured these revealing images of two galaxy clusters.

The image at left shows mature galaxies in a massive cluster that existed when the cosmos was 5 billion years old. The cluster, called RDCS 1252.9-2927, is as massive as 300 trillion suns and is the most massive known cluster for its epoch. The Hubble image reveals the core of the cluster and is part of a much larger mosaic of the entire cluster. Dominating the core are a pair of large, reddish elliptical galaxies [near center of image]. Their red color indicates an older population of stars. Most of the stars are at least 1 billion years old. The two galaxies appear to be interacting and may eventually merge to form a larger galaxy that is comparable to the brightest galaxies seen in present-day clusters.

The red galaxies surrounding the central pair are also cluster members. The cluster probably contains many thousands of galaxies, but only about 50 can be seen in this image. The full Hubble mosaic reveals several hundred cluster members. Many of the other galaxies in the image, including several of the blue galaxies, are foreground galaxies. The color-composite image was assembled from observations taken between May and June 2002 by the ACS Wide Field Camera.

In the image at right, astronomers are seeing an embryonic cluster as it was when the universe was 1.5 billion years old. The young system, called TN J1338-1942, is the most distant known developing cluster, or proto-cluster. It is dominated by a massive "baby galaxy," the green object in the center with the blue circle around it. The galaxy is producing powerful radio emissions, and is the brightest galaxy in the proto-cluster. The green color indicates that the galaxy is emitting glowing hydrogen gas. Its clumpy appearance suggests that it is still in the process of forming. Smaller developing galaxies, marked by the blue circles, are scattered around the massive galaxy. The galaxy on the left of the massive galaxy is a foreground galaxy. The bright object in the upper half of the image is a foreground star. This color-composite image was assembled from observations taken between July 8 and 12, 2002 by the ACS Wide Field Camera

Credits for RDCS 1252: NASA, ESA, J. Blakeslee (Johns Hopkins University), M. Postman (Space Telescope Science Institute), and P. Rosati (European Southern Observatory)

Credits for TN J1338: NASA, ESA, G. Miley (Leiden Observatory), and R. Overzier (Leiden Observatory)

Swirling Galaxy Parents Generations of Stars in Its Center

The NASA/ESA Hubble Space Telescope has snapped a view of several star generations in the central region of the Whirlpool Galaxy (M51), a spiral region 23 million light-years from Earth in the constellation Canes Venatici (the Hunting Dogs).

The galaxy's massive center, the bright ball of light in the center of the photograph, is about 80 light-years across and has a brightness of about 100 million suns. Astronomers estimate that it is about 400 million years old and has a mass 40 million times larger than our Sun. The concentration of stars is about 5,000 times higher than in our solar neighborhood, the Milky Way Galaxy. We would see a continuously bright sky if we lived near the bright center.

The dark "y" across the center is a sign of dust absorption. The bright dot in the middle of the "y" has a brightness of about one million suns, but a size of less than five light-years. Its power and its tiny size suggest that we have located the elusive central black hole that produces powerful radio jets.

Surrounding the center is a much older stellar population that covers a region of about 1,500 light-years in diameter and is at least 8 billion years old, and may be as old as the Universe itself, about 13 billion years.

Further away, there is a "necklace" of very young star-forming regions, clusters of infant stars, younger than 10 million years, which are about 700 light-years away from the center. Normally, young stars are found thousands of light-years away.

Astronomers believe that stars in the central region were formed when a dwarf companion galaxy - which is not in the photograph - passed close to it, about 400 million years ago, stirring up dust and material for new star birth. The close encounter has been felt for a long time and is believed to be responsible also for the unusually high star formation activity in the bright necklace of young stars.

The color image was assembled from four exposures taken Jan. 15, 1995 with Wide Field Planetary Camera-2 in blue, green, and red wavelengths.

Credit: Nino Panagia (Space Telescope Science Institute and European Space Agency) and NASA

Hubble Probes the Violent Birth of Stars in Galaxy NGC 253

[Left]
An image of the spiral galaxy NGC 253, taken with a ground-based telescope. The galaxy is located about 8 million light-years away in the constellation Sculptor.

[Right]
This NASA Hubble Space Telescope image of the core of the nearest starburst spiral galaxy, NGC 253, reveals violent star formation within a region 1,000 light-years across. A starburst galaxy has an exceptionally high rate of star birth, first identified by its excess of infrared radiation from warm dust. Hubble's high resolution allows astronomers to quantify complex structures in the starburst core of the galaxy for the first time, including luminous star clusters, dust lanes which trace regions of dense gas and filaments of glowing gas. Hubble identifies several regions of intense star formation, which include a bright, super-compact star cluster. These observations confirm that stars are often born in dense clusters within starbursts, and that dense gas coexists with and obscures the starburst core. This image was taken with Hubble's Wide Field Planetary Camera 2 (in PC mode).

Left Credit: Jay Gallagher (University of Wisconsin-Madison), Alan Watson (Lowell Observatory, Flagstaff, AZ), and NASA

Right Credit: Carnegie Institution of Washington

The Coma Cluster of Galaxies as imaged by HST

Color Print of NGC 4881 and Part of the Surrounding Field

This photo mosaic, which shows a field of distant galaxies, is a computer enhanced reproduction of a picture taken 4 March 1994 with the repaired Hubble Space Telescope. It combines 16 exposures of 15 minutes each, taken through two filters (F555W and F814W) with the Wide Field Planetary Camera 2. The HST WFPC2 field is chevron-shaped, because it is a mosaic of images recorded with three Wide Field cameras and one higher resolution camera (Planetary Camera) in the upper left.

The brightest object in this picture is NGC 4881, approximately centered here in the Planetary Camera (the small quadrant). It is a 13th-magnitude elliptical galaxy in the outskirts of the Coma Cluster, a great cluster of galaxies more than 5 times farther away than the Virgo Cluster. The radical velocity (redshift) of NGC 4881, based on the Doppler displacement of lines in its spectrum, is about 7000 km/sec. Except for a 16th-magnitude Coma spiral at the right and a few foreground stars of the Milky Way, nearly everything else in this field lies far beyond the Coma Cluster. There is a fascinating assortment of background galaxies, including an apparent galaxian merger in progress.

Purpose: This HST-WFPC2 observation was made to explore the use the globular star clusters surrounding NGC 4881 as distance indicators for inferring the distance to the Coma Cluster. They are barely visible point sources in this reproduction. The distance to the Coma Cluster is an important cosmic yardstick for scaling the over all size of the universe, because Coma (unlike Virgo) is far enough away that regional departures from a smooth expansion of the universe should not be a major source of uncertainty if Coma is used for estimating the age and rate of expansion (the Hubble Constant).

The brightness distribution of globular clusters has been studied in a number of nearer galaxies. They are most numerous between -7 and -8 absolute magnitude. In the Milky Way they peak at -7.6 absolute magnitude. We must find that peak ("turnover") in NGC 4881 in order to judge the distance. Within statistical uncertainties, the number of globulars per magnitude in NGC 4881 increases down to our present threshold of 27.6 magnitude. We do not yet see evidence of the turnover in NGC 4881, which suggests that the Coma Cluster may be more than 100 megaparsecs away and that the Hubble Constant may therefore be less than 70 km/sec per megaparsec. The adding together of more exposures will evidently be needed to reach a fainter threshold and find the turnover. Though not yet definitive in itself, this exploratory observation of NGC 4881 shows that it is within the reach of HST to obtain a definitive globular-cluster distance to the Coma Cluster and an associated value of the Hubble Constant.

Credit: Hubble Space Telescope WFPC Team, NASA, STScI

M104, The Sombrero Galaxy as imaged by HST

Hubble Mosaic of the Majestic Sombrero Galaxy

NASA's Hubble Space Telescope has trained its razor-sharp eye on one of the universe's most stately and photogenic galaxies, the Sombrero galaxy, Messier 104 (M104). The galaxy's hallmark is a brilliant white, bulbous core encircled by the thick dust lanes comprising the spiral structure of the galaxy. As seen from Earth, the galaxy is tilted nearly edge-on. We view it from just six degrees south of its equatorial plane. This brilliant galaxy was named the Sombrero because of its resemblance to the broad rim and high-topped Mexican hat.

At a relatively bright magnitude of +8, M104 is just beyond the limit of naked-eye visibility and is easily seen through small telescopes. The Sombrero lies at the southern edge of the rich Virgo cluster of galaxies and is one of the most massive objects in that group, equivalent to 800 billion suns. The galaxy is 50,000 light-years across and is located 28 million light-years from Earth.

Hubble easily resolves M104's rich system of globular clusters, estimated to be nearly 2,000 in number — 10 times as many as orbit our Milky Way galaxy. The ages of the clusters are similar to the clusters in the Milky Way, ranging from 10-15 billion years old. Embedded in the bright core of M104 is a smaller disk, which is tilted relative to the large disk. X-ray emission suggests that there is material falling into the compact core, where a 1-billion-solar-mass black hole resides.

In the 19th century, some astronomers speculated that M104 was simply an edge-on disk of luminous gas surrounding a young star, which is prototypical of the genesis of our solar system. But in 1912, astronomer V. M. Slipher discovered that the hat-like object appeared to be rushing away from us at 700 miles per second. This enormous velocity offered some of the earliest clues that the Sombrero was really another galaxy, and that the universe was expanding in all directions.

