Galaxy Evolution Explorer (Galex)

[Waspie_Dwarf]

NASA Galaxy Hunter: Huge Black Holes Stifle Star Formation

Supermassive black holes in some giant galaxies create such a hostile environment, they shut down the formation of new stars, according to NASA Galaxy Evolution Explorer findings published in the August 24 issue of Nature.

The orbiting observatory surveyed more than 800 nearby elliptical galaxies of various sizes. An intriguing pattern emerged: the more massive, or bigger, the galaxy, the less likely it was to have young stars. Because bigger galaxies are known to have bigger black holes, astronomers believe the black holes are responsible for the lack of youthful stars.


Image above: This artist's concept depicts a supermassive black hole at the center of a galaxy. The blue color here represents radiation pouring out from material very close to the black hole. The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. Image credit: NASA/JPL-Caltech
+ Full image and caption
+ Browse version of image

"Supermassive black holes in these giant galaxies create unfriendly places for stars to form," said Dr. Sukyoung K. Yi of Yonsei University in Seoul, Korea, who led the research team. "If you want to find lots of young stars, look to the smaller galaxies."

Previously, scientists had predicted that black holes might have dire consequences for star birth, but they didn't have the tools necessary to test the theory. The Galaxy Evolution Explorer, launched in 2003, is well-suited for this research. It is extremely sensitive to the ultraviolet radiation emitted by even low numbers of young stars.

Black holes are monstrous heaps of dense matter at the centers of galaxies. Over time, a black hole and its host galaxy will grow in size, but not always at the same rate.

Yi and his collaborators found evidence that the black holes in elliptical galaxies bulk up to a critical mass before putting a stop to star formation. In other words, once a black hole reaches a certain size relative to its host galaxy, its harsh effects become too great for new stars to form. According to this "feedback" theory, the growth of a black hole slows the development of not only stars but of its entire galaxy.

How does a black hole do this? There are two possibilities. First, jets being blasted out of black holes could blow potential star-making fuel, or gas, out of the galaxy center, where stars tend to arise.


Image above: The Galaxy Evolution Explorer observed the following trend: the biggest galaxies and black holes (shown in upper right corner) are more likely to have no observable star formation (red) than the smaller galaxies with smaller black holes. This is evidence that black holes can create environments unsuitable for stellar birth.
Image credit: NASA/JPL-Caltech/Yonsei University
+ Full image and caption
+ Browse version of image

The second theory relates to the fact that black holes drag surrounding gas onto them, which heats the gas. The gas becomes so hot that it can no longer clump together and collapse into stars.

Other authors of this research include: Drs. Kevin Schawinski, Sadegh Khochfar and Sugata Kaviraj of the University of Oxford, England; Dr. Young-Wook Lee of Yonsei University in Seoul, Korea; Drs. Alessandro Boselli, Jose Donas and Bruno Milliard of the Laboratory of Astrophysics of Marseille, France; Tim Conrow, Drs. Tom Barlow, Karl Forster, Peter G. Friedman, D. Chris Martin, Patrick Morrissey, Mark Seibert, Todd Small and Ted K. Wyder of the California Institute of Technology in Pasadena; Dr. Susan Neff of NASA's Goddard Space Flight Center, Greenbelt, Maryland; Dr. David Schiminovich of Columbia University, N.Y.; Drs. Tim Heckman, Alex Szalay and Luciana Bianchi of Johns Hopkins University, Baltimore, Md.; Dr, Barry Madore of the Observatories of the Carnegie Institute of Washington in Pasadena; and Dr. R. Michael Rich of the University of California, Los Angeles.

Additional information about Galaxy Evolution Explorer is online at http://www.galex.caltech.edu .

The California Institute of Technology in Pasadena, Calif., leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers from South Korea and France collaborated on this mission.

Media contacts: Whitney Clavin/Jane Platt 818-354-4673/354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

2006-101

Source: NASA - Exploring The Universe - Stars and Galaxies

[Waspie_Dwarf]

NASA Telescope Sees Black Hole Munch on a Star

A giant black hole has been caught red-handed dipping into a cosmic cookie jar of stars by NASA's Galaxy Evolution Explorer. This is the first time astronomers have seen the whole process of a black hole eating a star, from its first to nearly final bites.

"This type of event is very rare, so we are lucky to study the entire process from beginning to end," said Dr. Suvi Gezari of the California Institute of Technology, Pasadena, Calif. Gezari is lead author of a new paper appearing in the Dec. 10 issue of Astrophysical Journal Letters.


Image right: This artist's concept shows a supermassive black hole at
the center of a remote galaxy digesting the remnants of a star.
Image credit: NASA/JPL-Caltech
+ Full image and caption

For perhaps thousands of years, the black hole rested quietly deep inside an unnamed elliptical galaxy. But then a star ventured a little too close to the sleeping black hole and was torn to shreds by the force of its gravity. Part of the shredded star swirled around the black hole, then began to plunge into it, triggering a bright ultraviolet flare that the Galaxy Evolution Explorer was able to detect.

