M101 - A Pinwheel in X-rays

With a diameter of about 170,000 light years, the galaxy Messier 101 (M101) is a swirling spiral of stars, gas, and dust whose diameter is nearly twice that of our Milky Way Galaxy. Its orientation allows telescopes to see the spiral structure of the galaxy face-on, giving inspiration for its nickname of the Pinwheel Galaxy. M101 is found in the Ursa Major constellation and is at a distance of about 25 million light years from Earth.

This Chandra image of M101 is one of the longest exposures ever obtained of a spiral galaxy in X-rays. The point-like sources include binary star systems containing black holes and neutron stars, and the remains of supernova explosions. Other sources of X-rays include hot gas in the arms of the galaxy and clusters of massive stars. These X-ray observations of M101 will be used to establish a valuable X-ray profile of a galaxy similar to the Milky Way. This will help astronomers better understand the evolutionary paths that produce black holes, and provide a baseline for interpreting the observations of distant galaxies.

Chandra spies aftermath of galaxy collision

photo:This Chandra image of the elliptical galaxy NGC 4261 reveals dozens of black holes and neutron stars strung out like beads on a necklace across tens of thousands of light-years. The spectacular structure, which is not apparent from optical images of the galaxy, is thought to be the remains of a collision between galaxies a few billion years ago.The image covers 237 x 290 arcseconds. NASA / CXC / A. Zezas et al.

February 16, 2004

What do you get when two galaxies collide head-on? Astronomers believe the answer may lie just 100 million light-years away from Earth. Like the scene of a hit-and-run accident, a trail of cosmic debris has been left behind for investigators to sift through. Intense X-ray sources embedded in a 10th-magnitude elliptical galaxy called NGC 4261 point to a galaxy collision long ago.

With its high-resolution X-ray vision, NASA's Chandra space observatory has imaged this stellar wreckage of black holes and neutron stars spread over 50,000 light-years. The Hubble Space Telescope previously imaged NGC 4261, located in the constellation Virgo, revealing a supermassive black hole swirling in the heart of the galaxy. What Chandra saw for the first time, however, is the optically invisible signature of a violent fusion between two galaxies billions of years ago that created the single elliptical galaxy we see today. Whereas optical remnants of galaxy collisions vanish relatively quickly, their X-ray fingerprints linger for hundreds of millions of years.

"From the optical and radio images, we knew something unusual was going on in the nucleus of this galaxy, but the real surprise turned out to be on the outer edges of the galaxy," says Andreas Zezas of the Harvard-Smithsonian Center for Astrophysics (CfA) and lead author of this study. "Dozens of black holes and neutron stars were strung out across space like beads on a necklace."

Publishing their findings in an upcoming issue of The Astrophysical Journal Letters, the American team of astronomers believes Chandra's detection of a string of X-ray sources reveals the destruction of a small, interloper galaxy. Gravitational tidal forces produced when this galaxy was ripped apart likely created shock waves that swept through NGC 4621. These shock waves created large tails that triggered the formation of massive stars. Many of these heavyweights evolved into neutron stars and black holes, and those with stellar companions began to shine in X-rays as gas was sucked into their huge gravity wells.

Just how elliptical galaxies form has been the subject of much debate over the years. Theoretical models, computer simulations, and optical images of galactic tails, shells, ripples, arcs, and other structures all point to galaxy collisions and mergers.

"This discovery shows that X-ray observations may be the best way to identify the ancient remains of mergers between galaxies," explains co-investigator Lars Hernquist of CfA. Having observed with Chandra for 35 hours, Zezas and his colleagues argue their data is the best evidence yet for elliptical galaxy births.

X-ray image exposes dysfunctional galactic family

photo:X-ray observations by the Chandra X-ray Observatory appear in blue and are overlaid upon a yellow-colored optical image by the Digitized Sky Survey. The blue regions contain shock-heated gas that has a temperature of about 6 million degrees Celsius. The heating is produced by the rapid motion of a spiral galaxy intruder located immediately to the right of the shock wave in the center of the image. X-ray: NASA / CXC / INAF-Brera / G.Trinchieri et al.; Optical: Palomar Observatory / DSS

The members of Stephan's Quintet poke, swipe, and pull at each other, causing a lot of friction between themselves.

Kelly Kizer Whitt

May 17, 2003

The Chandra X-ray Observatory has imaged a shock wave between the tightly knit galaxies known as Stephan's Quintet. Optical images do not reveal the 6-million-degree-Celsius gas that was created when the spiral galaxy NGC 7318b punched through the area.

This is not the first time Stephan's Quintet has been punctured by a forceful galaxy. The x-ray image shows evidence that the small spiral galaxy NGC 7320c plowed through the region several hundred million years ago. This disruption created the tail of stars that leads away from the spiral galaxy NGC 7319. NGC 7320c may have intruded on the quintet more than once, and it is now keeping its distance 460,000 light-years from the others.

The brightest galaxy, NGC 7320, is only visually connected to the quintet by a line-of-sight coincidence. It actually lies 35 million light-years from Earth, whereas the other members all lie about 280 million light-years away. However, the group can still be counted a five-some when the frequent intruder NGC 7320c is included.

