Astronomers from Moscow State University have discovered a supermassive black hole in an ultra-compact dwarf galaxy.
Found in the centre of Fornax UCD3, the black hole is a part of a Fornax galaxy cluster and belongs to a very rare and unusual class of galaxies, the astronomers said, called ultra-compact dwarfs, or UCDs.
"The mass of such dwarf galaxies reaches several dozen millions of solar masses and the radius, typically, does not exceed three hundred light years," the University said.
"This ratio between mass and size makes ultra-compact dwarf galaxies the densest stellar systems in the Universe."
In the presence of a massive body such as a black hole the stars are influenced by its gravity and accelerate in various directions
According to the researchers, the black hole mass is 3.5 million that of the Sun, similar to the central black hole in our own Milky Way.
The study that uncovered the black hole saw the scientists collecting data using SINFONI, an infrared integral field spectrograph installed at one of the eight-metre Very Large Telescopes (VLTs) in Chile, and operated by the European Southern Observatory.
"Having analysed the observed spectra, [we] derived the dependence between stellar velocity dispersion and radius in Fornax UCD3," said the astronomers.
Velocity dispersion quantifies the average variation between the individual stellar line-of-sight velocity and the mean velocity of the entire stellar population.
Velocity dispersion in its centre is so high that it can only be explained by the presence of a massive central black hole
"In the presence of a massive body such as a black hole the stars are influenced by its gravity and accelerate in various directions," the report explained.
"Due to that their average speed does not grow but the dispersion increases considerably. This is the very effect that was observed in this galaxy: the velocity dispersion in its centre is so high that it can only be explained by the presence of a massive central black hole."
After that the scientists compared the dependence of velocity and dispersion with dynamic models based on different assumptions of the black hole mass. They found that the model suggesting the mass of the black hole being equal to 3.5 million solar masses agreed with the observations best.
The black hole discovered by the authors is the fourth ever to be found in UCDs and corresponds to 4 per cent of the total galaxy mass.
Anton Afanasiev, the first author of the article, a student of the Department of the Faculty of Physics, MSU, said: "To be able to say with complete assurance that this hypothesis is correct, we need to discover more supermassive black holes in UCDs. This is one of the prospects of this work."
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