This X-ray image shows the central portion of the Andromeda Galaxy. The blue dot in the center of the image is a "cool" million degree X-ray source where a supermassive black hole with the mass of 30 million suns is located.The X-rays are produced by matter funneling toward the black hole.
Note: see update file for corrected location of black hole.
In its first look at the Andromeda Galaxy (M31), NASA's Chandra X-ray Observatory has found that the gas funneling into a supermassive black hole in the heart of this galaxy is a "cool" million degrees Celsius. This unexpected result adds one more quirk to the strange behavior previously observed at the center of M31.
Chandra took its first X-ray picture of the Andromeda Galaxy with the Advanced CCD Imaging Spectrometer on October 13, 1999. More than100 individual X-ray sources were seen. One of these sources was at the previously determined position of the central supermassive black hole, which has the mass of 30 million suns. With many X-ray emitting stars in the center of M31 there was a slight chance that one of them might be at this position just by coincidence. The low temperature of the suspected central source, as compared to the other sources, gave the team the clue they needed.
"When we found that what we suspected was the central object was also anomalously cool, we KNEW we had it one coincidence might be believable, but two was too much to ignore!" said Michael Garcia (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.).
While the gas falling into the central black hole is cool, it is only cool by comparison to the 100 other X-ray sources in the Andromeda Galaxy. To be detected by an X-ray telescope, the gas must have a temperature of more than a million degrees Celsius. The typical X-ray star in the Andromeda Galaxy has a temperature of several tens of millions of degrees. In contrast, the temperature of the supermassive black hole source is a few million degrees Celsius.
The Andromeda Galaxy is our nearest neighbor spiral galaxy at a distance of two million light years. It is similar to our own Milky Way in size, shape, and also contains a supermassive black hole at the center.
"The Chandra observation is telling us that an entirely different flow pattern is operating around the Andromeda black hole," said Dr. Eliot Quataert, of the Institute for Advanced Study, Princeton, N.J. "This will require a different class of models than usually considered."
Another intriguing feature of this observation is the detection of a diffuse glow that extends for a thousand light years around the central region. It is not known if this is due to many individual sources, or to a hot wind expanding out from the center.
"This is just a first, quick look at our nearest Milky Way analog," Murray emphasized. "I expect that our future pictures will lead to more exciting discoveries in the Andromeda Galaxy."