XMM source variations in M31
Credit: S. Trudolyubov and ESA

X-ray Flashers in M31

The Milky Way's neighbor, the Andromeda Galaxy (M31) is a large spiral galaxy similar to the Milky Way. X-ray astronomers like to study M31 since they can see the entire galaxy at once. This lets them determine the population of black holes and other compact objects and to see how these objects are distributed through the galaxy. Since all the objects in M31 are at nearly the same distance from us, this enables astronomers to get an accurate measure of the object's luminosity. X-ray astronomers also have an advantage over optical astronomers, since the number of compact objects in M31 (or in any galaxy for that matter) is much less than the number of visible stars, so source confusion is not much of an issue. Also, since most compact X-ray sources vary, detection of variability is a big help in distinguishing X-ray bright compact objects from X-ray bright extended objects (like young supernova remnants). The most sensitive X-ray pictures of M31 have recently been obtained by the EPIC camera on the XMM-Newton observatory. The XMM-Newton images of the center of M31, shown above, were obtained roughly 6 months apart and show dozens of X-ray sources (including a supermassive black hole near the very center of M31). The source within the green circle is an usual X-ray transient in which the energy of the emitted X-rays is very low, and the source within the yellow circle is newly discovered X-ray Nova designated XMMU J004234.1+411808. Many of these sources are variable; some of the more obvious variables are indicated by the red arrows. You can see an impressive display of source variability by blinking the images.

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Each week the HEASARC brings you new, exciting and beautiful images from X-ray and Gamma ray astronomy. Check back each week and be sure to check out the HEAPOW archive!

Page Author: Dr. Michael F. Corcoran
Last modified July 3, 2001