Today, the space-based telescope continues to periodically watch this ultraviolet light fade as the black hole finishes the remaining bits of its stellar meal. The observations will ultimately provide a better understanding of how black holes evolve with their host galaxies.

"This will help us greatly in weighing black holes in the universe, and in understanding how they feed and grow in their host galaxies as the universe evolves," said Dr. Christopher Martin of Caltech, a co-author of the paper and the principal investigator for the Galaxy Evolution Explorer.

In the early 1990s, three other resting, or dormant, black holes were suspected of having eaten stars when the joint German-American-British R?ntgen X-ray satellite picked up X-ray flares from their host galaxies. Astronomers had to wait until a decade later for NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton X-ray observatory to confirm those findings, showing that the black holes' X-rays had faded dramatically -- a sign that stars were swallowed.

Now, Gezari and her colleagues have, for the first time, watched a similar feeding frenzy unfold, as it happens, through the ultraviolet eyes of the Galaxy Evolution Explorer. They used the telescope's detectors to catch an ultraviolet flare from a distant galaxy, then watched the flare diminish over time, as the galaxy's central black hole consumed the star. Additional data from Chandra, the Canada France Hawaii Telescope in Hawaii and the Keck Telescope, also in Hawaii, helped the team chronicle the event in multiple wavelengths over two years.

Black holes are heaps of concentrated matter whose gravity is so strong that even light cannot escape. Supermassive black holes are believed to reside at the cores of every galaxy, though some are thought to be more active than others. Active black holes drag surrounding material into them, heating it up and causing it to glow. Dormant black holes, like the one in our Milky Way galaxy, hardly make a peep, so they are difficult to study.

That's why astronomers get excited when an unsuspecting star wanders too close to a dormant black hole, an event thought to happen about once every 10,000 years in a typical galaxy. A star will flatten and stretch apart when a nearby black hole's gravity overcomes its own self-gravity. The same phenomenon happens on Earth every day, as the moon's gravity tugs on our world, causing the oceans to rise and fall. Once a star has been disrupted, a portion of its gaseous body will then be pulled into the black hole and heated up to temperatures that emit X-rays and ultraviolet light.

"The star just couldn't hold itself together," said Gezari, adding, "Now that we know we can observe these events with ultraviolet light, we've got a new tool for finding more."

The newfound feeding black hole is thought to be tens of millions times as massive as our sun. Its host galaxy is located 4 billion light-years away in the Bootes constellation.

An artist's concept and additional information about the Galaxy Evolution Explorer is online at http://www.nasa.gov/galex/.

The California Institute of Technology in Pasadena, Calif., leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

Media contact: Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

2006-144

Source: NASA - Missions - Galex

[Hazzard]

Thanks for posting that WD. I wonder how many Sol sized stars it would take "to fill its belly"?

Edited December 5, 2006 by hazzard

[Picturesque Orion]

Thanks for posting that WD. I wonder how many Sol sized stars it would take "to fill its belly"?

Isn't its belly infinite in volume?

[frogfish]

That's amazing...Thanks for the info Waspie

[Waspie_Dwarf]

Isn't its belly infinite in volume?

No. Black holes aren't actually holes. They are just very dense objects.

[Picturesque Orion]

No. Black holes aren't actually holes. They are just very dense objects.

I understand. I've read somewhere that they are not actually hole shaped, that they are the shape of a sphere.

[frogfish]

Black holes just keep gathering mass (from what they suck in). The rest forms an accretion disk.

Some of the mass is however ejected in powerful jets called Quasars.

[Waspie_Dwarf]

NASA Mission Finds Link Between Big and Small Stellar Blasts

Proof that certain double star systems can erupt in full-blown explosions and then continue to flare up with smaller bursts has been spotted by the ultraviolet eyes of NASA's Galaxy Evolution Explorer.

The finding bolsters a 20-year-old theory that suggests such double-star, or binary systems, should eventually undergo both types of explosion, rather than just one or the other. It implies the systems probably cycle between two blast types, hiccupping every few weeks with small surges until the next giant outburst about 10,000 years later.


Image above: This composite image shows Z Camelopardalis, or Z Cam,
a double-star system featuring a collapsed, dead star, and a companion
star, as well as a ghostly shell around the system.
Image credit: NASA/JPL-Caltech
+ Related animation

"The new images are the strongest evidence yet in favor of the cyclic evolution of these binary stars," said Dr. Mike Shara of the American Museum of Natural History, New York, lead author of a new paper that details the finding in the March 8 issue of the journal Nature. "It's gratifying to see such strong evidence for this theory finally emerge after all this time."

The new discovery centers around Z Camelopardalis (Z Cam), a stellar system that astronomers have long known to be a cataclysmic binary - a system featuring a collapsed, dead star, or white dwarf, which behaves like a vampire sucking hydrogen-rich matter from a companion star. The stolen material forms a rotating disk of gas and dust around the white dwarf.

Astronomers divide cataclysmic binaries into two classes - dwarf novae, which erupt in smaller, "hiccup-like" blasts, and classical novae, which undergo huge explosions. Classical novae explosions are 10,000 to a million times brighter than those of dwarf novae, and they leave behind large shells of shocked gas.

