Universe Today

Image credit: Chandra

The Chandra X-Ray Observatory has found rich deposits of neon, magnesium and silicon in a pair of colliding galaxies called The Antennae, located 30 million light-years away. When these hot clouds eventually cool, they’ll serve as enormous nurseries for newborn stars. Astronomers are interested in this collision because it’s very similar to what will happen when the Milky Way and Andromeda galaxies collide in about 3 billion years.

NASA’s Chandra X-ray Observatory has discovered rich deposits of neon, magnesium, and silicon in a pair of colliding galaxies known as The Antennae. When the clouds in which these elements are present cool, an exceptionally high number of stars with planets should form. These results may foreshadow the fate of the Milky Way and its future collision with the Andromeda Galaxy.

“The amount of enrichment of elements in The Antennae is phenomenal,” said Giuseppina Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. at a press conference at a meeting of the American Astronomical Society in Atlanta, Ga. “This must be due to a very high rate of supernova explosions in these colliding galaxies.” Fabbiano is lead author of a paper on this discovery by a team of U.S. and U.K. scientists that will appear in an upcoming issue of The Astrophysical Journal Letters.

When galaxies collide, direct hits between stars are extremely rare, but collisions between huge gas clouds in the galaxies can trigger a stellar baby boom. The most massive of these stars race through their evolution in a few million years and explode as supernovas. Heavy elements manufactured inside these stars are blown away by the explosions and enrich the surrounding gas for thousands of light years.

“The amount of heavy elements supports earlier studies that indicate there was a very high rate of relatively recent supernovas, 30 times that of the Milky Way,” according to collaborator Andreas Zezas of the CfA.

The supernova violence also heats the gas to millions of degrees Celsius. This makes much of the matter in the clouds invisible to optical telescopes, but it can be observed by an X-ray telescope. Chandra data revealed for the first time regions of varying enrichment in the galaxies ? in one cloud magnesium and silicon are 16 and 24 times as abundant as in the Sun.

“These are the kinds of elements that form the ultimate building blocks for habitable planets,” said Andrew King of the University of Leicester, U.K. and a coauthor of the study. “This process occurs in all galaxies, but it is greatly enhanced by the collision. Usually we only see the new elements in diluted form as they are mixed up with the rest of the interstellar gas.”

CfA coauthor Alessandro Baldi commented that, “This is spectacular confirmation of the idea that the basis of chemistry, of planets, and ultimately of life is assembled inside stars and spread through galaxies by supernova explosions,”

As the enriched gas cools, a new generation of stars will form, and with them new planets. A number of studies indicate that clouds enriched in heavy elements are more likely to form stars with planetary systems, so in the future an unusually high number of planets may form in The Antennae.

“If life arises on a significant fraction of these planets, then in the future the Antennae will be teeming with life,” speculated Francois Schweizer, another coauthor who is from the Carnegie Observatories in Pasadena, Calif. “A vast number of Sun like stars and planetary systems will age in unison for billions of years.”

At a distance of about 60 million light years, The Antennae system is the nearest example of a collision between two large galaxies. The collision, which began a couple of hundred million years ago, has been so violent that gas and stars from the galaxies have been ejected into the two long arcs that give the system its name. The Chandra image shows spectacular loops of 3-million-degree gas spreading out south of the antennae. “These loops may be carrying out some of the elements dispersed by supernovas into intergalactic space,” said Trevor Ponman of Birmingham University, U.K.

The Antennae give a closeup view of the type of collisions that were common in the early universe and likely led to the formation of most of the stars that exist in the universe today. They may also provide a glimpse of the future of our Milky Way Galaxy, which is on a collision course with the Andromeda Galaxy. At the present rate, a crash such as the one now occurring in the Antennae could happen in about 3 billion years. Tremendous gravitational forces will disrupt both galaxies and reform them, probably as a giant elliptical galaxy with hundreds of millions of young Sun like stars, and possibly planetary systems.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release

Image credit: NASA/JPL

Now that it’s survived its dangerous journey through the tail of Comet Wild-2, NASA’s Stardust spacecraft is heading for home. On board is its precious cargo of comet fragments that will be returned to Earth in 2006 for analysis by scientists. Even though the spacecraft’s camera was only really designed for navigation, it took 72 photographs which are some of the best images of a comet ever taken. Scientists hope that the cometary particles will help answer questions about the earliest history of our solar system.

Having weathered its out-of-this-world sandblasting by cometary particles hurtling toward it at about six times the speed of a rifle bullet, NASA’s Stardust spacecraft begins its two-year, 1.14 billion kilometer (708 million mile) trek back to its planet of origin.