The chaotic movement of the galaxies and their gravitational pulls are removing cool gas, which is the raw material for the formation of new stars. Therefore, in a few billion years the spirals of Stephan's Quintet will settle into a rounded-out group of elliptical galaxies.

Stephan's Quintet may look familiar to the lay person because it is featured in the classic 1946 holiday movie It's a Wonderful Life as a group of conversing heavenly angels. Stephan's Quintet is the prototype of a compact group of galaxies and was discovered by French astronomer Edouard M. Stephan in 1877. He first spied the group with the 40-centimeter refracting telescope at the Observatory of Marseilles. Located in the constellation Pegasus, Stephan's Quintet is also known as Hickson 92, Arp 319, and VV 228.

Star-Eating Mass Found Near Center of Milky Way

20 September 1999

A brilliant X-ray outburst in the direction of the galactic center flared to prominence last Wednesday, turning a relatively sedate energy source into the brightest X-ray object in the sky.

Instruments aboard at least two X-ray observing spacecraft detected the flash, which was most likely produced by a huge mass of material being swallowed by a black hole or neutron star.The event has been tracked down to an area near a visible star called GM Sagittarii in the constellation Sagittarius.

That star is known to vary in brightness when observed at visible light, said Mike McCollough, a staff scientist at NASA's Marshall Space Flight Center. The existence of a high-energy X-ray source next to it means that the star is actually part of a system called an X-ray binary, a pair in which a star and an extremely dense object such as a neutron star or a black hole orbit each other, he said.

Last week's unusually energetic activity was first noticed Wednesday, said McCollough, who works on a team that analyzes data from the Burst and Transient Source Experiment (BATSE) instrument aboard the Compton Gamma Ray Observatory. That NASA spacecraft is designed to observe sources of high-energy radiation.

When McCollough heard that other instruments had detected the X-ray burst, he looked at information from the Compton instruments and noticed a brief, but huge spike in emissions from GM Sagittarii on Tuesday. The object -- which is typically some 30 times dimmer than the pulsar in the Crab nebula -- jumped to about five times brighter than that object before it dimmed again.

The Crab pulsar is usually the brightest X-ray object in the sky. It is the standard against which X-ray luminosity is commonly measured.

Sifting through data for Wednesday, McCollough found nothing for the first half of the day, he said.

"Then about 10 hours into the day we started seeing it go off. Literally within about six hours it got to about eight times the Crab," he said. "It essentially wasn't there and then it just went through the roof on us."

Meanwhile, scientists watching data from the Rossi X-ray Explorer (another spacecraft that observes X-rays) were witnessing the intense flare in X-ray emissions from Sagittarius, but at slightly less energetic X-ray wavelengths than BATSE picks up.

Within eight hours on Wednesday, Rossi scientists saw GM Sagittarii flare to more than 12 times brighter than the Crab nebula then drop just as dramatically, said William Heindl, a research scientist at the Center for Astrophysics and Space Science at the University of California at San Diego, who works with data from the Rossi observer.

The spacecraft's sky scanner measured most the activity, Heindl said, but scientists aimed the instrument's telescope into view just in time to see the object's last violent sputter -- the object had dimmed, then within a period of about 15 minutes, it flashed to about twice the brightness of the Crab before Earth obscured the spacecraft's view.

When Rossi next glimpsed GM Sagittarii, the object was quiet and dark, betraying no hint of its violent outburst, Heindl said.

The jolts in X-ray emissions both in the low-energy "soft" X-rays, measured by Rossi, and the higher-energy "hard" X-rays detected by BATSE mean that they were produced as material falls into either by a black hole or neutron star, McCollough said. The source of that material is probably the companion star that is feeding the black hole or neutron star.

Based on the new observations, the system will need to be reclassified as an X-ray binary, McCollough said. The system will likely attract a lot more attention in the coming year as scientists try to learn more about the star, its mass, and just what the high-density object beside it is, he said.


[ Important note: Due to a mix-up among astronomers, the star in this article is misidentified as GM Sagittarii. The star associated with the brilliant X-ray burst of September 15, 1999 is now called V 4641 Sagittarii. For two decades astronomers have been incorrectly calling V4641 by the name GM Sagittarii, a mistake which was recently discovered and announced on October 13, 1999. ]

Edge of Darkness: Milky Way's Black Hole 'Seen' in X-rays

Simulation of a supermassive black hole as seen from above. Hot, compressed gas swirls around the event horizon. Blue indicates the radio waves oscillating sideways; red indicates waves oscillating vertically. The bright, thin ring is due to light that has circled the black hole once before leaving its environment.

Scientists announced today some of the most compelling evidence to date for the existence of a colossal black hole at the center of the Milky Way Galaxy, also determining a new and much smaller upper limit to the diameter of the mysterious object.

Experts were already fairly sure that the black hole resided at the center of our galaxy, packing the mass of 2.6 million Suns into an area smaller than our solar system. Their confidence came from reading the motions of millions of fast-moving stars that swarm around the dense, central object.

Yet they've never seen it -- black holes by definition are invisible. And they don't really know how much space it takes up.

In fact, no one is even sure it is a black hole. It might instead be a dense concentration of exotic "dark" stars, for example.