The Hubble Heritage Team took these observations in May-June 2003 with the space telescope's Advanced Camera for Surveys. Images were taken in three filters (red, green, and blue) to yield a natural-color image. The team took six pictures of the galaxy and then stitched them together to create the final composite image. One of the largest Hubble mosaics ever assembled, this magnificent galaxy is nearly one-fifth the diameter of the full moon.

Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Celestial Composition

Amid a backdrop of far-off galaxies, the majestic dusty spiral, NGC 3370, looms in the foreground in this NASA Hubble Space Telescope image. Recent observations taken with the Advanced Camera for Surveys show intricate spiral arm structure spotted with hot areas of new star formation. But this galaxy is more than just a pretty face. Nearly 10 years earlier NGC 3370, in the constellation Leo, hosted a bright exploding star.
In November 1994, the light of a supernova in nearby NGC 3370 reached Earth. This stellar outburst briefly outshone all of the tens of billions of other stars in its galaxy. Although supernovae are common, with one exploding every few seconds somewhere in the universe, this one was special. Designated SN 1994ae, this supernova was one of the nearest and best observed supernovae since the advent of modern, digital detectors. It resides 98 million light-years (30 megaparsecs) from Earth. The supernova was also a member of a special subclass of supernovae, the type Ia, the best tool astronomers have to chart the growth rate of the expanding universe.
Recently, astronomers have compared nearby type Ia supernovae to more distant ones, determining that the universe is now accelerating in its expansion and is filled with mysterious "dark energy." Such measurements are akin to measuring the size of your room by stepping it off with your feet. However, a careful measurement of the length of your foot (to convert your measurements into inches or centimeters) is still needed to know the true size of your room. Similarly, astronomers must calibrate the true brightness of type Ia supernovae to measure the true size and expansion rate of the universe.
The very nearest type Ia supernovae, such as SN 1994ae, can be used to calibrate distance measurements in the universe, because other, fainter stars of known brightness can be observed in the same galaxy. These stellar "standard candles" are the Cepheid variable stars, which vary regularly in brightness with periods that are directly related to their intrinsic brightness, and thus allow the distance to the galaxy—and the supernova—to be determined directly. However, only the Hubble Space Telescope, equipped with its new Advanced Camera for Surveys, has the capability to resolve these individual Cepheids.
Adam Riess, an astronomer at Space Telescope Science Institute in Baltimore, Md., observed NGC 3370 a dozen times over the course of a month and has seen many Cepheid variables. Already he and his colleagues can see that these Cepheids are the most distant yet observed with Hubble. Because of their need to observe this galaxy with great frequency to record the variation of the Cepheids, the total exposure time for this galaxy is extremely long (about one full day), and the combined image provides one of the deepest views taken by Hubble. As a result, thousands of distant galaxies in the background are easily discernable.
Dr. Riess imaged NGC 3370 with Hubble in early 2003. His science only required looking at NGC 3370 in two filters that covered the visual and infrared portions of the spectrum. By teaming up with the Hubble Heritage Project, a third blue filter was added to the data to produce the composite three-color image that is shown.
Credit: NASA, The Hubble Heritage Team and A. Riess (STScI)

A deep view of the early universe as imaged by HST

Hubble's "Deep" View of Early Universe Helps Solve the Faint Blue Galaxy Mystery

One of the deepest images of the sky taken to date with NASA's Hubble Space Telescope reveals a population of faint blue galaxies which turn out to be the most common class of objects in the universe. Their distances are estimated to range from three to eight billion light-years, meaning that they were abundant when the universe was a fraction of its present age, but are rare or harder to find today because they have faded or self-destructed.

This picture, in combination with a series of images from the Hubble Space Telescope Medium Deep Survey that covers a larger area of sky, is allowing astronomers to solve the longstanding "faint blue galaxy mystery" by showing the true nature of these dim and remote objects. Deciphering the formation and evolution of these blue dwarf galaxies may provide new clues to understanding the process of galaxy evolution, including the formation of our Milky Way Galaxy.

Hubble's high resolution shows that most of these faint galaxies do not resemble elliptical and well-defined spiral galaxies that are common in the present universe. Instead, they have a wide variety of shapes suggesting that galaxy collisions and other interactions were more common in the past. The galaxies are blue because they are undergoing episodes of intense star-formation which produce a lot of young, hot, and blue stars.

This picture is a true-color image made from separate exposures taken in blue, green, and far-red light with the Wide Field and Planetary Camera 2. It required a total of 48 orbits around the Earth (amounting to roughly one day of exposure time) to make the observation and detect objects about four billion times fainter than the unaided eye can see (30th magnitude). The image resolution is about 0.06 arc seconds. The image covers a relatively small area of sky — only one tenth the diameter of the full moon — in the constellation Hercules.

Credit: Rogier Windhorst and Simon Driver (Arizona State University), Bill Keel (University of Alabama), and NASA

Deepest View of Space Yields Young Stars in Andromeda Halo

Relying on the deepest visible-light images ever taken in space, astronomers using NASA's Hubble Space Telescope (HST) have reliably measured the age of the spherical halo of stars surrounding the neighboring Andromeda galaxy (M31).
To their surprise, they have discovered that approximately one-third of the stars in Andromeda's halo formed only 6 to 8 billion years ago. That's a far cry from the 11-to-13 billion-year age of the stars in the Milky Way's halo.
Why the difference in halo ages? You might call it a tale of rich galaxy/poor galaxy. Apparently, M31 must have gone through a major "corporate merger" with another large galaxy, or a series of mergers with smaller galaxies, billions of years ago. Astronomers cannot yet tell whether this was one tumultuous event or a more continual acquisition of smaller galaxies. The newly discovered younger stars in Andromeda's halo are richer in heavier elements than the stars in our Milky Way's halo, or in most of the small dwarf galaxies that surround the Milky Way. Indeed the level of chemical enrichment seen in these younger stars is characteristic of relatively massive galaxies, containing at least a billion stars.
This suggests three possibilities: (1) Collisions destroyed the young disk of M31 and dispersed many of its stars into the halo; (2) a single collision destroyed a relatively massive invading galaxy and dispersed its stars and some of Andromeda's disk stars into the halo; and/or (3) many stars formed during the collision itself.
Astronomers say it will take more detailed observations to unravel the acquisition history of these early cataclysmic events. Located only 2.5 million light-years away, the magnificent Andromeda galaxy, visible as a naked-eye spindle of light in the autumn sky has long been considered a near twin to our Milky Way in terms of size, shape, and age. This new finding promises to offer new clues on how giant galaxies like M31 and our Milky Way formed by gravitationally shredding galaxies, like a cosmic Cuisinart, and then devouring them.
Dr. Tom Brown of the Space Telescope Science Institute (STScI) is reporting the findings today in Baltimore at the STScI May Symposium, "The Local Group as an Astrophysical Laboratory." His team used Hubble's Advanced Camera for Surveys (ACS) to peer into a small sample of the Andromeda halo for 120 Hubble orbits. This allowed for a study of the entire demographics of the halo population, down to its extremely faint stars.
Previously, telescopes could only see the bright giant stars in the halo population, but the population of "normal" stars like our own Sun was beyond our grasp, because such stars in M31 are so faint. The ACS is the first astronomical camera to combine ultra-sharp vision and sensitivity to ferret out M31's faint halo population.
An estimated 300,000 of these never-before-seen halo stars can be resolved, peppering Hubble's narrow sample of the halo population. Looking far beyond the halo stars, Hubble reveals thousands of background galaxies (down to 31st magnitude) billions of light-years away.
A large fraction of the background galaxies in the image also have peculiar shapes due to collisions. This reinforces the fact: we live in a vibrant and dynamic universe undergoing constant change.

Freewheeling Galaxies Collide in a Blaze of Star Birth

A dusty spiral galaxy appears to be rotating on edge, like a pinwheel, as it slides through the larger, bright galaxy NGC 1275, in this NASA Hubble Space Telescope image.

These images, taken with Hubble's Wide Field Planetary Camera 2 (WFPC2), show traces of spiral structure accompanied by dramatic dust lanes and bright blue regions that mark areas of active star formation. Detailed observations of NGC 1275 indicate that the dusty material belongs to a spiral system seen nearly edge-on in the foreground. The second galaxy, lying beyond the first, is actually a giant elliptical with peculiar faint spiral structure in its nucleus. These galaxies are believed to be colliding at over 6 million miles per hour.

NGC 1275 is about 235 million light-years away in the constellation Perseus. Embedded in the center of a large cluster of galaxies known as the Perseus Cluster, it is also known to emit a powerful signal at both X-ray and radio frequencies. The galaxy collision causes the gas and dust already existing in the central bright galaxy to swirl into the center of the object. The X-ray and radio emission indicates the probable existence of a black hole at the bright galaxy's center.

While the dark dusty material in the Hubble image falls inward, NGC 1275 displays intricate filamentary structures at a much larger scale outside the image. This is a typical feature of bright cluster galaxies. Additional observational evidence of strong interactions between at least two galaxies, and possibly a few smaller galaxies, includes the formation of new stars and large star clusters. Although similar in shape to the old globular clusters in the Milky Way galaxy, NGC 1275's clusters are much younger and contain 100,000 to a million stars each.