About 530 light years from Earth, Z Cam was one of the first dwarf novae ever detected. For decades, observers have watched the system hiccup with regular outbursts. It brightens about 40-fold every 3 weeks or so, when an instability causes some of the material drawn by the stellar vampire to crash onto the white dwarf's surface.


Image above: This enhanced image from
the far-ultraviolet detector on NASA's
Galaxy Evolution Explorer shows a ghostly
shell of ionized gas around Z Camelopardalis,
a binary, or double-star system featuring a
collapsed, dead star known as a white dwarf,
and a companion star.
Image credit: NASA/JPL-Caltech

Theory holds that Z Cam and other recurring dwarf novae should eventually accumulate enough matter and pressure from their swirling disks of hydrogen to trigger gigantic hydrogen bombs - classical novae explosions. But no one had found definitive evidence that a binary had experienced both types of blasts until the Galaxy Evolution Explorer's observations of Z Cam, which began in 2003.

That's when Dr. Mark Seibert of the Carnegie Institution of Washington in Pasadena, Calif., serendipitously noticed a never-before-seen arc and linear features surrounding Z Cam in imaging data the Galaxy Evolution Explorer collected during its Survey of Nearby Galaxies. The features indicated the presence of a massive shell around Z Cam - evidence that the dwarf nova had in fact undergone a classical nova explosion a few thousand years ago.

Previous observations had failed to reveal the massive shell because it cannot be easily detected at optical wavelengths. It is, however, easily seen at the ultraviolet wavelengths detected by the Galaxy Evolution Explorer.

"You could actually see it immediately," Seibert said. "But we had to convince ourselves that we were really seeing a nova remnant."

Narrowband images from Kitt Peak National Observatory near Tucson, Ariz., Palomar Observatory near San Diego, Calif., and the Wise Observatory near Mizpe Ramon, Israel, along with optical spectroscopic measurements made at the Lick Observatory near San Jose, Calif., by other team members confirmed that the structures detected in the Galaxy Evolution Explorer imaging data were indeed a massive shell of gas surrounding Z Cam.

The authors of the new paper write that Z Cam's classical nova explosion must have been quite spectacular. "During that eruption," they write, "it must have become, for a few days or weeks, one of the brightest stars in the sky."

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages the mission and built the science instrument. JPL is a division of Caltech. The Galaxy Evolution Explorer mission was developed under NASA's Explorer Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

Media contact: Jane Platt (818) 354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

2007-023

Source: NASA - Missions - Galex

[Waspie_Dwarf]

Scene of Multiple Explosions

Z Camelopardalis, a double-star system featuring a collapsed, dead star, and a companion star, as well as a ghostly shell around the system

This composite image shows Z Camelopardalis, or Z Cam, a double-star system featuring a collapsed, dead star, called a white dwarf, and a companion star, as well as a ghostly shell around the system. The massive shell provides evidence of lingering material ejected during and swept up by a powerful classical nova explosion that occurred probably a few thousand years ago.

The image combines data gathered from the far-ultraviolet and near-ultraviolet detectors on NASA's Galaxy Evolution Explorer on Jan. 25, 2004. The orbiting observatory first began imaging Z Cam in 2003.

Z Cam is the largest white object in the image, located near the center. Parts of the shell are seen as a lobe-like, wispy, yellowish feature below and to the right of Z Cam, and as two large, whitish, perpendicular lines on the left.

Z Cam was one of the first known recurrent dwarf nova, meaning it erupts in a series of small, "hiccup-like" blasts, unlike classical novae, which undergo a massive explosion. That's why the huge shell around Z Cam caught the eye of astronomer Dr. Mark Seibert of Carnegie Institution of Washington in Pasadena, Calif. -- it could only be explained as the remnant of a full-blown classical nova explosion. This finding provides the first evidence that some binary systems undergo both types of explosions. Previously, a link between the two types of novae had been predicted, but there was no evidence to support the theory.

The faint bluish streak in the bottom right corner of the image is ultraviolet light reflected by dust that may or may not be related to Z Cam. Numerous foreground and background stars and galaxies are visible as yellow and white spots. The yellow objects are strong near-ultraviolet emitters; blue features have strong far-ultraviolet emission; and white objects have nearly equal amounts of near-ultraviolet and far-ultraviolet emission.

Image credit: NASA/JPL-Caltech

+ Full resolution TIFF (9Mb)

Source: NASA - Missions - Galex

[Waspie_Dwarf]

Ghostly Remnant of an Explosive Past

This enhanced image from the far-ultraviolet detector on NASA's Galaxy Evolution Explorer shows a ghostly shell of ionized gas around Z Camelopardalis, a binary, or double-star system featuring a collapsed, dead star known as a white dwarf, and a companion star.

The image was processed to enhance the diffuse emissions from the shell. Z Cam is the bright object near the center of the image. Parts of the shell are seen as a lobe-like, light-blue feature below and to the right of Z Cam, and as two large, light blue, perpendicular lines on the left.

The massive shell around Z Cam provides evidence of material ejected during and swept up by a powerful nova eruption, called a classical nova, which likely occurred a few thousand years ago.

