Baby Black Holes Lurking Near Galactic Centre
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.
At Keio University in Japan, a research team led by Associate Professor Tomoharu Oka, has made a remarkable discovery about one of the Universe’s biggest mysteries.
They found intermediate-mass black hole (IMBH) candidates at the center of the Milky Way Galaxy. Tucked away in the direction of the constellation of Sagittarius and near the galactic center, these 30,000 light year distant “embryos” could be the forerunners of massive black holes.
Through the use of radio telescopes, the research team lead by Dr. Oka has identified four “warm, dense (more than 50 degrees Kelvin, more than 10,000 hydrogen molecules per cubic centimeter)” masses of molecular gas – three of which have been expanding.
Oka, the research team leader, said, “The results are astonishing.” The “warm, dense” molecular gas in that area is concentrated in four clumps (Sgr A, L=+1.3°, L=–0.4°, L=–1.2°). Moreover, it turns out that these four gas clumps are all moving at a very fast speed of more than 100 km/s. Sgr A, one of the four gas clumps, contains “Sagittarius A*,” the nucleus of the Milky Way Galaxy. Oka added, “The remaining three gas clumps are objects we discovered for the very first time. It is thought that ‘Sagittarius A*’ is the location of a supermassive black hole that is approximately 4 million times the mass of the sun. It can be inferred that the gas clump ‘Sgr A’ has a disk-shaped structure with radius of 25 light-years and revolves around the supermassive black hole at a very fast speed.”
Spatial distribution of “warm, dense gas” (above) at the center of the Milky Way Galaxy and its velocity distribution (below). Distribution of the whole molecular gas is indicated by pale white. It can be understood that “warm, dense gas” is localized in four areas, and all the gas is moving at a fast speed. (Credit: Keio University)
What could be responsible for this fast evolution? The new research indicates a several supernova events located in the gas masses may be responsible for the expansion. According to their data, the largest of these packed the power of 200 “normal” supernovae events. However, the age of the gas masses is estimated to be approximately 60,000 years – inferring a huge star cluster may be embedded within them. The mass of the cluster is estimated to be 100,000 times that of the Sun and roughly the size of the largest known star clusters in the Milky Way. Even as large as it could be, it hasn’t been discovered until now.
“The solar system is located at the edge of the Milky Way Galaxy’s disk, and is about 30,000 light-years away from the center of the Milky Way Galaxy. The huge amount of gas and dust lying between the solar system and the center of the Milky Way Galaxy prevent not only visible light, but also infrared light, from reaching the earth. Moreover, innumerable stars in the bulge and disc of the Milky Way Galaxy lie in the line of sight. Therefore, no matter how large the star cluster is, it is very difficult to directly see the star cluster at the center of the Milky Way Galaxy,” Oka explained. “Huge star clusters at the center of the Milky Way Galaxy have an important role related to formation and growth of the Milky Way Galaxy’s nucleus.”
While it is widely accepted that all galaxies have a black hole at their center, new theories point towards intermediate and stellar size black holes as being commonplace throughout galactic structure, forming in huge star clusters. It stands to reason that IMBHs which are “born” near the center of the Milky Way will eventually expand into a supermassive black hole at the nucleus.
“We would like to observe IMBHs in the star cluster. Actually, our observation data has already indicated traces of IMBHs,” Oka said. One of the newly discovered gas masses, “L=–0.4°,” contains two small gas clumps moving at a very fast speeds. If it is confirmed that these small gas clumps are rotating, it can be inferred that there are “invisible huge masses” at the center of the gas clumps. These “invisible huge masses” are likely to be IMBHs hidden in the center of the star cluster. Professor Oka expects developments in future research, saying, “In order to confirm the existence of IMBHs, we are planning to conduct further observations. The new discovery is an important step toward unraveling the formation and growth mechanism of the supermassive black hole at the Milky Way Galaxy’s nucleus, which is a top-priority issue in galactic physics.”
Original Story Source: National Astronomical Observatory of Japan News Release.
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