This image was created from archived blue and red Hubble WFPC2 data taken in 1995 by John Trauger (JPL) and Jon Holtzman (NMSU). The Hubble Heritage team, along with collaborators Megan Donahue, Jennifer Mack, and Mark Voit (STScI), took follow-up WFPC2 observations at infrared wavelengths in 2001 to help produce this full-color image.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Acknowledgment: M. Donahue (STScI) and J. Trauger (JPL)

Starry Bulges Yield Secrets to Galaxy Growth

NASA's Hubble Space Telescope is uncovering important new clues to a galaxy's birth and growth by peering into its heart — a bulge of millions of stars that resembles a bulbous center yolk in the middle of a disk of egg white.
Hubble astronomers are trying to solve the mystery of which came first: the stellar disk or the central bulge?
Two complementary surveys by independent teams of astronomers using Hubble show that the hubs of some galaxies formed early in the Universe, while others formed more slowly, across a long stretch of time.
Hubble confirms that the evolutionary paths of bulges and disks are connected. The central bulge stabilizes a galaxy's development and largely controls the ebb and flow of star birth in the core. The central bulge holds secrets as to how and when a galaxy formed. Before Hubble, astronomers had detailed information only about the complex core of our galaxy, which has a small bulge peppered with massive young star clusters and a telltale bar structure funneling gas to the center. Hubble allows astronomers to see bright star clusters, bars and other structures deep inside the bulges of other galaxies.
A group led by Reynier Peletier from the University of Nottingham, in the United Kingdom, has confirmed that the central bulges of more tightly wound spirals were all created at more or less the same time in the early universe.
A second team, led by C. Marcella Carollo of Columbia University in New York, surveyed galaxies that have small bulges and bar-like structures that bisect the nucleus like the slash across a no-smoking sign. They found that the bulges in these galaxies grew more recently, through markedly different processes happening within the galaxy's disk.
Both surveys used Hubble's precise resolution to peer into bulbous hubs of more than 200 neighboring galaxies, out to a distance of 100 million light-years. Using Hubble's visible-light and infrared cameras to penetrate deep into the cores of the galaxies, astronomers were able to untangle the stars' true colors — a measure of age — from their apparent colors, which are made redder by interstellar dust.
Peletier's team used Hubble to look into the center of 20 spiral galaxies that have large bulges. The team found that elliptical bulges of stars formed over a relatively brief period very early in the young universe. This could have happened through the collapse of a single cloud of hydrogen or merger of primeval star clusters.
"Apparently everywhere in the universe these intermediate-sized galaxies must have started forming early on," reports Peletier in a paper to be published in the Monthly Notices of the Royal Astronomical Society. "The bulges of early spiral galaxies are old, and at least the outer parts of their disks are considerably younger."
Carollo's team found that in a different class of spiral galaxy, a small bulge probably formed early on, but was later fed by gas flowing into the galaxy's core, likely along a bar-like structure caused by instabilities in the surrounding disk of stars. The gas fueled the birth of new stars, and the bulge inflated like a beach ball as brilliant star clusters populated the center.
Carollo's results, to be published in the Astrophysical Journal, show young and old stars in the bulge. The researchers say that these types of bulges can continue to grow in galaxies in the present universe, but it is unlikely that they will ever become as big as those giant bulges that formed when the universe was young.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

A Minuet of Galaxies

This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years.
The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object.
The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies.
HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes. The HST exposures of the winning target were then acquired in July 1999 by the Hubble Heritage Team and guest astronomers Sally Hunsberger (Lowell Observatory, Flagstaff, Arizona) and Jane Charlton (Pennsylvania State University). Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: S. Hunsberger (Lowell Obs.) and Jane Charlton (Pennsylvania State U.)

Hubble Resolves a Blaze of Stars in a Galaxy's Core

The central region of the small galaxy NGC 1705 blazes with the light of thousands of young and old stars in this image, taken by NASA's Hubble Space Telescope.
At 17 million light-years away, the individual stars of the dwarf irregular galaxy NGC 1705 are out of range of all but the sharp eyes of Hubble. NGC 1705 is an ideal laboratory to conduct investigations on star formation history. Young, blue, hot stars are strongly concentrated toward the galaxy's center, while older, red, cooler stars are more spread out. This galaxy has been forming new stars throughout its lifetime, but a burst of star-formation activity occurred as recently as 26 to 31 million years ago. This "starburst" is responsible for many of the young stars on the outskirts of the galaxy's core, as well as the central giant star cluster.
NGC 1705 is classified as a dwarf irregular because it is small and lacks any regular structure. Many astronomers now believe that dwarf galaxies, like NGC 1705, were the first systems to collapse and start forming stars in the early universe. They represent the building blocks from which more massive objects (spiral and elliptical galaxies) were later formed through mergers and accretion. Nearby small galaxies are thought to be the leftovers of the galaxy-formation process.
Dwarf irregulars are similar in many ways to very young galaxies, but they are much nearer and easier to study. These galaxies seem to have consumed only a tiny percentage of their reservoir of gas. Their stars have a much lower fraction of heavy elements than does the Sun. These are all indications that only a few generations of stars have formed there over time. Current star formation is taking place at a fairly high rate in starburst episodes. All these characteristics make dwarf irregular galaxies the ideal local analogues to young galaxies from the early universe. Understanding their evolution is extremely useful and sheds light on the many processes related to galaxy formation and evolution.
Dwarf irregulars play a key role in astronomers' attempts to unravel the history of galaxies in the early universe. These galaxies are probably best described as fairly old stellar systems whose chemical and physical properties can be ascribed to a process of slow evolution. The Hubble observations of the stars in NGC 1705 and other close irregulars have demonstrated that these galaxies are several billion years old. NGC 1705 could be as old as 13.5 billion years.
This image was taken in March 1999 and November 2000 by an international science team led by Monica Tosi at Italy's National Institute of Astrophysics (INAF) at the Osservatorio Astronomico di Bologna. Other team members include Alessandra Aloisi (JHU), Mark Clampin (STScI), Laura Greggio (INAF, Osservatorio Astronomico di Padova), Claus Leitherer and Antonella Nota (STScI). Hubble's Wide Field Planetary Camera 2 observed the galaxy in ultraviolet, blue, visible, and infrared light. Although not included in this image, NICMOS (Near Infrared Camera and Multi-Object Spectrometer) observations were also made of the galaxy's central core.
Image Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: M. Tosi (INAF, Osservatorio Astronomico di Bologna)

Scientists Find Faint Objects with Hubble that May Have Completed the Universe's 'Dark Ages'

Researchers at Arizona State University using NASA's Hubble Space Telescope believe they are seeing the conclusion of the cosmic epoch where the young galaxies started to shine in significant numbers. This marks a time when the so-called "Dark Ages" of the universe was completed, about 13 billion years ago. (Based on an estimate of 14 billion years for the current age of the universe.)

The arrows in this Hubble image indicate three of the thirty objects that the team discovered using Hubble's new Advanced Camera for Surveys (ACS). Astronomers believe that these numerous objects are faint young star-forming galaxies seen when the universe was seven times smaller than it is today (at redshifts of about 6) and less than a billion years old. This is right around the cosmic epoch where astronomers believe that radiation from hot stars in numerous young galaxies was converting the universe's cool hydrogen into a hot ionized gas.

The distances to the suspected young galaxies are believed to be so large given how red the observed objects are. This is interpreted as being caused by the enormous expansion of the universe since that early epoch. Almost all of the ultraviolet light from the young stars has been stretched (or redshifted) to far-red wavelengths. As a consequence, these three objects are only visible in the reddest of the two filters aboard the ACS.

The entire ACS field of view shows about thirty such faint red objects. This means nearly 8,000 such objects would fill a patch of sky no bigger than what is covered by holding your thumb at arm's length, the Arizona researchers estimate. They conclude that at least 400 million such objects filled in the entire universe at this cosmic epoch to the limit of this Hubble image. And, this is likely only the tip of the iceberg. NASA's planned 7-meter James Webb Space Telescope will see the entire population of these proto-galactic objects.

Credit: NASA, H.-J. Yan, R. Windhorst and S. Cohen (Arizona State University)

Giant Radio Jet Coming from Wrong Kind of Galaxy

Composite images showing the galaxy 0313-192, the first spiral galaxy known to be producing a giant radio-emitting jet. At left is a wide view of 0313-192 and its surroundings, as seen with the Advanced Camera for Surveys of the NASA Hubble Space Telescope (HST), in an image made in July 2002. The radio-emitting jet, as seen with the Very Large Array (VLA) at a wavelength of 20 centimeters, is overlaid, in red on the color image. The galaxy is seen edge-on. At right is a close-up of the HST image, with another red overlay from a higher-resolution, 3-centimeter VLA image, showing the inner portion of the jet. The prominent spiral galaxy in the upper right of the large-scale image is not related to 0313-192, nearly a billion light-years from Earth, but is more than 200 million light-years closer. The complex vertical structure of the absorbing dust and the blue star-forming regions past a warp in the dust lane confirm the spiral nature of the galaxy, even though it is seen edge-on.

Credit: NASA, W. Keel (University of Alabama), M. Ledlow (Gemini Observatory), F. Owen (NRAO) and AUI/NSF

A Tiny Galaxy is Born

The distorted shape of this tiny object, called POX 186, is evidence that it is a dwarf galaxy in the process of formation. This image, obtained by NASA's Hubble Space Telescope, shows the bluish-white glow of newborn stars at the galaxy's core, and an arch of stars (at right). Both features suggest a recent collision between two smaller clumps of stars that occurred within the past 100 million years. Gravity will eventually pull these stars together into a more symmetrical form. The red objects at the edges of the images are most likely more distant galaxies.