In exploding binary systems, one of the two stars steals material from the other until it builds up to a certain level; at that point, the system erupts in a giant inferno. In the case of Z Cam, the white dwarf is pilfering material from its sedate companion.

There are two classes of exploding binary star systems, or cataclysmic variables: recurrent dwarf novae, which erupt in small, "hiccup-like" blasts episodically, and classical novae, which undergo huge explosions thousands of times more powerful than dwarf novae.

Z Cam was the one of the first known recurrent dwarf novae. Yet the shell of ionized gas around Z Cam detected by the Galaxy Evolution Explorer can only be explained as the remnant of a full-blown classical nova explosion. The discovery of the shell provides the first evidence that some binary systems undergo both types of explosions. Previously, a link between the two types of novae had been predicted, but there was no evidence to support the theory.

The Galaxy Evolution Explorer first began imaging Z Cam in 2003; this image was taken on Jan. 25, 2004. The type of emission found around Z Cam is most easily visible at far-ultraviolet wavelengths.

Most of the background galaxies and stars have been eliminated by the image processing, although a few linger as white spots near the top. The light-blue streaky clump in the bottom right corner is created by ultraviolet light reflected by dust. It is uncertain if Z Cam is the source of the dust-scattered light.

Image credit: NASA/JPL-Caltech

+ Full resolution TIFF (9Mb)

Source: NASA - Missions - Galex

[Waspie_Dwarf]

'That's Hot!' Galex Celebrates Four Years in Space

NASA's Galaxy Evolution Explorer is celebrating its fourth year in space with some of M81's "hottest" stars.

In a new ultraviolet image, the magnificent M81 spiral galaxy is shown at the center. The orbiting observatory spies the galaxy's "sizzling young starlets" as wisps of bluish-white swirling around a central golden glow. The tints of gold at M81's center come from a "senior citizen" population of smoldering stars.

"This is a spectacular view of M81," says Dr. John Huchra, of the Harvard Smithsonian Center for Astrophysics, Cambridge, Mass. "When we proposed to observe this galaxy with Galex we hoped to see globular clusters, open clusters, and young stars -- this view is everything that we were hoping for."

The image is one of thousands gathered so far by Galex, which launched April 28, 2003. This mission uses ultraviolet wavelengths to measure the history of star formation 80 percent of the way back to the Big Bang.

The large fluffy bluish-white material to the left of M81 is a neighboring galaxy called Holmberg IX. This galaxy is practically invisible to the naked human eye. However, it is illuminated brilliantly in Galex's wide ultraviolet eyes. Its ultraviolet colors show that it is actively forming young stars. The bluish-white fuzz in the space surrounding M81 and Holmberg IX is new star formation triggered by gravitational interactions between the two galaxies. Huchra notes that the active star formation in Holmberg IX is a surprise, and says that more research needs to be done in light of the new findings from Galex.

"Some astronomers suspect that the galaxy Holmberg IX is the result of a galactic interaction between M81 and another neighboring galaxy M82," says Huchra. "This particular galaxy is especially important because there are a lot of galaxies like Holmberg IX around our Milky Way galaxy. By understanding how Holmberg IX came to be, we hope to understand how all the little galaxies surrounding the Milky Way developed."

"Four years after Galex's launch, the spacecraft is performing magnificently. The mission results have been simply amazing as it helps us to unlock the secrets of galaxies, the building blocks of our universe," says Kerry Erickson, Galex project manager.

M81 and Holberg IX are located approximately 12 million light-years away in the northern constellation Ursa Major. In addition to leading the Galex observations of M81, Huchra and his team also took observations of the region with NASA's Spitzer and Hubble space telescopes. By combining all these views of M81, Huchra hopes to gain a better understanding about how M81 has developed into the spiral galaxy we see today.

Image credit: NASA/JPL-Caltech

+ High resolution JPEG (1Mb)

Source: NASA - Missions - Galex

[Waspie_Dwarf]

Galaxy Evolution Explorer Spies Band of Stars

The Galaxy Evolution Explorer's ultraviolet eyes have captured a globular star cluster, called NGC 362, in our own Milky Way galaxy. In this new image, the cluster appears next to stars from a more distant neighboring galaxy, known as the Small Magellanic Cloud.

"This image is so interesting because it allows a study of the final stages of evolution of low-mass stars in NGC 362, as well as the history of star formation in the Small Magellanic Cloud," said Ricardo Schiavon of the University of Virginia, Charlottesville, Va.


Image above: TGlobular star cluster NGC 362,
in a false-color image from NASA's Galaxy
Evolution Explorer.
Image credit: NASA/JPL-Caltech/
Univ. of Virginia
+ Browse version of image

Globular clusters are densely packed bunches of old stars scattered in galaxies throughout the universe. NGC 362, located 30,000 light-years away, can be spotted as the dense collection of mostly yellow-tinted stars surrounding a large white-yellow spot toward the top-right of this image. The white spot is actually the core of the cluster, which is made up of stars so closely packed together that the Galaxy Evolution Explorer cannot see them individually.

