Astronomers have been able to identify one of the lowest mass supermassive black holes ever observed in the middle of a galaxy, thanks to NASA’s Chandra X-ray Observatory and several other observatories.
The host galaxy is of a type not expected to harbour supermassive black holes, suggesting that this black hole, while related to its supermassive cousins, may have a different origin.
The black hole is located in the middle of the spiral galaxy NGC 4178, located about 55 million light-years from Earth.
An analysis of the Chandra data, along with infrared data from NASA’s Spitzer Space Telescope and radio data from the NSF’s Very Large Array, suggests that the black hole is near the extreme low-mass end of the supermassive black hole range.
The properties of the X-ray source, including its brightness and spectrum — the amount of X-rays at different wavelengths — and its brightness at infrared wavelengths, suggest that a black hole in the center of NGC 4178 is rapidly pulling in material from its surroundings.
The same data also suggest that light generated by this infalling material is heavily absorbed by gas and dust surrounding the black hole.
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.
This method gives a black hole mass estimate of less than about 200,000 times that of the Sun. This agrees with mass estimates from several other methods employed by the researchers, and is lower than the typical values for supermassive black holes of millions to billions of times the mass of the Sun.
The discovery was recently published in The Astrophysical Journal.