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Peeking at a galaxy far, far away NASA 'reads' stars with X-ray telescope Saturday, January 15, 2000 By Byron Spice, Science Editor, Post-Gazette
Star births and deaths proceed with the relative calm of campfire embers in the Milky Way, but NASA's new Chandra X-ray Observatory shows that these events are more akin to exploding fireworks in galaxies known to have a high rate of star formation.
In one such "starburst" galaxy, called M82, Chandra has uncovered at least 20 unusual binary systems, each thought to be a massive star in a death dance with a black hole. It also has found a cloud of interstellar gas heated to 100 million degrees, probably by a rapid succession of exploding stars.
One thing that Chandra has not found in M82, the starburst galaxy closest to Earth, is a medium-size black hole. Astronomers at Carnegie Mellon University and in Japan last year independently found X-ray evidence in M82 of this new class of black holes. But CMU astrophysicist Richard Griffiths said a closer look with Chandra's sharp eye failed to confirm its existence.
"We were surprised and a bit disappointed by that," Griffiths said. "That's the nature of science."
But Griffiths and other astronomers are excited by what Chandra has revealed since its launch last summer, particularly in what is being learned about the nature of star formation in the early universe. Some of the first scientific findings from the orbiting X-ray telescope were presented yesterday at the American Astronomical Society meeting in Atlanta.
In addition to the M82 study, the Chandra findings released yesterday include a quasar-like X-ray source associated with the supermassive black hole at the center of the Milky Way, and nearly a thousand faint X-ray-emitting stars in the sword of Orion -- the richest field of X-ray sources ever seen.
"It's the first time we've seen so many sources," said Gordon Garmire, a Penn State University astronomer who leads the group that uses Chandra's Advanced CCD Imaging Spectrometer, an X-ray camera that for the first time matches the fine detail that the Hubble Space Telescope provides for objects emitting visible light. "It opens up whole new fields of study."
M82 has long been known to be an unusually active galaxy. In the 1960s, it was called "the exploding galaxy." But Chandra has revealed some surprises, including those 20 binary systems thought to include black holes.
"We've never seen these before," said Griffiths, who with Garmire is part of the team of astronomers analyzing the M82 data. More study will be necessary to confirm exactly what they are, but their brightness suggests they are massive stars orbiting black holes. The black hole, a superdense object with gravity so intense that nothing can escape, would be siphoning off matter from its massive companion; X-rays would be emitted as this material is heated when it draws near the black hole.
A cloud of interstellar gas can be seen in M82 that measures 100 million degrees, about 100 times hotter than interstellar gas found in the Milky Way. Stars explode every few years in M82, Griffiths noted, so the gas may be heated by colliding shock waves from this rapid succession of supernovae.
Chandra has not found the medium-size black hole, with a mass of between 100 and 10,000 suns, that Griffiths and Andrew Ptak last year suspected was within M82. "The source is 10 times fainter than it was," Griffiths said. "It shouldn't have faded that much." It might be a very massive binary star instead.
But Garmire said it's too soon to dismiss the possibility of a medium-size black hole. Even the diminished object remains massive -- perhaps 10 to 100 times the sun.
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