The light blue dots surrounding the cluster core are called extreme horizontal branch stars. These stars used to be very similar to our sun and are nearing the end of their lives. They are very hot, with temperatures reaching up to about four times that of the surface of our sun (25,000 Kelvin or 45,500 degrees Fahrenheit).

A star like our sun spends most of its life fusing hydrogen atoms in its core into helium. When the star runs out of hydrogen in its core, its outer envelope will expand. The star then becomes a red giant, which burns hydrogen in a shell surrounding its inner core. Throughout its life as a red giant, the star loses a lot of mass, then begins to burn helium at its core. Some stars will have lost so much mass at the end of this process, up to 85 percent of their envelopes, that most of the envelope is gone. What is left is a very hot ultraviolet-bright core, or extreme horizontal branch star.

Blue dots scattered throughout the image are hot, young stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way located approximately 200,000 light-years away. The stars in this galaxy are much brighter intrinsically than extreme horizontal branch stars, but they appear just as bright because they are farther away. The blue stars in the Small Magellanic Cloud are only about a few tens of millions of years old, much younger than the approximately 10-million-year-old stars in NGC 362.

Because NGC 362 sits on the northern edge of the Small Magellanic Cloud galaxy, the blue stars are denser toward the south, or bottom, of the image.

Some of the yellow spots in this image are stars in the Milky Way galaxy that are along this line of sight. Astronomers believe that some of the other spots, particularly those closer to NGC 362, might actually be a relatively ultraviolet-dim family of stars called "blue stragglers." These stars are formed from collisions or close encounters between two closely orbiting stars in a globular cluster.

"This observation could only be done with the Galaxy Evolution Explorer because it is the only ultraviolet imager available to the astronomical community with such a large field of view," said Schiavon.

This image is a false-color composite, where light detected by the Galaxy Evolution Explorer's far-ultraviolet detector is colored blue, and light from the telescope's near-ultraviolet detector is red.

Written by Linda Vu, Spitzer Science Center
Media contact: Whitney Clavin/JPL
(818) 354-4673

Source: NASA - Missions - Galex

[Waspie_Dwarf]

Galactic Nature vs. Nurture

Written by Linda Vu (Spitzer Science Center)
September 25, 2007

Just as psychologists have pondered the age-old question of "nature vs. nurture" in humans, astronomers are tackling a similar cosmic dilemma -- how much of a galaxy's development is due to innate characteristics, and how much is affected by the surrounding environment?

Now, astronomers using NASA's Galaxy Evolution Explorer (GALEX) hope that a rare sighting -- a spiral galaxy being stripped of its star forming material -- may give them some insights into this age-old question.


NGC 4522
Credit: NASA/JPL-Caltech/Yale University/H. Crowl (Yale University)

"Astronomers typically see spiral galaxies that are gas-rich and actively forming stars, or quiescent galaxies that are gas-poor and no longer forming starsÉ to see a galaxy like NGC 4522 in the process of being stripped of its star forming material is very rare," says Dr. Hugh Crowl, of Yale University, New Haven, Conn.

"This observation presents a perfect opportunity to study how a galaxy's environment affects its evolution."

No galaxy is an island. Almost every galaxy in the universe has a galactic "posse." Astronomers widely agree that interactions between galaxies play a significant role in how a particular galaxy develops. Some believe that galaxies start out as gas-rich spirals, active in star formation. Overtime, interactions with its cosmic environment literally knock the star forming gas out of the spiral galaxy, transforming it into an inactive disk that no longer forms stars.

Meanwhile, Crowl notes that innate phenomena like supernova explosions, and strong winds from black holes and massive stars, also play a significant role in pushing star forming materials out of a galaxy.

"This is an area of ongoing research, we still do not fully understand the extent to which various physical mechanisms are important for the stripping of star forming material from galaxies," he says.

In the case of NGC 4522, Crowl suspects that the galaxy's environment is currently playing a primary role in its development. He thinks that hot-gas surrounding the NGC 4522 is shoving the star forming material out of the galaxy's outer disk in a process astronomers call, "ram-pressure stripping."

Using the ground-based Very Large Array in New Mexico, CrowlÕs collaborators noticed that NGC 4522's outer disk lacked star forming materials. In addition, a large tail of neutral hydrogen was detected trailing the galaxy. Intrigued, he pointed GALEX's ultraviolet eyes at the galaxy and noticed a relatively young population of hot stars --approximately 100 million years old. Based on these observations, he concluded that the star forming gas and dust in the galaxy's outer disk must have been pushed out within the last hundred million years.

"GALEX is essentially seeing the last generation of stars that will ever form in NGC 4522's outer disk. Seeing those stars is important because they act as an age marker. From this population we can tell when the galaxy had its last episode of star formation and when it stopped forming stars altogether. The age of these stars tells us that NGC 4522 was stripped of its star forming gas at its current location, far from the core of the cluster. This suggests that some galaxies can be stripped in the outskirts of clusters," says Crowl.

"Since the galaxy's outer disk has been stripped of dust, there is nothing blocking our view of ultraviolet starlight. In this sense, GALEX offers us a clear view of NGC 4522's hot, young stars," he adds.

Crowl notes that his next goal is to expand his research to more galaxies.