The Hubble images reveal POX 186 to be extremely small by galaxy standards, measuring only about 900 light-years across and containing just 10 million stars. By contrast, the Milky Way galaxy is about 100,000 light-years across and contains over 100 billion stars.

The galaxy is 68 million light-years away in the constellation Virgo. This color image was created from a composite of three pictures obtained by the Wide Field and Planetary Camera 2 in March and June 2000, and approximates what the galaxy would look like to the human eye.

Credit: NASA and Michael Corbin (CSC/STScI)

Irregular Galaxy NGC6240 as imaged by HST & Chandra

The Supermassive Black Holes of NGC 6240

The Hubble optical image on the left shows NGC 6240 in the throes of a titanic galaxy - galaxy collision 400 million light-years away. As the cosmic catastrophe plays out, the merging galaxies spew forth distorted tidal tails of stars, gas, and dust and undergo frantic bursts of star formation. Using the orbiting Chandra Observatory's x-ray vision to peer within the bright central regions of NGC 6242 astronomers believe they have uncovered, for the first time, not one but two enormous orbiting black holes, by detecting the characteristic x-ray radiation from the interstellar debris swirling toward them. In the false-color close-up view at right, the x-ray data clearly show the black hole sources (shaded blue) separated by about 3,000 light-years. Einstein's theory of gravity predicts that such a pair of black holes must spiral closer together, and ultimately coalesce into a single, even more massive black hole after several hundred million years. In the final moments the merging supermassive black holes will produce an extremely powerful burst of gravitational radiation.

Credit: Optical: R.P.van der Marel & J.Gerssen (STScI), NASA;
X-ray: S.Komossa & G.Hasinger (MPE) et al., CXC, NASA

The center of M87 as imaged by the HST and the VLBA

VLBA Reveals Formation Region of Giant Cosmic Jet Near a Black Hole

Space Telescope Science Institute astronomers and their co-investigators have gained their first glimpse of the mysterious region near a black hole at the heart of a distant galaxy, where a powerful stream of subatomic particles spewing outward at nearly the speed of light is formed into a beam, or jet, that then goes nearly straight for thousands of light-years. The astronomers used radio telescopes in Europe and the U.S., including the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) to make the most detailed images ever of the center of the galaxy M87, some 50 million light-years away.
The VLA and VLBA are instruments of the National Radio Astronomy Observatory, a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD.

Barred Spiral Galaxy NGC1512 as imaged by the HST

Hubble Unveils a Galaxy in Living Color

In this view of the center of the magnificent barred spiral galaxy NGC 1512, NASA Hubble Space Telescope’s broad spectral vision reveals the galaxy at all wavelengths from ultraviolet to infrared. The colors (which indicate differences in light intensity) map where newly born star clusters exist in both "dusty" and "clean" regions of the galaxy.
This color-composite image was created from seven images taken with three different Hubble cameras: the Faint Object Camera (FOC), the Wide Field and Planetary Camera 2 (WFPC2), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
NGC 1512 is a barred spiral galaxy in the southern constellation of Horologium. Located 30 million light-years away, relatively "nearby" as galaxies go, it is bright enough to be seen with amateur telescopes. The galaxy spans 70,000 light-years, nearly as much as our own Milky Way galaxy.
The galaxy’s core is unique for its stunning 2,400 light-year-wide circle of infant star clusters, called a "circumnuclear" starburst ring. Starbursts are episodes of vigorous formation of new stars and are found in a variety of galaxy environments.
Taking advantage of Hubble’s sharp vision, as well as its unique wavelength coverage, a team of Israeli and American astronomers performed one of the broadest and most detailed studies ever of such star-forming regions. The results, which will be published in the June issue of the Astronomical Journal, show that in NGC 1512 newly born star clusters exist in both dusty and clean environments. The clean clusters are readily seen in ultraviolet and visible light, appearing as bright, blue clumps in the image. However, the dusty clusters are revealed only by the glow of the gas clouds in which they are hidden, as detected in red and infrared wavelengths by the Hubble cameras. This glow can be seen as red light permeating the dark, dusty lanes in the ring.
"The dust obscuration of clusters appears to be an on-off phenomenon," says Dan Maoz, who headed the collaboration. "The clusters are either completely hidden, enshrouded in their birth clouds, or almost completely exposed." The scientists believe that stellar winds and powerful radiation from the bright, newly born stars have cleared away the original natal dust cloud in a fast and efficient "cleansing" process.
Aaron Barth, a co-investigator on the team, adds: "It is remarkable how similar the properties of this starburst are to those of other nearby starbursts that have been studied in detail with Hubble." This similarity gives the astronomers the hope that, by understanding the processes occurring in nearby galaxies, they can better interpret observations of very distant and faint starburst galaxies. Such distant galaxies formed the first generations of stars, when the universe was a fraction of its current age.
Circumstellar star-forming rings are common in the universe. Such rings within barred spiral galaxies may in fact comprise the most numerous class of nearby starburst regions. Astronomers generally believe that the giant bar funnels the gas to the inner ring, where stars are formed within numerous star clusters. Studies like this one emphasize the need to observe at many different wavelengths to get the full picture of the processes taking place.
Credit: NASA, ESA, and D. Maoz (Tel-Aviv University and Columbia University)

Members of the group of scientists involved in these observations are: Dan Maoz (Tel-Aviv University, Israel and Columbia University, USA), Aaron J. Barth (Harvard-Smithsonian Center for Astrophysics, USA), Luis C. Ho (The Observatories of the Carnegie Institution of Washington, USA), Amiel Sternberg (Tel-Aviv University, Israel) and Alexei V. Filippenko (University of California, Berkeley, USA).

Spiral Galaxy NGC 2787 as imaged by the HST

A Galaxy That's All Wound Up

Tightly wound, almost concentric, arms of dark dust encircle the bright nucleus of galaxy NGC 2787 in this NASA Hubble Space Telescope image created by the Hubble Heritage Team.
In astronomer Edwin Hubble's galaxy classification scheme, NGC 2787 is classified as an SB0, a barred lenticular galaxy. These lens-shaped galaxies show little or no evidence of the grand spiral arms that occur in their more photogenic cousins, though NGC 2787 does sport a faint bar, not apparent in this image.
NGC 2787's seemingly bland qualities are, however, just what the doctor ordered for astronomer Marcella Carollo's investigation. Dr. Carollo (Swiss Federal Institute of Technology, Zurich) and team used Hubble to look at the center of these galaxies for clues about the process of galaxy formation including the role of galaxy collisions and central black holes.
Also visible in the Heritage image are about a dozen globular clusters hovering around NGC 2787. What appear to be stars are, in fact, gravitationally bound families of 100,000's of ancient stars orbiting the center of NGC 2787.
NGC 2787 lies roughly 24 million light-years (7.4 megaparsecs) from Earth in the constellation Ursa Major. Data was collected with the Wide Field Planetary Camera 2 in January 1999. This Heritage image was made by combining light from blue, green and infrared filters from the 1999 dataset.
Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: M. Carollo (Swiss Federal Institute of Technology, Zurich)

Spiral Galaxy NGC 4319 and Quasar Markarian 205

Odd Couple Widely Separated by Time and Space

Appearances can be deceiving. In this NASA Hubble Space Telescope image, an odd celestial duo, the spiral galaxy NGC 4319 [center] and a quasar called Markarian 205 [upper right], appear to be neighbors. In reality, the two objects don't even live in the same city. They are separated by time and space.
NGC 4319 is 80 million light-years from Earth. Markarian 205 (Mrk 205) is more than 14 times farther away, residing 1 billion light-years from Earth. The apparent close alignment of Mrk 205 and NGC 4319 is simply a matter of chance. Astronomers used two methods to determine the distances to these objects. First, they measured how their light has been stretched in space due to the universe's expansion. Then they measured how much the ultraviolet light from Mrk 205 dimmed as it passed through the interstellar gas of NGC 4319.
The Hubble Wide Field and Planetary Camera 2 image shows the inner region of NGC 4319. In addition to the galaxy's inner spiral arms, an outer arm is faintly visible at lower left. The unusually dark and misshapen dust lanes in the galaxy's inner region are evidence of a disturbance, probably caused by an earlier interaction with another galaxy, NGC 4291, which is not in the photograph.
At a distance of 1 billion light-years, Mrk 205 is a relatively nearby quasar. Many quasars reside much farther away. Quasars, once known only as mysterious point-like objects, are now known to be distant galaxies that have extremely bright cores. These powerhouses of light are probably fueled by massive black holes. With powerful telescopes like Hubble, it is often possible to see the quasar's surrounding halo of faint starlight, as is clearly visible around Mrk 205.
Mrk 205 has a companion, a compact galaxy just below it. The objects appear to be interacting. The compact galaxy may be responsible for the structure in Mrk 205's halo.
The Hubble image shows that interacting galaxies and disturbances within galaxies are a rich source of information about galaxy structure and evolution.
Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: R. Knacke (Penn State Erie)

Behind a Dusty Veil Lies a Cradle of Star Birth

NGC 253 is a large, almost edge-on spiral galaxy, and is one of the nearest galaxies beyond our local neighborhood of galaxies. This dramatic galaxy shows complex structures such as clumpy gas clouds, darkened dust lanes, and young, luminous central star clusters. These elements are typical of spiral galaxies. Caroline Herschel discovered NGC 253 in 1783 while looking for comets. The galaxy's closeness to Earth makes it an ideal target for amateur astronomers who can see the southern sky and for astronomers interested in learning more about the makeup of these stunning cities of stars.