But in the new study researchers claim to have seen the edge of darkness by spotting rapidly pulsing X-ray emissions thought to be created when superheated gas or other matter zooms beyond the point of no return, through an "event horizon" that marks the time-bending and space-warping outer limits of a black hole. "This is extremely exciting because it's the first time we have seen our own neighborhood supermassive black hole devour a chunk of material," said Frederick Baganoff of the Massachusetts Institute of Technology, who led the study. "It's as if the material there sent us a postcard before it fell in."

He said the material could be a hot gas or solid matter roughly the size of a comet. Or the pulse of emissions could possibly be the result of some intense magnetic flare, similar to solar flares seen on our Sun.

The X-ray emissions were found near a previously known strong source of radio emissions, known as Sagittarius A* (pronounced "Sagittarius A Star") at the center of the Milky Way. Astrophysicists have long suspected that the compact source of intense radio emissions is related to what's known as a supermassive black hole, the largest type of black hole and a variety suspected of anchoring many large galaxies.

The new observations, detailed here at a Chandra X-ray Observatory symposium, represent what may be the most direct evidence for the black hole's existence, several scientists said. And though they stopped short of calling it proof, researchers are hopeful that a final answer will come within a decade.

Galactic puppeteer

Most of our galaxy is relatively uncrowded. The nearest star to our Sun, for example, is 4.2 light-years away.

But roughly 10 million stars are known to orbit within a light year of the galaxy's center, dashing along at phenomenal speeds of up to 3.1 million mph (5 million kph). This concentration of stars, and the speed with which they orbit, is the main clue that something hugely massive is at the center of the Milky Way, acting like a galactic puppeteer by providing the tremendous gravity needed to tug at stars with invisible strings.

If it is in fact a black hole, then it must meet the technical definition laid out by Einstein's general theory of relativity: All its mass must be locked and hidden inside a sphere known as an event horizon, beyond which nothing -- not even light -- can escape.

Just before matter swirls into a black hole, scientists predict it will approach the speed of light and become superheated, giving off X-rays prior to entering the event horizon.

Generally, the suspected supermassive black hole at the center of the Milky Way is quiet as black holes go, rarely coughing up X-rays or other forms of light radiation. This puzzling feature has made it difficult to study and casts some doubt on whether Sagittarius A*, the radio source, really represents a black hole.

So the X-ray observations announced Wednesday eliminated some of that doubt and filled a data gap.

Intense flares

The new observations, made in October of 2000 by the Chandra space telescope orbiting Earth, span about two hours. Flares of X-rays were 45 times more powerful than typical emissions that had previously been spotted. And wild variations occurred on shorter time frames: The number of X-rays per second dropped by a factor of five over one 10-minute period and then jump again to high levels 10 minutes later.

"Such breathless variability is rarely seen in emissions from ponderous multi-million solar-mass objects," said Fulvio Melia, a researcher at the University of Arizona's Steward Observatory. This kind of activity is typically reserved for smaller objects, like neutron stars.

Melia was not involved in the study but has written an analysis of it for the Aug. 6 issue of the journal Nature, where the results will be published.

Because Chandra only sees the area near the black hole as a point in space, the X-ray peaks represent the entire output around the sphere of the event horizon. So if strong peaks of activity can build in just 10 minutes, then the entire event horizon that contributes to the total emissions must be no larger than the distance light can travel in 10 minutes -- roughly the distance from Earth to the Sun, Melia said.

This implies a size of the event horizon that is some 1,500 times smaller than previous research could determine -- much closer to the size predicted by the theory of general relativity. Though it may be as small as relativity predicts -- 5.6 million miles (9 million km) in diameter -- the new study can only say that it is no larger than 112 million miles (180 million km).

Could it be a cosmic trick?

In 1999, the same research group used Chandra to detect weak but steady X-rays near Sagittarius A*, data that has not been widely reported.

Combined, the two sets of observations strongly indicate that the radiation most likely comes directly from Sagittarius A* and not from some other object, such as a star that orbits close Sagittarius A* in some sort of "binary" configuration, Melia said.

But the observations are not entirely conclusive.

"Nature has been cruel to astronomers in other circumstances, and this probability, although small, is not zero," Melia said. He added that much more convincing evidence would come if astronomers could spot X-ray emissions and radio emissions that occur simultaneously from the same location.

Studies to look for such a convergence are underway, and an answer could come within a year, several researchers agreed.

Baganoff hopes to lead the team that makes that discovery. Will scientists then declare, once and for all, that there is a black hole at the center of the Milky Way Galaxy?

Not quite. Baganoff said researchers would have to actually image the event horizon, not just the emissions from it. If he and his colleagues spot a correlation between radio and X-ray flares in Sagittarius A* within the next year, then he said he would bet his career that the event horizon will be imaged within a decade.

But, he said, he wouldn't be quite ready to bet his life on it.

Contributing to the study were researchers from Penn State University, MIT, UCLA, Caltech, and Insititute of Space and Astronautical Science, Japan.

10 facts your mom didn't tell you about chandra

#10: Chandra flies 200 times higher than Hubble - more than 1/3 of the way to the moon!

#9: Chandra can observe X-rays from clouds of gas so vast that it takes light five million years to go from one side to the other!

#8: During maneuvers from one target to the next, Chandra slews more slowly than the minute hand on a clock.

#7: At 45 feet long, Chandra is the largest satellite the shuttle has ever launched!