NGC 4522 is located approximately 100 million light-years away in the Virgo cluster of galaxies. Crowl authored a paper on NGC 4522, which was published in the October 2006 issue of Astrophysical Journal Letter.

Dr. Jeffrey Kenney, also of Yale, was a co-author of the paper. Kenney led the observations of NGC 4522 with New Mexico's Very Large Array.

Source: Galex/Caltech

[Waspie_Dwarf]

NGC 4522 Stripped

Credit: NASA/JPL-Caltech/Yale University/H. Crowl (Yale University)

This image from NASA's Galaxy Evolution Explorer shows galaxy NGC4522 being stripped of its star-forming material. Astronomers refer to this process as "ram-pressure stripping" - where surrounding hot-gas shoves star-forming gas out of the galaxy's outer disk. NGC 4522 is located approximately 50 million light-years away in the Virgo galaxy cluster.

In this image, the galaxy's older stellar population is marked by tints of yellow. Meanwhile, the bluish-white ridge near NGC 4522's center reveals a population of very young stars - most likely less than a million years old. The bluish-white coloration also indicates that new stars are actively forming in this area.

The light-blue haze beyond the white-ridge represents the galaxy's outer disk. This area is currently not a site of active star formation, but is still very bright in the ultraviolet, indicating that some stars in this region are very young and likely formed very recently, within the last 50-100 million years.

This image is a three color composite where yellow represents R-band visible-light data from the Kitt Peak National Observatory's 0.9-meter telescope. Green shows near-ultraviolet light data, and blue reveals far-ultraviolet light data from GALEX.


About the data

• Field of view: 7x7 arcmin
• Orientation: North is up
• Color Mapping: GALEX - FUV (blue), NUV (cyan); Kitt Peak National Observatory (KPNO) 0.9m telescope - R-band/red (orange)
• Other notes: R-band KPNO data was taken by Dr. Rebecca Koopman (Union College), Jeffrey Kenney (Yale University), and Judith Young (University of Massachusetts)
• Reference: : 2001 ApJS,135, 125

Source: Galex/Caltech

[Waspie_Dwarf]

Watching Galaxies Grow Old Gracefully

11.14.07

In the early 1900s, Edwin Hubble made the startling discovery that our Milky Way galaxy is not alone. It is just one of many galaxies, or "island universes," as Hubble dubbed them, swimming in the sea of space.

Now, a century later, NASA's Galaxy Evolution Explorer is helping piece together the evolution of these cosmic species. Since its launch in 2003, the mission has surveyed tens of thousands of galaxies in ultraviolet light across nine billion years of time. The results provide new, comprehensive evidence for the "nurture" theory of galaxy evolution, which holds that the galaxies first described by Hubble – the elegant spirals and blob-like ellipticals -- are evolutionarily linkeds.


Image right: Examples of young, teenage and adult galaxies are shown here from left to right.
Image credit: NASA/JPL-Caltech

According to this "nurture" theory, a typical young galaxy begins life as a spiral that is actively churning out stars. Over time, the spiral might merge with another spiral or perhaps an irregular-shaped galaxy, before kicking out a few more bursts of newly minted stars. Eventually, the galaxy slows down its production of stars and settles into later life as an elliptical.

"Our data confirm that all galaxies begin life forming stars," said Chris Martin, the principal investigator for the Galaxy Evolution Explorer at the California Institute of Technology in Pasadena, Calif. "Then through a combination of mergers, fuel exhaustion and perhaps suppression by black holes, the galaxies eventually stop producing stars."

When astronomers talk about galaxies today, they tend to refer to them by their color, either blue or red, instead of by their shape. Most blue galaxies are smaller spirals or irregulars, and most red galaxies are larger ellipticals, though there are some exceptions.

Why color-code the galaxies? Their color indicates how actively they are making new stars. Younger stars shine in ultraviolet or blue light, so galaxies that appear blue are busily producing stars. Older stars emit infrared or red light, so galaxies that look red have shut down their star-making factories. Roughly half of all galaxies are blue and half are red.

Scientists have long postulated that blue galaxies grow up to become red. They proposed that something happens to the blue galaxies to cause them to run out of star-making material, or gas, and mature into the passive red ones. For this "nurture" theory to be true, there should be a population of "teenage" galaxies in the process of transitioning from blue to red, or young to old. But such a cosmic metamorphosis should take billions of years. How can astronomers, with a significantly shorter lifespan, study a process that takes that long?

One solution is to look at lots and lots of galaxies. Imagine a hypothetical alien trying to figure out how and if humans age from only a handful of snapshots showing people of different ages. The aliens might assume that little people grow into big ones, but they could better piece together the life of a typical human if they could look through boxes and boxes of photographs.

The Galaxy Evolution Explorer was designed to provide astronomers with just such a massive portfolio of galaxies. Its troves of data have allowed scientists to find a significant number of teenage galaxies – and thus proof that youthful spiral, or blue, galaxies will eventually grow up to become the elderly elliptical, or red, galaxies.

"The nurture theory of galaxy evolution predicted that there would be galaxies in transition," said Martin. "Finding these galaxies required ultraviolet light, because they really stand out at this wavelength. And because they are rare, we had to look at many. The Galaxy Evolution Explorer allowed us to do this."

