Chandra finds smallest supermassive black hole yet

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Researchers using the Chandra X-ray observatory have found what they think is the smallest supermassive black hole yet.

Astronomers from George Mason University in Virginia have found what they think is the lowest mass supermassive black hole at the center of NGC4178 using data from the Chandra X-ray observatory, Spitzer telescope and Very Large Array radio telescopes.

[quote]In this image, the purple X-ray spectrum image shows a large x-ray source at the center of NGC4178, thought to be a supermassive black hole. Image Courtesy JPL/NASA[/quote]

It is generally accepted that at the center of each galaxy is a supermassive black hole – a very large black hole with a mass hundreds of thousands or even millions of times the mass of our sun. The mass of these black holes creates a noticeable bulge at the center of the galaxy if you were to look at the galaxy’s disk edge-on, as stars orbit it in a roughly spherical cloud.

NGC4178 is an unusual galaxy in this regard as it doesn’t have a central bulge. A known relationship between the mass of a black hole and the amount of X-rays and radio waves it generates was used to estimate the mass of the black hole, placing it at the low end of the scale for supermassive black hole size – less than 200,000 times the mass of our Sun.

Besides NGC 4178, four other galaxies without bulges are currently thought to contain supermassive black holes. Of these four black holes, two have masses that may be close to that of the black hole in NGC 4178. Observations of an X-ray source discovered by Chandra in the center of the galaxy NGC 4561 indicate that the mass of this black hole is greater than 20,000 times the mass of the sun, particularly low for supermassive black holes.

X ray emission from black holes is normally produced by material within the accretion disk. As the black hole draws material towards it, frictional forces between the material particles causes those particles to heat to vast temperatures. At this point the temperature of the material is high enough to strip electrons from the atoms of the material, forming a state of matter called plasma that emits high energy x-rays. One explanation for the exceedingly low mass of the supermassive black hole at the center of NGC 4561 is that the black hole is drawing in material at an exceptionally slow rate, causing relatively little heating in its accretion disk.

The researchers, led by Nathan Seacrest from George Mason University published their study in the July 1st 2012 issue of The Astrophysical Journal.

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