A Look Back in Time Reveals a Vicious Cycle
It took only 40 hours for NASA's Chandra X-ray Observatory to focus on a hundred million years' worth of galactic violence.
Long-exposure images taken by Chandra have been combined with observations from radio telescopes, providing an extraordinarily detailed glimpse into the violent history of galaxy M87. The observations, captured by Chandra's Advanced CCD Imaging Spectrometer, are like a window to the past.
Image to left: Two Chandra X-ray Observatory views of the giant elliptical galaxy M87 were combined to make this long-exposure image. A central jet is surrounded by nearby bright arcs and dark cavities. Much further out, faint rings and two spectacular plumes are visible.
Credit: NASA/Chandra X-ray Center
Located in the middle of the Virgo galaxy cluster, M87 is 50 million light years from Earth. For comparison, consider that our own Milky Way galaxy is only about 100,000 light-years wide, and the neighboring Andromeda Galaxy is merely 2.3 million light-years away.
In the eye-catching picture that emerges, magnetized rings, buoyant bubbles, lengthy plumes and a jet of high-energy particles are seen blasting away from the supermassive black hole at the galaxy's core. Astronomers believe these features, seen now in unprecedented focus, reveal that the black hole has subjected its surrounding atmosphere to a cycle of repeated outbursts over the course of millions of years.
M87's center is dominated by X-rays from its jet, which points almost straight toward the camera. Two barely-visible circular rings are most likely sound waves produced by explosions about 10 million and 14 million years ago, and a very faint arc beyond the farthest ring is even older -- about 100 million years! The rings might also be shock waves, surrounding the jet and expanding outward.
Spectacular, curved X-ray plumes stretch dramatically from the upper left to the lower right, proving that a central black hole can affect the farthest reaches of a galaxy. These plumes, and bright arcs surrounding dark cavities of reduced X-rays, are believed to be gas swept up by buoyant bubbles born during an ancient outburst.
Image to right: X-ray and radio observations of galaxy M87 were combined to create this composite image.
Credit: X-ray: NASA/Chandra X-ray Center; Radio: National Radio Astronomy Observatory/Very Large Array
Astronomers are finding more and more evidence that these vicious cycles are frequent in giant galaxies with supermassive black holes. Why would a black hole periodically let loose with such forceful blasts? Perhaps when gas around the black hole cools and flows inward, it produces a powerful outburst that prevents anything more from falling in. At that point, the cycle might begin again. The cause might also be a single dramatic event, like a collision with a smaller galaxy and a merging of two black holes.
Only time -- and further research -- will tell if these cycles truly are as common as they are beginning to appear. Undoubtedly, scientists will continue to benefit from Chandra's unblinking view into the past.
For more information, visit:
http://chandra.harvard.edu/photo/2004/m87/
Anna Heiney, KSC Staff Writer
Chandra X-ray Center and NASA's John F. Kennedy Space Center
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