Credit: Hubble Heritage Team (AURA/STScI/NASA)

A Wheel within a Wheel

A nearly perfect ring of hot, blue stars pinwheels about the yellow nucleus of an unusual galaxy known as Hoag's Object. This image from NASA's Hubble Space Telescope captures a face-on view of the galaxy's ring of stars, revealing more detail than any existing photo of this object. The image may help astronomers unravel clues on how such strange objects form.
The entire galaxy is about 120,000 light-years wide, which is slightly larger than our Milky Way Galaxy. The blue ring, which is dominated by clusters of young, massive stars, contrasts sharply with the yellow nucleus of mostly older stars. What appears to be a "gap" separating the two stellar populations may actually contain some star clusters that are almost too faint to see. Curiously, an object that bears an uncanny resemblance to Hoag's Object can be seen in the gap at the one o'clock position. The object is probably a background ring galaxy.
Ring-shaped galaxies can form in several different ways. One possible scenario is through a collision with another galaxy. Sometimes the second galaxy speeds through the first, leaving a "splash" of star formation. But in Hoag's Object there is no sign of the second galaxy, which leads to the suspicion that the blue ring of stars may be the shredded remains of a galaxy that passed nearby. Some astronomers estimate that the encounter occurred about 2 to 3 billion years ago.
This unusual galaxy was discovered in 1950 by astronomer Art Hoag. Hoag thought the smoke-ring-like object resembled a planetary nebula, the glowing remains of a Sun-like star. But he quickly discounted that possibility, suggesting that the mysterious object was most likely a galaxy. Observations in the 1970s confirmed this prediction, though many of the details of Hoag's galaxy remain a mystery.
The galaxy is 600 million light-years away in the constellation Serpens. The Wide Field and Planetary Camera 2 took this image on July 9, 2001.
Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: Ray A. Lucas (STScI/AURA)

NICMOS Finds a Golden Ring at the Heart of a Galaxy

The revived Near Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard NASA's Hubble Space Telescope has pierced the dusty disk of the edge-on galaxy NGC 4013 and peered all the way to the galactic core. To the surprise of astronomers, NICMOS found a brilliant band-like structure, that may be a ring of newly formed stars [yellow band in middle photo] seen edge-on.
In the visible-light view of the galaxy [top photo], the star-forming ring cannot be seen because it is embedded in dust. The most prominent feature in the visible-light image — taken by the Wide Field and Planetary Camera 2 (WFPC2) — is the thin, dark band of gas and dust, which is about 500 light-years thick.
NICMOS enables the Hubble telescope to see in near-infrared wavelengths of light, so that it can penetrate the dust that obscures the inner hub of the galaxy. The ring-like structure spied by NICMOS encircles the core and is about 720 light-years wide, which is the typical size of most star-forming rings found in disk galaxies.
The small ring is churning out stars at a torrid pace. The Milky Way Galaxy, for example, is more than 10,000 times larger than the ring. If the Milky Way produced stars at the same rate, it would be making 1,000 times more stars a year.
The human eye cannot see infrared light, so colors have been assigned to correspond with near-infrared wavelengths. The blue light represents shorter near-infrared wavelengths and the red light corresponds to longer wavelengths.
The ring-like structure is seen more clearly in the photo at bottom. This picture, taken with a filter sensitive to hydrogen, shows the glow of stars and gas. Astronomers used this information to calculate the rate of star formation in the ring-like structure.
The extremely bright star near the center of each picture is a nearby foreground star belonging to our own Milky Way.
Rings of developing stars are common in barred spiral galaxies, which have "bars" of stars and gas slicing across their disks. The bars funnel gas to the galactic cores. But gravitational disturbances near the cores cause gas to accumulate into a lane or a ring. The gas then condenses to form stars. Because NGC 4013 is seen edge-on, astronomers don't know whether a bar of gas or some other mechanism formed the ring-like structure.
NGC 4013, which looks similar to our Milky Way Galaxy, resides in the constellation Ursa Major, 55 million light-years from Earth.
The middle picture is a color composite image that was made by combining photographs taken with the J-band, H-band, and Paschen-alpha filters. The bottom picture was taken with the Paschen-alpha filter. The images were taken on May 12.

Credits for NICMOS images: NASA, the NICMOS Group (STScI, ESA), and the NICMOS Science Team (University of Arizona)
Credits for WFPC2 image: NASA, the Hubble Heritage Team (STScI/AURA) and ESA

Faraway Galaxies Provide a Stunning "Wallpaper" Backdrop for a Runaway Galaxy

Against a stunning backdrop of thousands of galaxies, this odd-looking galaxy with the long streamer of stars appears to be racing through space, like a runaway pinwheel firework.
This picture of the galaxy UGC 10214 was taken by the Advanced Camera for Surveys (ACS), which was installed aboard NASA's Hubble Space Telescope in March during Servicing Mission 3B. Dubbed the "Tadpole," this spiral galaxy is unlike the textbook images of stately galaxies. Its distorted shape was caused by a small interloper, a very blue, compact galaxy visible in the upper left corner of the more massive Tadpole. The Tadpole resides about 420 million light-years away in the constellation Draco.

Seen shining through the Tadpole's disk, the tiny intruder is likely a hit-and-run galaxy that is now leaving the scene of the accident. Strong gravitational forces from the interaction created the long tail of debris, consisting of stars and gas that stretch out more than 280,000 light-years.
Numerous young blue stars and star clusters, spawned by the galaxy collision, are seen in the spiral arms, as well as in the long "tidal" tail of stars. Each of these clusters represents the formation of up to about a million stars. Their color is blue because they contain very massive stars, which are 10 times hotter and 1 million times brighter than our Sun. Once formed, the star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. These clusters will eventually become old globular clusters similar to those found in essentially all halos of galaxies, including our own Milky Way.
Two prominent clumps of young bright blue stars in the long tail are separated by a "gap" — a section that is fainter than the rest of the tail. These clumps of stars will likely become dwarf galaxies that orbit in the Tadpole's halo.
The galactic carnage and torrent of star birth are playing out against a spectacular backdrop: a "wallpaper pattern" of 6,000 galaxies. These galaxies represent twice the number of those discovered in the legendary Hubble Deep Field, the orbiting observatory's "deepest" view of the heavens, taken in 1995 by the Wide Field and Planetary Camera 2. The ACS picture, however, was taken in one-twelfth the time it took to observe the original Hubble Deep Field. In blue light, ACS sees even fainter objects than were seen in the "deep field." The galaxies in the ACS picture, like those in the deep field, stretch back to nearly the beginning of time. They are a myriad of shapes and represent fossil samples of the universe's 13-billion-year evolution.
The ACS image is so sharp that astronomers can identify distant colliding galaxies, the "building blocks" of galaxies, an exquisite "Whitman's Sampler" of galaxies, and many extremely faraway galaxies.
ACS made this observation on April 1 and 9, 2002. The color image is constructed from three separate images taken in near-infrared, orange, and blue filters.
Credit: NASA and the ACS Science Team

Burst of Star Formation Drives Bubble in Galaxy’s Core

These NASA Hubble Space Telescope snapshots reveal dramatic activities within the core of the galaxy NGC 3079, where a lumpy bubble of hot gas is rising from a cauldron of glowing matter.
The picture at left shows the bubble in the center of the galaxy's disk. The structure is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disk. The smaller photo at right is a close-up view of the bubble. Astronomers suspect that the bubble is being blown by "winds" (high-speed streams of particles) released during a burst of star formation. Gaseous filaments at the top of the bubble are whirling around in a vortex and are being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. The two white dots just above the bubble are probably stars in the galaxy.
The close-up reveals that the bubble's surface is lumpy, consisting of four columns of gaseous filaments that tower above the galaxy's disk. The filaments disperse at a height of 2,000 light-years. Each filament is about 75 light-years wide. Velocity measurements taken by the Canada-France-Hawaii Telescope in Hawaii show that the gaseous filaments are ascending at more than 4 million miles an hour (6 million kilometers an hour).
According to theoretical models, the bubble formed when ongoing winds from hot stars mixed with small bubbles of very hot gas from supernova explosions. Observations of the core's structure by radio telescopes indicate that those processes are still active. The models suggest that this outflow began about a million years ago. They occur about every 10 million years. Eventually, the hot stars will die, and the bubble's energy source will fade away. Astronomers have seen evidence of previous outbursts from radio and X-ray observations. Those studies show rings of dust and gas and long plumes of material, all of which are larger than the bubble.
NGC 3079 is 50 million light-years from Earth in the constellation Ursa Major. The colors in this image accentuate important details in the bubble. Glowing gas is red and starlight is blue/green. Hubble's Wide Field and Planetary Camera 2 snapped this picture in 1998. The results appear in the July 1, 2001 issue of the Astrophysical Journal.
Credits: NASA, Gerald Cecil (University of North Carolina), Sylvain Veilleux (University of Maryland), Joss Bland-Hawthorn (Anglo- Australian Observatory), and Alex Filippenko (University of California at Berkeley).

NGC 4622 Spiral Galaxy

Astronomers have found a spiral galaxy that may be spinning to the beat of a different cosmic drummer.