#6: If Colorado were as smooth as Chandra's mirrors, Pikes Peak would be less than one inch tall!

#5: Chandra's resolving power is equivalent to the ability to read a stop sign at a distance of twelve miles.

#4:The electrical power required to operate the Chandra spacecraft and instruments is 2 kilowatts, about the same power as a hair dryer.

#3: The light from some of the quasars observed by Chandra will have been traveling through space for ten billion years.

#2: STS-93, the space mission that deployed Chandra, was the first NASA shuttle mission commanded
by a woman.

#1: Chandra can observe X-rays from particles up to the last second before they fall into a black hole!!!

WOW!!!

Supernova is 'smoking gun' in gamma-ray-burst whodunit

photo: Some scientists suspect that the x-ray afterglow following a gamma-ray burst is produced when a jet of high-energy particles shooting from a black hole (itself the remnant of an exploded star) slams into the expanding supernova shell. CXC / M. Weiss
Date: April 2, 2003

Every day there is a gamma-ray burst somewhere in the depths of space. Shining with the intensity of a million trillion suns only to fade away within seconds, these brilliant flashes are the most violent and enigmatic phenomena in the universe. But a team of astronomers using NASA's Chandra X-ray Observatory announced a breakthrough at last week's meeting of the High Energy Division of the American Astronomical Society in Quebec, Canada. The researchers explained that they tracked the afterglow of a gamma-ray burst for more than 21 hours and uncovered clear signatures characteristic of supernova explosions there.Comparable to a forensics investigation, a supernova explosion may be the proverbial smoking gun scientists have been looking for to understand the origins of gamma-ray bursts. According to the team leader, Nathaniel Butler from the Massachusetts Institute of Technology, "If a gamma-ray burst were a crime, then we now have strong circumstantial evidence that a supernova explosion was at the scene."



photo: Astronomers think gamma-ray bursts may be linked to black holes but aren't sure of the exact circumstances of their creation. One idea is that gamma-ray bursts are produced after a massive star explodes and leaves a black hole in its place. Another idea is that they're produced when two neutron stars collide to form a black hole. The appearance of a gamma-ray burst is unpredictable, but one appears about once per day. ESA / ECF

Designated GRB 020813, the gamma-ray burst was first detected by the High Energy Transient Explorer 2 (HETE-2) on August 13, 2002. Following the initial, intense burst of gamma rays, Chandra quickly swung into action to observe the x-ray afterglow. The grating spectrometer aboard Chandra revealed the presence of a supernova hidden beneath the powerful glow of the gamma-ray burst. An overabundance of heavy elements were clearly identified in the spectrum of GRB 020813, a distinct fingerprint pointing to the death throws of massive star."This is our first opportunity to see freshly minted material produced in supernova explosions" says University of Chicago co-investigator Donald Lamb. "Other times when we see supernova remnants, they have already been mixed a great deal with the interstellar medium."

Some believe that when a black hole forms as result of a supernova, jets of high-energy particles radiate outward into space, causing the initial, brief burst of powerful gamma rays. Within hours this hot jet of particles collides with the cloud of ejected remains of the dead star and produces an x-ray afterglow that is glimpsed by x-ray telescopes in Earth orbit.

Likened to a race between the tortoise and hare, the remnants ejected from the supernova explosion is slow in expanding at only a tenth the speed of light, while the x-rays that illuminate it are moving at the absolute speed of light. If the tortoise and the hare started at the same time, the slower supernova material could never get in front of the x-rays. This material, therefore is suggested to have been expelled some time before — possibly as much as 60 days — so that when the x-rays come out of the burst they can catch up to them.

Donald Lamb added, "This race between the tortoise of the ejected material and the hare of the x-ray afterglow is a strong piece of evidence that there is a two-stage event happening and supports the theory of a time delay between the supernova and the gamma-ray burst."

37-Year Search for Source of Mysterious 'X-ray Background' Ends

Date: 14 January 2000

Armed with the potent imaging power of the Chandra space telescope, a team of scientists claims to have answered a 37-year old question that has poked at astronomers since humanity’s first foray into high-energy astronomy: the mystery of the X-ray background radiation.

The Chandra telescope has given these scientists a glimpse at the source of the diffuse X-ray glow that seems to permeate the entire universe, said Richard Mushotzky, a researcher at NASA’s Goddard Space Flight Center.

That glow is produced by a "new class of objects" scattered throughout the universe that emit X-ray radiation, he said. The objects aren’t exactly unknown, but they were never before shown to be the sources of X-ray radiation, said Mushotzky, who leads a group of astronomers that used Chandra to study the puzzling universal X-ray glow.

He announced the discovery here Thursday at the meeting of the American Astronomical Society.X-ray astronomy must be done from space because Earth’s atmosphere blocks out X-ray radiation – the energy that comes from some of the hottest, most energetic objects in the universe.

The very first rocket flight that was capable of X-ray astronomy observed a diffuse glow that seemed to permeate the universe in every direction. The phenomenon was dubbed the X-ray background, and it has defied definitive explanation ever since.

Chandra’s ability to see objects 100 times fainter than previous X-ray instruments, though, means the telescope was, in some sense, built for the task, Mushotzky said.