Visible-light data from the Sloan Digital Sky Survey also helped to establish the age of the teenage galaxies and the rates at which they are running out of star-making fuel. These findings suggest that some of the young galaxies are ripening into old age quickly, while others are leisurely strolling into their golden years.

Evidence for the "nurture" theory of galaxy evolution can be found in a report in the Astrophysical Journal. Martin is the lead author.

Graphics and additional information about the Galaxy Evolution Explorer are online at _http://www.nasa.gov/galex and _http://www.galex.caltech.edu.

Media contact: Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673 whitney.clavin@jpl.nasa.gov

Source: NASA - Missions - Galex

[Waspie_Dwarf]

Portrait of a Galaxy's Life

11.14.07

+ High resolution image (1.5Mb)

New evidence from NASA's Galaxy Evolution Explorer supports the long-held notion that many galaxies begin life as smaller spirals before transforming into larger, elliptical-shaped galaxies.

Examples of young, teenage and adult galaxies are shown here from left to right. The data making up these photos come from both the Galaxy Evolution Explorer and visible-light telescopes. Long-wavelength ultraviolet light is blue; short-wavelength ultraviolet light is green; and visible red light is red.

The galaxy on the left is NGC 300, a spiral located about seven million light-years away in the constellation Sculptor. Younger galaxies like this one tend to form more stars, and since new stars give off more ultraviolet and blue light, the galaxies appear blue.

The galaxy on the right is NGC 1316, located about 62 million light-years away in the constellation Fornax. It is an older elliptical. Older stars emit more red light, so this galaxy appears red.

The galaxies in the middle of the diagram represent the teenagers, which are on their way from becoming blue to red. The relatively small patches of ultraviolet light in these transitional galaxies indicate that star formation is winding down. The galaxy at center left is NGC 4569, located about four million light-years away in the constellation Virgo. The galaxy at center right is NGC 1291, located about 33 million light-years away in the constellation Eradinus.

Before the Galaxy Evolution Explorer launched more than four years ago, there weren't a lot of examples of transitional galaxies, which made it difficult to demonstrate that galaxies mature from blue to red. The Galaxy Evolution Explorer allowed astronomers to find good examples of these elusive teenagers through its extensive catalogue of tens of thousands of galaxies photographed in ultraviolet light.

NGC 300 image credit: NASA/JPL-Caltech/Las Campanas Observatory

NGC 4569 image credit: NASA/JPL-Caltech/Palomar 1.5m

NGC 1291 image credit: NASA/JPL/CTIO

NGC 1316 image credit: NASA/JPL-CTIO

Source: NASA - Missions - Galex

[Waspie_Dwarf]

NGC 300

11.14.07

+ Larger image

This image from NASA's Galaxy Evolution Explorer shows the galaxy NGC 300, located about seven million light-years away in the constellation Sculptor. It is a classic spiral galaxy with open arms and vigorous star formation throughout.

Blue represents ultraviolet light captured by the telescope's long-wavelength detector. Green shows ultraviolet light from the short-wavelength detector, and red shows red visible light from the Las Campanas Observatory, Chile.

The Galaxy Evolution Explorer data was taken in October 2003.

Image credit: NASA/JPL-Caltech/Las Campanas

Source: NASA - Missions - Galex

[Waspie_Dwarf]

NGC 1291

11.14.07

+ Larger image

This image from NASA's Galaxy Evolution Explorer shows the galaxy NGC 1291, located about 33 million light-years away in the constellation Eradinus. NGC 1291 is notable for its unusual inner bar and outer ring structure.

Blue represents ultraviolet light captured by the telescope's long-wavelength detector. Green shows ultraviolet light from the short-wavelength detector, and red shows red visible light from the Cerro Tololo Inter-American Observatory, Chile.

The Galaxy Evolution Explorer data was taken in December 2003.

Image credit: NASA/JPL-Caltech/CTIO

Source: NASA - Missions - Galex

[Waspie_Dwarf]

NGC 4569

11.14.07

+ Larger image

This image from NASA's Galaxy Evolution Explorer shows the galaxy NGC 4569, located about four million light-years away in the constellation Virgo. It is one of the largest and brightest spiral galaxies found in the Virgo cluster of galaxies, the nearest major galaxy cluster to our Milky Way galaxy.

Blue represents ultraviolet light captured by the telescope's long-wavelength detector. Green shows ultraviolet light from the short-wavelength detector, and red shows red visible light from the Palomar 1.5-meter telescope, near San Diego.

The Galaxy Evolution Explorer data was taken in March 2004.

Image credit: NASA/JPL-Caltech/Palomar

Source: NASA - Missions - Galex

[Waspie_Dwarf]

NGC 1316

11.14.07

+ Larger image

This image from NASA's Galaxy Evolution Explorer shows the galaxy NGC 1316, located about 62 million light-years away in the constellation Fornax. The elliptical-shaped galaxy may be in the late stages of merging with a smaller companion galaxy.