To the surprise of astronomers, the galaxy, called NGC 4622, appears to be rotating in the opposite direction to what they expected. Pictures by NASA's Hubble Space Telescope helped astronomers determine that the galaxy may be spinning clockwise by showing which side of the galaxy is closer to Earth. A Hubble telescope photo of the oddball galaxy is this month's Hubble Heritage offering. The image shows NGC 4622 and its outer pair of winding arms full of new stars [shown in blue].
Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two "leading" outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a "trailing" inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise.
NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. What caused this galaxy to behave differently from most galaxies? Astronomers suspect that NGC 4622 interacted with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a small companion galaxy. The galaxy's core provides new evidence for a merger between NGC 4622 and a smaller galaxy. This information could be the key to understanding the unusual leading arms.
Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way Galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 resides 111 million light-years away in the constellation Centaurus. The pictures were taken in May 2001 with Hubble's Wide Field Planetary Camera 2.
The science team, consisting of Ron Buta and Gene Byrd from the University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State Community College in Alabama, observed NGC 4622 in ultraviolet, infrared, and blue and green filters. Their composite image and science findings were presented at the meeting of the American Astronomical Society in January of 2002.
Image Credit: NASA and the Hubble Heritage Team (STScI/AURA) Acknowledgment: Dr. Ron Buta (U. Alabama), Dr. Gene Byrd (U. Alabama) and Tarsh Freeman (Bevill State Community College)

Hubble Reveals Ultraviolet Galactic Ring

The appearance of a galaxy can depend strongly on the color of the light with which it is viewed. The Hubble Heritage image of NGC6782 illustrates a pronounced example of this effect. This spiral galaxy, when seen in visible light, exhibits tightly wound spiral arms that give it a pinwheel shape similar to that of many other spirals. However, when the galaxy is viewed in ultraviolet light with NASA's Hubble Space Telescope, its shape is startlingly different. Ultraviolet light has a shorter wavelength than ordinary visible light, and is emitted from stars that are much hotter than the Sun. At ultraviolet wavelengths, which are rendered as blue in the Hubble image, A beautiful HST image of Barred Spiral Galaxy NGC6782 NGC6782 shows a spectacular, nearly circular bright ring surrounding its nucleus. The ring marks the presence of many recently formed hot stars. Two faint, dusty spiral arms emerge from the outer edge of the blue ring and are seen silhouetted against the golden light of older and fainter stars. A scattering of blue stars at the outer edge of NGC6782 in the shape of two dim spiral arms shows that some star formation is occurring there too. The inner ring surrounds a small central bulge and a bar of stars, dust, and gas. This ring is itself part of a larger dim bar that ends in these two outer spiral arms. Astronomers are trying to understand the relationship between the star formation seen in the ultraviolet light and how the bars may help localize the star formation into a ring. NGC6782 is a relatively nearby galaxy, residing about 183 million light-years from Earth. The light from galaxies at much larger distances is stretched to longer, redder wavelengths ["redshifted"], due to the expansion of the universe. This means that if astronomers want to compare visible-light images of very distant galaxies with galaxies in our own neighborhood, they should use ultraviolet images of the nearby ones. Astronomers find that the distant galaxies tend to have different structures than nearby ones, even when they use the correct procedure of comparing visible light in distant galaxies with ultraviolet light from nearby ones. Since the distant galaxies are seen as they were billions of years ago, such observations are evidence that galaxies evolve with time. The Hubble image of NGC6782 was taken with the Wide Field Planetary Camera 2 (WFPC2) in June 2000 as part of an ultraviolet survey of 37 nearby galaxies. The observations were carried out by an international "Hubble mid-UV team" led by Dr. Rogier Windhorst of Arizona State University. Additional observations of NGC 6782 were made by the Hubble Heritage Team in June 2001. The color image was produced by combining data from both observing programs that were taken through color filters in the WFPC2 camera that isolated ultraviolet, blue, visible, and infrared light.

A Galaxy Blazes with Star Formation

According to the Hubble Heritage team, NASA's Hubble Space Telescope snapped this remarkable view of spiral galaxy NGC 3310, a rare class of galaxies known as "starburst" galaxies. It seems that most "typical" galaxies form new stars at a fairly slow rate, but members of a "starburst" galaxy blaze with extremely active star formation. Scientists using NASA's Hubble Space Telescope are perfecting a technique to determine the history of starburst activity in galaxies by using the colors of star clusters. Measuring the clusters' colors yields information about stellar temperatures. Since young stars are blue, and older stars redder, the colors can be related to the ages, somewhat similar to counting the rings in a fallen tree trunk in order to determine the tree's age.
An amazing image of Spiral Galaxy NGC3310 by HST

An amazing image of Spiral Galaxy NGC3310 by HST

The galaxy NGC 3310(mag10.9) is forming clusters of new stars at a prodigious rate. Astronomer Gerhardt Meurer of The Johns Hopkins University leads a team of collaborators who are studying several starburst galaxies, including NGC 3310, which is showcased in this weeks Hubble Vision image.
There are several hundred star clusters in NGC 3310, visible in the Heritage image as the bright blue diffuse objects that trace the galaxy's spiral arms. Each of these star clusters represents the formation of up to about a million stars, a process that takes less than 100,000 years. In addition, hundreds of individual young, luminous stars can be seen throughout the galaxy.
Once formed, the star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. Measurements in this image of the wide range of cluster colors show that they have ages ranging from about one million up to more than one hundred million years. This suggests that the starburst "turned on" over 100 million years ago. It may have been triggered when a companion galaxy collided with NGC 3310.
These observations may change astronomers' view of starbursts. Starbursts were once thought to be brief episodes, resulting from catastrophic events like a galactic collision. However, the wide range of cluster ages in NGC 3310 suggests that the starburst activity can continue for an extended interval, once triggered.
Located in the direction of the constellation Ursa Major, NGC 3310 has a distance of about 59 million light-years. Hubble's Wide Field Planetary Camera 2 was used to make observations of NGC 3310 in March 1997 and again in September 2000. The color rendition of the combined images was created by the Hubble Heritage Team.

NGC 4013: A Galaxy on the Edge

According to the Hubble Heritage team, NASA's Hubble Space Telescope snapped this remarkable view of a perfectly "edge-on" galaxy, NGC 4013. This new Hubble picture reveals with exquisite detail huge clouds of dust and gas extending along, as well as far above, the galaxy's main disk.

An amazing image of edge-on galaxy NGC4013 by HST

An amazing image of edge-on galaxy NGC4013 by HST

NGC 4013 is a spiral galaxy, similar to our own Milky Way, lying some 55 million light-years from Earth in the direction of the constellation Ursa Major. Viewed pole-on, it would look like a nearly circular pinwheel, but NGC 4013 happens to be seen edge-on from our vantage point. Even at 55 million light-years, the galaxy is larger than Hubble's field of view, and the image shows only a little more than half of the object, albeit with unprecedented detail.

Dark clouds of interstellar dust stand out in the picture because they absorb the light of background stars. Most of the clouds lie in the plane of the galaxy, forming the dark band, about 500 light-years thick, that appears to cut the galaxy in two from upper right to lower left. A similar effect can be seen in our own sky. If one views the Milky Way by going well away from city lights, dust clouds in the disk of our own galaxy appear to split the glowing band of the Milky Way in two.

New images from NASA's Hubble Space Telescope are helping researchers view in unprecedented detail the spiral arms and dust clouds of a nearby galaxy, which are the birth sites of massive and luminous stars.

An amazing image of M51 by the Hubble Space Telescope The Whirlpool galaxy, M51, has been one of the most photogenic galaxies in amateur and professional astronomy. Easily photographed and viewed by smaller telescopes, this celestial beauty is studied extensively in a range of wavelengths by large ground- and space-based observatories. This Hubble composite image shows visible starlight as well as light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms.

NASA's Hubble Space Telescope has captured this image of an unusual edge-on galaxy, revealing remarkable details of its warped dusty disk and showing how colliding galaxies spawn the formation of new generations of stars.

The dust and spiral arms of normal spiral galaxies, like our own Milky Way, appear flat when viewed edge-on. This Hubble Heritage image of ESO 510-G13 shows a galaxy that, by contrast, has an unusual twisted disk structure. ESO 510-G13 lies in the southern constellation Hydra, roughly 150 million light-years from Earth.

FIREWORKS OF STAR FORMATION LIGHT UP A GALAXY

Newly released images obtained with NASA'S Hubble Space Telescope in July 1997 reveal episodes of star formation that are occurring across the face of the nearby galaxy NGC 4214.