The telescope allowed the astronomers to see the points that were emitting the peculiar brand of X-rays that seemed to come from everywhere and nowhere at all, and they discovered that these points were found throughout the universe -- perhaps 100 million of them spread over the entire sky, Mushotzky said.

"The heart of the background is made up of a rich assortment of X-ray sources which could not have been discovered by previous satellite missions," said Amy Barger, a University of Hawaii astronomer who worked to find optical counterparts to the X-ray sources.

Using ground-based telescopes, Barger chased down the source of many of the X-ray points and found that they could be classified into four categories.

Some of the X-rays come from galaxy clusters, and some from the energetic active galactic nuclei known as quasars. A third source seems to be bright galaxies, which look in most respects like any normal run-of-the-mill galaxy. The final category of sources simply can’t be seen at visible wavelengths, so Barger calls this class "optically-faint objects."

Most likely, the sources in all these cases are super-massive black holes, either in the centers of galaxies or galaxy clusters, or hidden from view by surrounding clouds of dust, Barger said.

She reasons that the optically faint sources might be black holes so shrouded by gunk that visible light is blocked out while X-rays escape to scatter throughout the universe.

Astronomers who worked on the problem are relieved, and are hailing the discovery as something big. Still, the answer is not a complete surprise, for many scientists have suggested that the background must be created by a diverse array of objects throughout the universe. Still, until now it has never been proved, Mushotzky said.

For years the uncertainty of the X-ray background's source has been an irritant to cosmologists, said Virginia Trimble, of the University of California at Irvine.

Trimble, who is not affiliated with the team that announced the discovery said that knowing the sources of the X-ray radiation should help cosmologists develop better understandings about the overall shape and structure of the universe. One of the great questions of the day, she said, is why is the universe lumpy, and not smooth and homogeneous throughout. The new discovery could help answer those questions, Trimble said.

"The X-ray background has subtle fluctuations in it. You could use those to trace large-scale structure if only you knew what was making that X-ray background. We now know what is making that X-ray background," she said.

Extended X-Ray Jet in Nearby Galaxy Reveals Energy Source

photo: At a distance of 11 million light years, Centaurus A or NGC 5128, is the nearest example of a type of galaxy called an active galaxy. It is a large elliptically shaped galaxy that shows evidence of repeated explosions, probably from a supermassive black hole in the center of the galaxy. Radio and X-ray images of the galaxy show a jet of high-energy particles blasting out from the center. Because of its unusual nature and proximity, it is one of the most extensively studied galaxies in the southern hemisphere.(X-ray image)

Date:October 25, 1999

NASA's Chandra X-ray Observatory has made an extraordinary image of Centaurus A, a nearby galaxy noted for its explosive activity. The image shows X-ray jets erupting from the center of the galaxy over a distance of 25,000 light years. Also detected are a group of X-ray sources clustered around the nucleus, which is believed to harbor a supermassive black hole. The X-ray jets and the cluster of sources may be a byproduct of a titanic collision between galaxies several hundred million years ago.

"This image is great," said Dr. Ethan Schreier of the Space Telescope Science Institute, "For twenty years we have been trying to understand what produced the X rays seen in the Centaurus A jet. Now we at last know that the X-ray emission is produced by extremely high-energy electrons spiraling around a magnetic field." Schreier explained that the length and shape of the X-ray jet pinned down the source of the radiation. The entire length of the X-ray jet is comparable to the diameter of the Milky Way Galaxy.

Other features of the image excite scientists. "Besides the jets, one of the first things I noticed about the image was the new population of sources in the center of the galaxy," said Dr. Christine Jones from the Harvard-Smithsonian Center for Astrophysics . "They are grouped in a sphere around the nucleus, which must be telling us something very fundamental about how the galaxy, and the supermassive black hole in the center, were formed."

Astronomers have accumulated evidence with optical and infrared telescopes that Centaurus A collided with a small spiral galaxy several hundred million years ago. This collision is believed to have triggered a burst of star formation and supplied gas to fuel the activity of the central black hole.

more -

According to Dr. Giuseppina Fabbiano, of Harvard-Smithsonian, "The Chandra image is like having a whole new laboratory to work in. Now we can see the main jet, the counter jet, and the extension of the jets beyond the galaxy. It is gorgeous in the detail it reveals," she said.Dr. Allyn Tennnant of NASA's Marshall Space Flight Center agreed. "It's incredible, being able to see all that structure in the jet," he said. "We have one fine X-ray telescope."

Indeed at a distance of eleven million light years from Earth, Centaurus A has long been a favorite target of astronomers because it is the nearest example of a class of galaxies called active galaxies. Active galaxies are noted for their explosive activity, which is presumed to be due to a supermassive black hole in their center. The energy output due to the huge central black hole can in many cases affect the appearance of the entire galaxy.

The Chandra X-ray image of Cen A, made with the High Resolution Camera, shows a bright source in the nucleus of the galaxy at the location of the suspected supermassive black hole. The bright jet extending out from the nucleus to the upper left is due to explosive activity around the black hole which ejects matter at high speeds from the vicinity of the black hole. A "counter jet" extending to the lower right can also be seen. This jet is probably pointing away from us, which accounts for its faint appearance.