“On January 2, comet Wild 2 gave up its particles but it did not do so without a fight,” said Stardust Project Manager Tom Duxbury of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Our data indicates we flew through sheets of cometary particles that jostled the spacecraft and that on at least 10 occasions the first layer of our shielding was breeched. Glad we had a couple more layers of the stuff.”

Stardust entered the comet’s coma ? the vast cloud of dust and gas that surrounds a comet’s nucleus – on December 31, 2003. From that point on it kept its defensive shielding between it and what scientists hoped would be the caustic stream of particles it would fly through. And fly through cometary particles Stardust did, but not in the fashion the team envisioned while designing the mission.

“We thought we would see a uniform increase in the number of particles the closer we came to the comet’s nucleus and then a reduction,” said University of Washington scientist Dr. Don Brownlee, Stardust’s Principal Investigator. “Instead, our data indicate we flew through a veritable swarm of particles and then there would be almost nothing and then we would fly through another swarm.”

Stardust scooped up these cometary particles, impacting at 6.1 kilometers per second (3.8 miles per second), for almost instantaneous analysis from onboard instruments and stored other particles for later, in-depth analysis, here on Earth. Along with this cosmic taste testing, the spacecraft also took some remarkable images of comet Wild 2’s five-kilometer wide (3.1- mile wide) nucleus.

“Our navigation camera was designed to assist in navigation, not science,” said Stardust’s imaging team lead Ray Newburn. “But these are the best images ever taken of a comet and there is a remarkable amount of information in those 72 pictures. Not only did we image the jets of material spewing out from the comet, but for the first time in history we can actually see the location of their origin on the surface of the comet.”

At about 11:25 am Pacific Standard Time (2:25pm EST) on Jan. 2, only minutes after its closest approach with the comet, Stardust pointed its high gain antenna at Earth and began transmitting a data stream that took over 30 hours to send but will keep cometary scientists busy for years to come. About six hours later another event took place that goes a long way to literally increasing the scientists task load exponentially.

“Six hours after encounter we retracted the collector grid, with what we are all confident is an abundance of cometary particles, into the spacecraft’s sample return capsule,” added Duxbury. “The next time the sample return capsule is going to be opened is in a clean room at the Johnson Space Center in the days following Earth return in January 2006.”

Scientists expect in-depth terrestrial analysis of the samples will reveal much about comets and the earliest history of the solar system. Chemical and physical information locked within the particles could be the record of the formation of the planets and the materials from which they were made. More information on the Stardust mission is available at http://stardust.jpl.nasa.gov.

Stardust, a part of NASA’s Discovery Program of low-cost, highly focused science missions, was built by Lockheed Martin Space Systems, Denver, Colo., and is managed by JPL for NASA’s Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.

Original Source: NASA/JPL News Release

Image credit: Chandra

A new image from the Chandra X-Ray Observatory shows a distant galaxy that used to look like our own Milky Way crashing into a cluster of galaxies at 7.5 million kilometers per hour. The force of this collision is so strong that the ambient hydrogen in the galaxy is being stripped away, leaving only the skeletal spiral arms. Without hydrogen, new star formation in the galaxy has come to a stop. Although galaxy collisions have been seen before, this is the most swift and violent one ever seen.

Trailing 200,000-light-year-long streamers of seething gas, a galaxy that was once like our Milky Way is being shredded as it plunges at 4.5 million miles per hour through the heart of a distant cluster of galaxies. In this unusually violent collision with ambient cluster gas, the galaxy is stripped down to its skeletal spiral arms as it is eviscerated of fresh hydrogen for making new stars.

The galaxy’s untimely demise is offering new clues to solving the mystery of what happens to spiral galaxies in a violent universe. Views of the early universe show that spiral galaxies were once much more abundant in rich clusters of galaxies. But they seem to have been vanishing over cosmic time. Where have these “missing bodies” gone?

Astronomers are using a wide range of telescopes and analysis techniques to conduct a “CSI” or Crime Scene Investigator-style look at what is happening to this galaxy inside its cluster’s rough neighborhood. “It’s a clear case of galaxy assault and battery,” says William Keel of the University of Alabama. “This is the first time we have a full suite of results from such disparate techniques showing the crime being committed, and the modus operandi.”

Keel and colleagues are laying out the “forensic evidence” of the galaxy’s late life, in a series of presentations today in Atlanta, Ga., at the 203rd meeting of the American Astronomical Society. Astronomers have assembled the evidence by combining a variety of diagnostic observations from telescopes analyzing the galaxy’s appearance in X-ray, optical, and radio light. Parallel observations at different wavelengths trace how stars, gas, and dust are being tossed around and torn from the fragile galaxy, called C153. Though such “distressed” galaxies have been seen before, this one’s demise is unusually swift and violent. The galaxy belongs to a cluster of galaxies that slammed into another cluster about 100 million years ago. This galaxy took the brunt of the beating as it fell along a trajectory straight through the dense core of the colliding cluster.