Located some 13 million light-years from Earth, NGC 4214 is currently forming clusters of new stars from its interstellar gas and dust. In the Hubble image, we can see a sequence of steps in the formation and evolution of stars and star clusters. The picture was created from exposures taken in several color filters with Hubble's Wide Field Planetary Camera 2.
NGC 4214 contains a multitude of faint stars covering most of the frame, but the picture is dominated by filigreed clouds of glowing gas surrounding bright stellar clusters.
The youngest of these star clusters are located at the lower right of the picture, where they appear as about half a dozen bright clumps of glowing gas. Each cloud fluoresces because of the strong ultraviolet light emitted from the embedded young stars, which have formed within them due to gravitational collapse of the gas.
Young, hot stars have a whitish to bluish color in the Hubble image, because of their high surface temperatures, ranging from 10,000 up to about 50,000 degrees Celsius. In addition to pouring out ultraviolet light, these hot stars eject fast "stellar winds," moving at thousands of kilometers per second, which plow out into the surrounding gas. The radiation and wind forces from the young stars literally blow bubbles in the gas. Over millions of years, the bubbles increase in size as the stars inside them grow older.
Moving to the lower left from the youngest clusters, we find an older star cluster, around which a gas bubble has inflated to the point that there is an obvious cavity around the central cluster.
The most spectacular feature in the Hubble picture lies near the center of NGC 4214. This object is a cluster of hundreds of massive blue stars, each of them more than 10,000 times brighter than our own Sun. A vast heart-shaped bubble, inflated by the combined stellar winds and radiation pressure, surrounds the cluster. The expansion of the bubble is augmented as the most massive stars in the center reach the ends of their lives and explode as supernovae.
Deprived of gas, the cluster at the center of NGC 4214 will be unable to form further new stars, and its luminous stars will continue to go supernova and disappear. Elsewhere in the galaxy, however, gas will start to collapse and form yet another new generation of stars, even as the clusters visible today gradually fade away.
The faint stars covering most of the picture are much older than the bright blue supergiants, and show us that episodes of star birth have been occurring in NGC 4214 for billions of years.
The principal astronomers are: John MacKenty, Jesús Maíz-Apellániz (Space Telescope Science Institute), Colin Norman (Johns Hopkins University), Nolan Walborn (Space Telescope Science Institute), Richard Burg (Johns Hopkins University), Richard Griffiths (Carnegie Mellon University), and Rosemary Wyse (Johns Hopkins University).
Image Credit: NASA and The Hubble Heritage Team (STScI)
Acknowledgment: J. MacKenty and J. Maíz-Apellániz (STScI)

A Cosmic Searchlight

Streaming out from the center of the galaxy M87

like a cosmic searchlight is one of nature's most amazing phenomena, a black-hole powered jet of electrons and other sub-atomic particles traveling at nearly the speed of light. In this NASA Hubble Space Telescope image, the blue of the jet contrasts with the yellow glow from the combined light of billions of unseen stars and the yellow, point-like globular clusters that make up this galaxy.
At first glance, M87 (also known as NGC 4486) appears to be an ordinary giant elliptical galaxy; one of many ellipticals in the nearby Virgo cluster of galaxies. However, as early as 1918, astronomer H.D. Curtis noted a "curious straight ray" protruding from M87. In the 1950s when the field of radio was blossoming, one of the brightest radio sources in the sky, Virgo A, was discovered to be associated with M87 and its jet.
After decades of study, prompted by these discoveries, the source of this incredible amount of energy powering the jet has become clear. Lying at the center of M87 is a supermassive black hole, which has swallowed up a mass equivalent to 2 billion times the mass of our Sun. The jet originates in the disk of superheated gas swirling around this black hole and is propelled and concentrated by the intense, twisted magnetic fields trapped within this plasma. The light that we see (and the radio emission) is produced by electrons twisting along magnetic field lines in the jet, a process known as synchrotron radiation, which gives the jet its bluish tint.
M87 is one of the nearest and is the most well-studied extragalactic jet, but many others exist. Wherever a massive black hole is feeding on a particularly rich diet of disrupted stars, gas, and dust, the conditions are right for the formation of a jet. Interestingly, a similar phenomenon occurs around young stars, though at much smaller scales and energies.
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead,themselves clusters of hundreds of thousands of stars each. An estimated 15,000 globular clusters formed very early in the history of this galaxy and are older than the second generation of stars, which huddle closer to the center of the galaxy.
The data were collected with Hubble's Wide Field Planetary Camera 2 in 1998 by J.A. Biretta, W.B. Sparks, F.D. Macchetto, and E.S. Perlman (STScI). The Hubble Heritage team combined these exposures of ultraviolet, blue, green, and infrared light in order to create this color image.
Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: J.A. Biretta, W.B. Sparks, F.D. Macchetto, E.S. Perlman (STScI)

Biggest 'Zoom Lens' Takes Hubble Deeper into the Universe

A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA's Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. The gravity of the cluster's trillion stars — plus dark matter — acts as a 2-million-light-year-wide "lens" in space. This "gravitational lens" bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6).

Though gravitational lensing has been studied previously by Hubble and ground-based telescopes, this phenomenon has never been seen before in such detail. The ACS picture reveals 10 times more arcs than would be seen by a ground-based telescope. The ACS is 5 times more sensitive and provides pictures that are twice as sharp as the previous work-horse Hubble cameras. So it can see the very faintest arcs with greater clarity. The picture presents an immense jigsaw puzzle for Hubble astronomers to spend months untangling. Interspersed with the foreground cluster are thousands of galaxies, which are lensed images of the galaxies in the background universe. Detailed analysis of the images promises to shed light on galaxy evolution, the curvature of space, and the mystery of dark matter. The picture is an exquisite demonstration of Albert Einstein's prediction that gravity warps space and distorts beams of light.

This representative color image is a composite of visible-light and near-infrared exposures taken in June 2002.

Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA

Multi-Galactic destruction as imaged by HST

Hubble Watches Galaxies Engage in Dance of Destruction

NASA's Hubble Space Telescope is witnessing a grouping of galaxies engaging in a slow dance of destruction that will last for billions of years. The galaxies are so tightly packed together that gravitational forces are beginning to rip stars from them and distort their shapes. Those same gravitational forces eventually could bring the galaxies together to form one large galaxy. The name of this grouping, Seyfert's Sextet, implies that six galaxies are participating in the action. But only four galaxies are on the dance card. The small face-on spiral with the prominent arms [center] of gas and stars is a background galaxy almost five times farther away than the other four. Only a chance alignment makes it appear as if it is part of the group. The sixth member of the sextet isn't a galaxy at all but a long "tidal tail" of stars [below, right] torn from one of the galaxies. The group resides 190 million light-years away in the constellation Serpens.
This densely packed grouping spans just 100,000 light-years, occupying less volume than the Milky Way galaxy. Each galaxy is about 35,000 light-years wide. Three of the galaxies [the elliptical galaxy, second from top, and the two spiral galaxies at the bottom] bear the telltale marks of close interactions with each other, or perhaps with an interloper galaxy not pictured here. Their distorted shapes suggest that gravitational forces have reshaped them. The halos around the galaxies indicate that stars have been ripped away. The galaxy at bottom, center, has a 35,000 light-year-long tail of stars flowing from it. The tail may have been pulled from the galaxy about 500 million years ago.
Although part of the group, the nearly edge-on spiral galaxy at top, center, remains relatively undisturbed, except for the slight warp in its disk. Most of its stars have remained within its galactic boundaries.
Unlike most other galaxy interactions observed with the Hubble telescope, this group shows no evidence of the characteristic blue regions of young star clusters, which generally arise during galaxy interactions.
The lack of star-forming clusters suggests that there is something different about Seyfert's Sextet compared with similar systems. One example is Stephan's Quintet, another congregation of interacting galaxies observed with the Hubble telescope. The difference between the two systems could be a simple one: astronomers may be seeing the sextet at the beginning of its interaction, before much has happened. This will not be the case for long, though. The galaxies in Seyfert's Sextet will continue to interact, and eventually, billions of years from now, all four may merge and form a single galaxy. Astronomers have strong evidence that many, if not most, elliptical galaxies are the result of mergers.
Astronomers named the grouping Seyfert's Sextet for astronomer Carl Seyfert, who discovered the assemblage in the late 1940s. Seyfert already suspected that one apparent member of the sextet was not a galaxy but simply a tidal tail stripped off of one of the other members.
The image was taken on June 26, 2000, with the Wide Field and Planetary Camera 2.
Image Credit: NASA, J. English (U. Manitoba), S. Hunsberger, S. Zonak, J. Charlton, S. Gallagher (PSU), and L. Frattare (STScI)
Science Credit: NASA, C. Palma, S. Zonak, S. Hunsberger, J. Charlton, S. Gallagher, P. Durrell (The Pennsylvania State University) and J. English (University of Manitoba)

Multiple Galaxy Collisions Surprise Hubble Astronomers

Hubble astronomers conducting research on a class of galaxies called ultra-luminous infrared galaxies (ULIRG) have discovered that over two dozen of these are found within "nests" of galaxies, apparently engaged in multiple collisions that lead to fiery pile-ups of three, four or even five galaxies smashing together.

Borne's co-investigators are Howard Bushouse (Space Telescope Science Institute), Luis Colina (Instituto de Fisica de Cantabria, Spain) and Ray Lucas (Space Telescope Science Institute).

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.

The Hubble Deep Field

Galaxies like colorful pieces of candy fill the Hubble Deep Field - one of humanity's most distant optical views of the Universe. The dimmest, some as faint as 30th magnitude (about four billion
times fainter than stars visible to the unaided eye), are very distant galaxies and represent what the Universe looked like in the extreme past, perhaps less than one billion years after the Big Bang. To make the
Deep Field image, astronomers selected an uncluttered area of the sky in the constellation Ursa Major (the Big Bear) and pointed the Hubble Space Telescope at a single spot for 10 days accumulating and
combining many separate exposures. With each additional exposure, fainter objects were revealed. The final result has been used to explore the mysteries of galaxy evolution and the infant Universe.