One of the most intriguing features of supermassive black holes is that they do not suck up all the matter that falls within their sphere of influence. Some of the matter falls inexorably toward the black hole, and some explodes away from the black hole in high-energy jets that move at near the speed of light. The presence of bright X-ray jets in the Chandra image means that electric fields are continually accelerating electrons to extremely high energies over enormous distances. Exactly how this happens is a major puzzle that Chandra may help to solve.

Shocking Detail of Superstar's Activity Revealed

photo: Eta Carinae is the most luminous star known in our galaxy. It radiates energy at a rate that is 5 million times that of the Sun. Observations indicate that Eta Carinae is an unstable star that is rapidly boiling matter off its surface. Some astronomers think that it could explode as a supernova any time! At a distance of 7,000 light years from Earth, this gigantic explosion would pose no threat to life but it would be quite a show.

Date:October 8, 1999

NASA's Chandra X-ray Observatory has imaged Eta Carinae and revealed a hot inner core around this mysterious superstar. The new X-ray observation shows three distinct structures: an outer, horseshoe shaped ring about two light years in diameter, a hot inner core about 3 light months in diameter, and a hot central source less than a light month in diameter which may contain the superstar.

All three structures are thought to represent shock waves produced by matter rushing away from the superstar at supersonic speeds. The temperature of the shock-heated gas ranges from 60 million degrees Celsius in the central regions to 3 million degrees Celsius on the outer structure.

An earlier image of Eta Carinae by the Hubble Space Telescope revealed two spectacular bubbles of gas expanding in opposite directions away from a central bright region at speeds in excess of a million miles per hour. The inner region visible in the Chandra image has never been resolved before, and appears to be associated with a central disk of high velocity gas rushing out at much higher speeds perpendicular to the bipolar optical nebula.

"It is not what I expected," said Dr. Fred Seward of the Harvard-Smithsonian Center for Astrophysics. "I expected to see a strong point source with a little diffuse emission cloud around it. Instead, we see just the opposite– a bright cloud of diffuse emission, and much less radiation from the center."

"The Chandra image contains some puzzles for existing ideas of how a star can produce such hot and intense X-rays," agreed Prof. Kris Davidson of the University of Minnesota. "In the most popular theory, X-rays are made by colliding gas streams from two stars so close together that they'd look like a point source to us. But what happens to gas streams that escape to farther distances? The extended hot stuff in the middle of the new image gives demanding new conditions for any theory to meet."

Eta Carinae is one of the most enigmatic and intriguing objects in our galaxy. Between 1837 and 1856 it increased dramatically in brightness to become the brightest star in the sky except for Sirius, even though it is 7,500 light years away, more than eighty times the distance to Sirius. This "Great Eruption," as it is called, had an energy comparable to a supernova, yet did not destroy the star, which faded to become a dim star, invisible to the naked eye. Since 1940, Eta Carinae has begun to brighten again, becoming visible to the naked eye.

Modern day observations of Eta Carinae have shown it to be the most luminous object known in our galaxy. It radiates at the rate of several million times that of the Sun. Most of the radiation is at infrared wavelengths, from dust in the bipolar nebula. Astronomers still do not know what lies at the heart of Eta Carinae. Most believe that it is powered by an extremely massive star that may be a hundred times as massive as the Sun. Such stars produce intense amounts of radiation that cause violent instabilities before they explode as a supernova.

The Chandra X-ray image gives a glimpse deep into the nebula where the fastest material being thrown off by Eta Carinae is found. The outer ring provides evidence of another large explosion that occurred over a thousand years ago. Further Chandra observations of Eta Carinae are planned for the near future and should give astronomers deeper insight into this cryptic colossus.

Chandra Discovers X-Ray Ring Around Cosmic Powerhouse in Crab Nebula

photo:The Crab Nebula is the remnant of a supernova explosion that was seen on Earth in 1054 AD. It is 6000 light years from Earth. At the center of the bright nebula is a rapidly spinning neutron star, or pulsar that emits pulses of radiation 30 times a second.

After barely two months in space, NASA's Chandra X-ray Observatory has taken a stunning image of the Crab Nebula, the spectacular remains of a stellar explosion, and has revealed something never seen before: a brilliant ring around the nebula's heart.

Combined with observations from the Hubble Space Telescope, the image provides important clues to the puzzle of how the cosmic "generator," a pulsing neutron star, energizes the nebula, which still glows brightly almost 1,000 years after the explosion.

"The inner ring is unique," said Professor Jeff Hester of Arizona State University, Tempe, AZ. "It has never been seen before, and it should tell us a lot about how the energy from the pulsar gets into the nebula. It's like finding the transmission lines between the power plant and the light bulb."

Professor Mal Ruderman of Columbia University, New York, NY, agreed. "The X-rays Chandra sees are the best tracer of where the energy is. With images such as these, we can directly diagnose what is going on."

What is going on, according to Dr. Martin Weisskopf, Chandra Project Scientist from NASA's Marshall Space Flight Center, Huntsville, AL, is awesome. "The Crab pulsar is accelerating particles up to the speed of light and flinging them out into interstellar space at an incredible rate."

The image shows tilted rings or waves of high-energy particles that appear to have been flung outward over the distance of a light year from the central star, and high-energy jets of particles blasting away from the neutron star in a direction perpendicular to the spiral.

