Seeds of massive black holes found at center of the Milky Way

A research team has discovered masses thought to be “seeds” that form and grow massive black holes at the center of the Milky Way Galaxy, about 30,000 light-years from our solar system in the direction of Sagittarius.

Spatial distribution of molecular gas at the center of the Milky Way Galaxy, which is observed with wavelengths of 0.87 mm emitted from carbon monoxide molecules. The black cross mark indicates the position of “Sagittarius A*,” the nucleus of the Milky Way Galaxy. (Credit: Keio University)

Using radio telescopes, the Keio University team, led by Associate Professor Tomoharu Oka, has found four “warm, dense (more than 50 degrees Kelvin, more than 10,000 hydrogen molecules per cubic centimeter)” masses of molecular gas at the center of the Milky Way Galaxy.

A conceptual image of the newly discovered “large star cluster buried in dust.” It is considered that IMBHs are formed at the center of the cluster. Image credit: Keio University

Three of those masses of molecular gas have been expanding. This research suggests that supernova explosions caused the expansion. It is estimated that the largest explosion that occurred in the masses of molecular gas is equivalent to 200 supernova explosions. On the other hand, the age of the gas masses is approximately 60,000 years old. Therefore, it can be inferred that a huge star cluster is buried in one of the gas masses. The mass of the cluster (more than 100,000 times the mass of the sun) is comparable to the largest star cluster found in the Milky Way Galaxy.

These masses are referred to as intermediate-mass black hole (IMBH) candidates. It is thought that IMBHs are formed within such huge star clusters. Eventually, IMBHs born near the center of the Milky Way Galaxy form/expand into a supermassive black hole at the nucleus of the galaxy.

These research findings have been published in Astrophysical Journal Supplement Series, vol.201, pp14-25, a professional American astrophysics journal.
Read more about it from the National Observatory of Japan

July 23, 2012

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