Gravitational Lens Helps Hubble and Keck Discover Galaxy Building Block

This NASA Hubble Space Telescope image

shows a very small, faint galaxy 'building block' newly discovered by a unique collaboration between ground- and space-based telescopes. Hubble and the 10-meter Keck Telescopes in Hawaii joined forces, using a galaxy cluster which acts as gravitational lens to detect what scientists believe is one of the smallest very distant objects ever found.
The galaxy cluster Abell 2218 was used by a team of European and American astronomers led by Richard Ellis (Caltech) in their systematic search for intrinsically faint distant star-forming systems. Without help from Abell 2218's exceptional magnifying power to make objects appear about 30 times brighter, the galaxy building block would have been undetectable.
In the image to the right, the object is seen distorted into two nearly identical, very red 'images' by the gravitational lens. The image pair represents the magnified result of a single background object gravitationally lensed by Abell 2218 and viewed at a distance of 13.4 billion light-years. The intriguing object contains only one million stars, far fewer than a mature galaxy, and scientists believe it is very young. Such young star-forming systems of low mass at early cosmic times are likely to be the objects from which present-day galaxies have formed.
In the image to the left, the full overview of the galaxy cluster Abell 2218 is seen. This image was taken by Hubble in 1999 at the completion of Hubble Servicing Mission 3A.
Credit: NASA, ESA, Richard Ellis (Caltech) and Jean-Paul Kneib (Observatoire Midi-Pyrenees, France
Acknowledgment: NASA, A. Fruchter and the ERO Team (STScI and ST-ECF)

This visible-light picture

, taken by NASA's Hubble Space Telescope, reveals an intergalactic "pipeline" of material flowing between two battered galaxies that bumped into each other about 100 million years ago. The pipeline [the dark string of matter] begins in NGC 1410 [the galaxy at left], crosses over 20,000 light-years of intergalactic space, and wraps around NGC 1409 [the companion galaxy at right] like a ribbon around a package. Although astronomers have taken many stunning pictures of galaxies slamming into each other, this image represents the clearest view of how some interacting galaxies dump material onto their companions. These results are being presented today at the 197th meeting of the American Astronomical Society in San Diego, CA.
Astronomers used the Space Telescope Imaging Spectrograph to confirm that the pipeline is a continuous string of material linking both galaxies.
Scientists believe that the tussle between these compact galaxies somehow created the pipeline, but they're not certain why NGC 1409 was the one to begin gravitationally siphoning material from its partner. And they don't know where the pipeline begins in NGC 1410. More perplexing to astronomers is that NGC 1409 is seemingly unaware that it is gobbling up a steady flow of material. A stream of matter funneling into the galaxy should have fueled a spate of star birth. But astronomers don't see it. They speculate that the gas flowing into NGC 1409 is too hot to gravitationally collapse and form stars.
Astronomers also believe that the pipeline itself may contribute to the star-forming draught. The pipeline, a pencil-thin, 500 light-year-wide string of material, is moving a mere 0.02 solar masses of matter a year.
Astronomers estimate that NGC 1409 has consumed only about a million solar masses of gas and dust, which is not enough material to spawn some of the star-forming regions seen in our Milky Way. The low amount means that there may not be enough material to ignite star birth in NGC 1409, either. The glancing blow between the galaxies was enough, however, to toss stars deep into space and ignite a rash of star birth in NGC 1410. The arms of NGC 1410, an active, gas-rich spiral galaxy classified as a Seyfert, are awash in blue, the signature color of star-forming regions. The bar of material bisecting the center of NGC 1409 also is a typical byproduct of galaxy collisions.
Astronomers expect more fireworks to come. The galaxies are doomed to continue their game of "bumper cars," hitting each other and moving apart several times until finally merging in another 200 million years. The galaxies' centers are only 23,000 light-years apart, which is slightly less than Earth's distance from the center of the Milky Way. They are bound together by gravity, orbiting each other at 670,000 miles an hour (1 million kilometers an hour). The galaxies reside about 300 million light-years from Earth in the constellation Taurus. The Hubble picture was taken Oct. 25, 1999.
Credits: NASA, William C. Keel (University of Alabama, Tuscaloosa)

Star Clusters Born in the Wreckage of Cosmic Collisions

This close-up view of Stephan's Quintet

, a group of five galaxies, reveals a string of bright star clusters that sparkles like a diamond necklace. The clusters, each harboring up to millions of stars, were born from the violent interactions between some members of the group. The rude encounters also have distorted the galaxies' shapes, creating elongated spiral arms and long, gaseous streamers.
The NASA Hubble Space Telescope photo showcases three regions of star birth: the long, sweeping tail and spiral arms of NGC 7319 [near center]; the gaseous debris of two galaxies, NGC 7318B and NGC 7318A [top right]; and the area north of those galaxies, dubbed the northern starburst region [top left].
The clusters' bluish color indicates that they're relatively young. Their ages span from about 2 million to more than 1 billion years old. The brilliant star clusters in NGC 7318B's spiral arm (about 30,000 light-years long) and the northern starburst region are between 2 million and more than 100 million years old. NGC 7318B instigated the starburst by barreling through the region. The bully galaxy is just below NGC 7318A at top right. Although NGC7318B appears dangerously close to NGC7318A, it's traveling too fast to merge with its close neighbor. The partial galaxy on the far right is NGC 7320, a foreground galaxy not physically bound to the other galaxies in the picture.
About 20 to 50 of the clusters in the northern starburst region reside far from the coziness of galaxies. The clusters were born about 150,000 light-years from the nearest galaxy.
A galaxy that is no longer part of the group triggered another collision that wreaked havoc. NGC7320C [not in the photo] plowed through the quintet several hundred million years ago, pulling out the 100,000 light-year-long tail of gaseous debris from NGC7319. The clusters in NGC7319's streaming tail are 10 million to 500 million years old and may have formed at the time of the violent collision. The faint bluish object at the tip of the tail is a young dwarf galaxy, which formed in the gaseous debris.
The quintet is in the constellation Pegasus, 270 million light-years from Earth. Spied by Edouard M. Stephan in 1877, Stephan's Quintet is the first compact group ever discovered. The mosaic picture was taken by Hubble's Wide Field and Planetary Camera 2 on Dec. 30, 1998 and June 17, 1999.

Image Credits: NASA, Jayanne English (University of Manitoba), Sally Hunsberger (Pennsylvania State University), Zolt Levay (Space Telescope

Science Institute), Sarah Gallagher (Pennsylvania State University), and Jane Charlton (Pennsylvania State University)

GALACTIC SILHOUETTES

This new image from NASA's Hubble Space Telescope and its Wide Field Planetary Camera 2 (WFPC2) shows the unique galaxy pair called NGC 3314.

Through an extraordinary chance alignment, a face-on spiral galaxy lies precisely in front of another larger spiral. This line-up provides us with the rare chance to visualize dark material within the front galaxy, seen only because it is silhouetted against the object behind it.
Dust lying in the spiral arms of the foreground galaxy stands out where it absorbs light from the more distant galaxy. This silhouetting shows us where the interstellar dust clouds are located, and how much light they absorb. The outer spiral arms of the front galaxy appear to change from bright to dark, as they are projected first against deep space, and then against the bright background of the other galaxy.
NGC 3314 lies about 140 million light-years from Earth, in the direction of the southern hemisphere constellation Hydra. The bright blue stars forming a pinwheel shape near the center of the front galaxy have formed recently from interstellar gas and dust.
In many galaxies, interstellar dust lies only in the same regions as recently formed blue stars. However, in the foreground galaxy, NGC 3314a, there are numerous additional dark dust lanes that are not associated with any bright young stars.
A small, red patch near the center of the image is the bright nucleus of the background galaxy, NGC 3314b. It is reddened for the same reason the setting sun looks red. When light passes through a volume containing small particles (molecules in the Earth's atmosphere or interstellar dust particles in galaxies), its color becomes redder.
The Hubble Heritage color image of NGC 3314 was constructed from archival images taken with WFPC2 in April 1999 by Drs. William Keel and Ray White III (University of Alabama) in blue and infrared light, combined with new images obtained by the Heritage team in March 2000 using blue, green and red filters.
Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgments: William Keel (U. Alabama)

A Bird's Eye View of a Galaxy Collision

What appears as a bird's head, leaning over to snatch up a tasty meal is a striking example of a galaxy collision in NGC 6745. Interacting Galaxy System NGC6745 as imaged by HST

Interacting Galaxy System NGC6745 as imaged by HST

A large spiral galaxy, with its nucleus still intact, peers at the smaller passing galaxy (nearly out of the field of view at lower right), while a bright blue beak and bright whitish-blue top feathers show the distinct path taken during the smaller galaxy's journey. These galaxies did not merely interact gravitationally as they passed one another, they actually collided.
When galaxies collide, the stars that normally comprise the major portion of the luminous mass of each of the two galaxies will almost never collide with each other but will pass rather freely between each other with little damage. This occurs because the physical size of individual stars is tiny compared to their typical separations, making the chance of physical encounter relatively small. In our own Milky Way galaxy, the space between our Sun and our nearest stellar neighbor, Proxima Centauri (part of the Alpha Centauri triple system), is a vast 4.3 light-years.
However, the situation is quite different for the interstellar media in the above two galaxies - material consisting largely of clouds of atomic and molecular gases and of tiny particles of matter and dust, strongly coupled to the gas. Wherever the interstellar clouds of the two galaxies collide, they do not freely move past each other without interruption but, rather, suffer a damaging collision. High relative velocities cause ram pressures at the surface of contact between the interacting interstellar clouds. This pressure, in turn, produces material densities sufficiently extreme as to trigger star formation through grav