Hubble Space Telescope images have shown moving knots and wisps around the neutron star, and previous X-ray images have shown the outer parts of the jet and hinted at the ring structure. With Chandra's exceptional resolution, the jet can be traced all the way in to the neutron star, and the ring pattern clearly appears. The image was made with Chandra's Advanced CCD Imaging Spectrometer and High Energy Transmission Grating.

The Crab Nebula, easily the most intensively studied object beyond our solar system, is the remnant of a star that was observed to explode in 1054 A.D. Chinese astronomers in that year reported a "guest star" that appeared suddenly and remained visible for weeks, even during daytime. From gamma-ray telescopes to radio telescopes, the Crab has been observed using virtually every astronomical instrument that could see that part of the sky.

Unraveling the mysteries of the Crab has proven to be the door to insight after insight into the workings of the universe. The Crab convincingly tied the origin of enigmatic "pulsars" to the stellar cataclysms known as supernovas. Observations of the expanding cloud of filaments in the Crab were instrumental in confirming the cosmic origin of the chemical elements from which planets (and people) are made.

The nebula is located 6,000 light years from Earth in the constellation Taurus. The Crab pulsar, which was discovered by radio astronomers in 1968, is a neutron star rotating 30 times per second. Neutron stars are formed in the seconds before a supernova explosion when gravity crushes the central core of the star to densities 50 trillion times that of lead and a diameter of only 12 miles.

Another consequence of the dramatic collapse is that neutron stars are rapidly rotating and highly magnetized. Like a gigantic cosmic generator, the rotating magnet generates 10 quadrillion volts of electricity, 30 million times that of a typical lightning bolt.

"It is an incredibly efficient generator," Ruderman explained. "More than ninety-five percent efficient. There's nothing like it on Earth."

Chandra Images Provide New Vision of Cosmic Explosions

photo:PSR 0540-69 is a neutron star, or pulsar, that is rotating very rapidly, making a complete rotation every one-twentieth of a second. It is similar in many ways to the famous Crab Nebula pulsar. Both objects are spinning rapidly, are about 1,000 years old and are surrounded by a large cloud of gas and high-energy particles. The surrounding cloud in both cases is powered by the conversion of rotational energy of the neutron star into high energy particles through the combined action of rapid rotation and a strong magnetic field. PSR 0540-69 is 160,000 light years away in the Large Magellanic Cloud, one the Milky Way's small satellite galaxies.



photo: The identification of G21.5-0.9 as the remnant of a supernova explosion is based on indirect evidence from radio and X-ray observations. At both radio and X-ray wavelengths, it appears as round patch in the sky. Detailed observations with radio telescopes confirm that the radio waves are produced by high energy electrons spiraling around magnetic field lines (synchrotron radiation). The X-rays are probably produced by the same process, but the electrons involved have energies many thousands times higher than those that produce the radio waves. The favored theory is that the high-energy electrons responsible for both the radio and X-ray emission are produced by a rapidly rotating, highly magnetized neutron star left behind when a massive star exploded some 40,000 years ago.



photo:E0102-72 is a supernova remnant in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. This galaxy is 190,000 light years from Earth. E0102 -72, which is approximately a thousand years old, is believed to have resulted from the explosion of a massive star. Stretching across forty light years of space, the multi-million degree source resembles a flaming cosmic wheel.

Images from NASA's Chandra X-ray Observatory released today reveal previously unobserved features in the remnants of three different supernova explosions. Two of the remnants G21.5-0.9 and PSR 0540-69 show dramatic details of the prodigious production of energetic particles by a rapidly rotating, highly magnetized neutron star, as well as the enormous shell structures produced by the explosions. The image of the third remnant, E0102-72, reveals puzzling spoke-like structures in its interior.

G21.5-0.9, in the constellation of Scutum, is about 16,000 light years (1 light year = 6 trillion miles) from Earth. Chandra's image shows a bright nebula surrounded by a much larger diffuse cloud. Inside the inner nebula is a bright central source that is thought to be a rapidly rotating highly magnetized neutron star. A rotating neutron star acts like a powerful generator, creating intense electric voltages that accelerate electrons to speeds close to the speed of light. The total output of this generator is greater than a thousand suns. The fluffy appearance of the central nebula is thought to be due to magnetic field lines which constrain the motions of the high-energy electrons.

"It's a remarkable image," said Dr. Patrick Slane of the Harvard-Smithsonian Center for Astrophysics. "Neither the inner core nor the outer shell has ever been seen before."

"It is as though we have a set of Russian dolls, with structures embedded within structures," said Professor Gordon Garmire of Penn State University, and principal investigator of the Advanced CCD Imaging Spectrometer, the X-ray camera that was used to make two of the images.

NASA's project scientist, Dr. Martin Weisskopf of the Marshall Space Flight Center said, "Chandra's capability to provide surprises and insights continues." The existence of a rotating neutron star, or pulsar, in the center of G21.5-0.9 is inferred from the appearance of the nebula and the energy distribution of X-rays and radio waves from the nebula. This distribution, called non-thermal radiation is characteristic of radiation produced by high-energy electrons in a magnetic field.

A previously known pulsar is observed directly in the Chandra image of PSR 0540-69. This pulsar, located in a satellite galaxy to the Milky Way that is 180,000 light years distant, emits pulses of radio, optical, and X radiation at a rate of 50 per sec. These pulses which come from a neutron star rotating at this incredible rate, comprise only a few percent of the total energy output of the neutron star powerhouse.