Blue represents ultraviolet light captured by the telescope's long-wavelength detector. Green shows ultraviolet light from the short-wavelength detector, and red shows red visible light from the Cerro Tololo Inter-American Observatory, Chile.

The Galaxy Evolution Explorer data was taken in December 2003.

Image credit: NASA/JPL-Caltech/CTIO

Source: NASA - Missions - Galex

[thefinalfrontier]

From Nasa's galaxy evolution explorer mission known as GALEX

The "Ghost of Mirach" galaxy is shown in visible light on the left, and in ultraviolet as seen by NASA's Galaxy Evolution Explorer on the right. The fields of view are identical in both pictures, with the Ghost of Mirach -- a galaxy called NGC 404 -- seen as the whitish spot in the center of the images. Mirach is a red giant star that looms large in visible light. Because NGC 404 is lost in the glare of this star, it was nicknamed the Ghost of Mirach.

But when the galaxy is viewed in ultraviolet light, it comes to "life," revealing a never-before-seen ring. This ring, seen in blue in the picture on the right, contains new stars -- a surprise considering that the galaxy was previously thought to be, essentially, dead.

The field of view spans 55,000 light years across. The Ghost of Mirach is located 11 million light-years from Earth. The star Mirach is very close in comparison -- it is only 200 light-years away and is visible with the naked eye.

The visible data come from the Digitized Sky Survey of the Space Telescope Science Institute in Baltimore, Md.

Source: Galex web site

Edited April 12, 2010 by Waspie_Dwarf
added source link.

[schizoidwoman]

New stars in a dead galaxy? There are some really amazing discoveries happening at the moment!

[fenris1011]

Wow.

[Waspie_Dwarf]

Astronomers Discover Star-Studded Galaxy Tail

06.17.10

NASA's Galaxy Evolution Explorer found

a tail behind a galaxy called IC 3418.

The star-studded tail can be seen in the

image on the left, as detected by the

space telescope in ultraviolet light. The

tail has escaped detection in visible light,

as shown by the image on the right.

Credit: NASA/JPL-Caltech

› Larger image

NASA's Galaxy Evolution Explorer has discovered a galaxy tail studded with bright knots of new stars. The tail, which was created as the galaxy IC 3418 plunged into the neighboring Virgo cluster of galaxies, offers new insight into how stars form.

"The gas in this galaxy is being blown back into a turbulent wake," said Janice Hester of the California Institute of Technology in Pasadena, lead author of a recent study published in the Astrophysical Journal Letters. "The gas is like sand caught up by a stiff wind. However, the particular type of gas that is needed to make stars is heavier, like pebbles, and can't be blown out of the galaxy. The new Galaxy Evolution Explorer observations are teaching us that this heavier, star-forming gas can form in the wake, possibly in swirling eddies of gas."

Collisions between galaxies are a fairly common occurrence in the universe. Our Milky Way galaxy will crash into the Andromeda galaxy in a few billion years. Galaxies tangle together, kicking gas and dust all around. Often the battered galaxies are left with tails of material stripped off during the violence.

Hester and her team studied the tail of IC 3418, which formed in a very different way. IC 3418 is mingling not with one galaxy, but with the entire Virgo cluster of galaxies 54 million light-years away from Earth. This massive cluster, which contains about 1,500 galaxies and is permeated by hot gas, is pulling in IC 3418, causing it to plunge through the cluster's gas at a rate of 1,000 kilometers per second, or more than 2 million miles per hour. At this incredible speed, the little galaxy's gas is being shoved back into a choppy tail.

The astronomers were able to find this tail with the help of the Galaxy Evolution Explorer. Clusters of massive, young stars speckle the tail, and these stars glow with ultraviolet light that the space telescope can see. The young stars tell scientists that a crucial ingredient for star formation - dense clouds of gas called molecular hydrogen - formed in the wake of this galaxy's plunge. This is the first time astronomers have found solid evidence that clouds of molecular hydrogen can form under the violent conditions present in a turbulent wake.

"IC 3418's tail of star-formation demonstrates that strong turbulence promotes cloud formation," said Mark Seibert, a co-author of the paper and a member of the Galaxy Evolution Explorer science team at the Carnegie Institute for Science in Pasadena.

Hester added that galaxy tails provide the perfect environment for isolating the factors controlling star formation.

"These tails are unique, exotic locations where we can probe the precise mechanisms behind star formation," said Hester. "Understanding star formation is pivotal to understanding the lifecycles of galaxies and the dramatic transformations that some galaxies undergo. We can also study how the process affects the development of planets like our own."

Other authors of the paper are James D. Neill, Ted K. Wyder and Christopher Martin of Caltech; Armando Gil de Paz of the Universidad de Computense de Madrid, Spain; Barry F. Madore of the Carnegie Institute of Washington; David Schiminovich of Columbia University, N.Y., N.Y; and Michael Rich of UCLA.

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission. 


Graphics and additional information about the Galaxy Evolution Explorer is online at http://www.nasa.gov/galex/ and http://www.galex.caltech.edu.


Whitney Clavin

(818) 354-4673

Whitney.clavin@jpl.nasa.gov

2010-202

Source: NASA - Missions - Galex