“This helps explain the weird X-ray and radio emissions we see,” says Keel. “The galaxy is a laboratory for studying how gas can be stripped away when it flies through the hot cluster gas, shutting down star birth and transforming the galaxy.”

The first suggestion of galactic mayhem in this cluster came in 1994 when the Very Large Array radio telescope near Socorro, N.M., detected an unusual number of radio galaxies in the cluster, called Abell 2125. Radio sources trace both star formation and the feeding of central black holes in galaxy clusters. The radio observations also showed that C153 stood out from the other galaxies as an exceptionally powerful radio source.

Keel’s team began an extensive program of further observations to uncover details about the galaxies. “This was designed to see what the connection could possibly be between events on the 10-million-light-year scale of the cluster merger and what happens deep inside individual galaxies,” says Keel.

X-ray observations from the ROSAT satellite (an acronym for the Roentgen Satellite) demonstrated that the cluster contains vast amounts of 36-million-degree Fahrenheit (20-million-degree Kelvin) gas that envelops the galaxies. The gas is concentrated into two main lumps rather than smoothly distributed across the cluster, as is more commonly the case.

This bolstered the suspicion that two galaxy clusters are actually colliding. In the mid-to-late 1990s astronomers turned the Mayall 4-meter telescope and the WIYN 3.5-meter telescope at the Kitt Peak National Observatory on the cluster to analyze the starlight via spectroscopy. They found many star-forming systems and even active galactic black holes fueled by the collision. The disintegrating galaxy C153 stood out dramatically when the KPNO telescopes were used to photomap the cluster in color.

Astronomers then trained NASA’s Hubble Space Telescope (HST) onto C153 and resolved a bizarre shape. They found that the galaxy looks unusually clumpy with many young star clusters and chaotic dust features. Besides the disrupted features in the galaxy’s disk, HST also showed that the light in the tail is mostly attributed to recent star formation, providing a direct link to the stripping of the galaxy as it passed through the cluster core. Gas compressed along the galaxy’s leading edge, like snow before a plow, ignited a firestorm of new star birth. Evidence of recent star formation also comes from the optical spectrum obtained at the 10-meter Gemini North telescope in Hawaii. The spectrum allows the researchers to estimate the time since the most recent burst of star formation.

This conclusion was further bolstered when the Mosaic camera on Kitt Peak’s Mayall telescope found a very long tail of extended gas coming off the galaxy. The tail was apparently generated in part by a hurricane of stellar winds boiling off the new star-birth regions and being blown backwards as the galaxy streaks through the surrounding hot gas of the cluster.

Spectroscopic observations with the Gemini telescope allowed astronomers to age-date the starburst. They find that 90 percent of C153’s blue light is from a population of stars that are 100 million years old. This age corresponds to the time the galaxy should have gone careening through the densest gas in the cluster core.

The Gemini spectroscopic observations show the stars are in a regular pattern of orbital motion around the center, as usual for disk galaxies. However, there are multiple widespread clouds of gas moving independently of the stars. “This is an important clue that something beyond gravitational forces must be at work, since stars and gas respond the same way to purely gravitational forces,” says Keel. “In other words, the galaxy’s gas doesn’t know what the stars are doing.”

NASA’s Chandra X-ray Observatory discovered that the cooler clouds detected with optical telescopes and an associated radio feature are embedded in a much larger multimillion-degree trail of gas. Chandra’s data indicate that this hot gas was probably enriched in heavy elements by the starburst and driven out of the galaxy by its supersonic motion through the much larger cloud of gas that pervades the cluster.

Collectively, these observations offer evidence that the ram pressure of external gas in the cluster is stripping away the galaxy’s own gas. This process has long been hypothesized to account for the forced evolution of cluster galaxies. Its aftermath has been seen in several ways. Some nearby examples, Seyfert’s Sextet and Stefan’s Quintet, are tight clusters that show the aftermath of high-velocity collisions.

The galaxy C153 is destined to lose the last vestiges of its spiral arms and become a bland S0-type galaxy having a central bulge and disk, but no spiral-arm structure. These types of galaxies are common in the dense galaxy clusters seen today. Astronomers plan to make new observations with Gemini again in 2004 to study the dynamics of the gas and stars in the tail.

The science team members are William Keel (University of Alabama), Frazer Owen (National Radio Astronomy Observatory), Michael Ledlow (Gemini Observatory), and Daniel Wang (University of Massachusetts).

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release