"The Chandra image gives us a much better idea of how this energy source works," said Dr. Stephen Murray, principal investigator for the High Resolution Camera, the X-ray camera used to make PSR 0540-69 image. "You can see X-ray jets blasting out from the pulsar in both directions."

The third Chandra supernova image is E0102-72. Located in the Small Magellanic Cloud, another satellite galaxy of the Milky Way, E0102-72 is 190,000 light years from Earth. This object, like G21.5-0.9 and PSR 0540-69, is believed to have resulted from the explosion of a massive star several thousand years ago. Stretching across 40 light years of space, the multi-million degree source resembles a flaming cosmic wheel.

"Chandra's gallery of supernova remnants is giving us a lot to think about," said Dr. Fred Seward, of Harvard-Smithsonian, who with his colleagues discovered E0102-72 and PSR 0540-69 with the Einstein Observatory over a decade ago. "We're seeing many things we thought should be there, and many others that we never expected. It's great!"

Date:September 20, 1999

Distant Supernova Remnant Imaged by Chandra's High Resolution Camera

photo: N132D is the remnant of an exploded star in the Large Magellanic Cloud. The Chandra image shows a highly structured remnant, or shell, of 10-million-degree gas that is 80 light years across. The remnant is thought to be about 3,000 years old. The Large Magellanic Cloud, a companion galaxy to the Milky Way, is 160,000 light years from Earth.(X-ray Image)(Credit: NASA/CXC/SAO)

Date:September 10, 1999

Chandra's first image of a quasar

photo:PKS 0637-752 is so distant that we see it as it was 6 billion years ago. It is a luminous quasar that radiates with the power of 10 trillion suns from a region smaller than our solar system. The source of this prodigious energy is believed to be a supermassive black hole.(X-ray image)

Date:August 26, 1999

NASA Unveils First Images From Chandra X-Ray Observatory

photo: (Cassiopeia A:First Light)(X-ray Image)
Cas A is the remnant of a star that exploded about 300 years ago. The X-ray image shows an expanding shell of hot gas produced by the explosion. This gaseous shell is about 10 light years in diameter, and has a temperature of about 50 million degrees.

Date:August 26, 1999

Extraordinary first images from NASA's Chandra X-ray Observatory trace the aftermath of a gigantic stellar explosion in such stunning detail that scientists can see evidence of what may be a neutron star or black hole near the center. Another image shows a powerful X-ray jet blasting 200,000 light years into intergalactic space from a distant quasar.

Released today, both images confirm that NASA's newest Great Observatory is in excellent health and its instruments and optics are performing up to expectations. Chandra, the world's largest and most sensitive X-ray telescope, is still in its orbital check-out and calibration phase.

"When I saw the first image, I knew that the dream had been realized," said Dr. Martin Weisskopf, Chandra Project Scientist, NASA's Marshall Space Flight Center, Huntsville, AL. "This observatory is ready to take its place in the history of spectacular scientific achievements."

"We were astounded by these images," said Harvey Tananbaum, Director of the Smithsonian Astrophysical Observatory's Chandra X- ray Center, Cambridge, MA. "We see the collision of the debris from the exploded star with the matter around it, we see shock waves rushing into interstellar space at millions of miles per hour, and, as a real bonus, we see for the first time a tantalizing bright point near the center of the remnant that could possibly be a collapsed star associated with the outburst." After the telescope's sunshade door was opened last week, one of the first images taken was of the 320-year-old supernova remnant Cassiopeia A, which astronomers believe was produced by the explosion of a massive star. Material blasted into space from the explosion crashed into surrounding material at 10 million miles per hour. This collision caused violent shock waves, like massive sonic booms, creating a vast 50-million degree bubble of X-ray emitting gas.

Heavy elements in the hot gas produce X-rays of specific energies. Chandra's ability to precisely measure these X-rays tells how much of each element is present. With this information, astronomers can investigate how the elements necessary for life are created and spread throughout the galaxy by exploding stars. "Chandra will help to confirm one of the most fascinating theories of modern science -- that we came from the stars," said Professor Robert Kirshner of Harvard University. "Its ability to make X-ray images of comparable quality to optical images will have an impact on virtually every area of astronomy."

Chandra also imaged a distant and very luminous quasar -- a single star-like object -- sporting a powerful X-ray jet blasting into space. The quasar radiates with the power of 10 trillion suns, energy which scientists believe comes from a supermassive black hole at its center. Chandra's image, combined with radio telescope observations, should provide insight into the process by which supermassive black holes can produce such cosmic jets.

"Chandra has allowed NASA to seize the opportunity to put the U.S. back in the lead of observational X-ray astronomy," said Dr. Edward Weiler, Associate Administrator of Space Science, NASA Headquarters, Washington, DC. "History teaches us that whenever you develop a telescope 10 times better than what came before, you will revolutionize astronomy. Chandra is poised to do just that."

The Chandra X-ray observatory was named in honor of the late Nobel laureate Subrahmanyan Chandrasekhar. NASA's Marshall Space Flight Center manages the Chandra program. TRW, Inc., Redondo Beach, CA, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, MA.