By combining observations from NASA’s Chandra X-ray Observatory with infrared data from NASA’s Spitzer Space Telescope and radio data from the NSF’s Very Large Array, a black hole in the center of the spiral galaxy NGC 4178 has been determined to be one of the lowest mass supermassive black holes ever observed in the middle of a galaxy.
This SDSS visible-light image shows the spiral galaxy NGC 4178. The inset shows an X-ray source at the position of the black hole in the NGC 4178’s center (X-ray: NASA / CXC / George Mason Univ / N.Secrest et al, optical: SDSS)
NGC 4178 is a spiral galaxy located some 55 million light years from Earth. An analysis of data from three telescopes, published in the Astrophysical Journal (arXiv.org version), shows that the black hole in the NGC 4178’s center is near the extreme low-mass end of the supermassive black hole range.
The properties of the X-ray source suggest that this black hole is rapidly pulling in material from its surroundings, and that light generated by this infalling material is heavily absorbed by gas and dust surrounding the black hole.
A team of astrophysicists led by Dr Nathan Secrest of the George Mason University in Fairfax used a known relationship between the mass of a black hole and the amount of X-rays and radio waves it generates to estimate the mass of the black hole.
The results show that the object has a mass less than about 200,000 times that of the Sun. This agrees with mass estimates from several other methods employed by the team, and is lower than the typical values for supermassive black holes of millions to billions of times the mass of the Sun.
Previously, astronomers have found that observations of a large number of galaxies are consistent with a close correlation between the mass of a supermassive black hole and the mass of the bulge of its host galaxy. Theoretical models developed to explain these results invoke mergers of galaxies, and predict that galaxies without bulges are unlikely to host supermassive black holes.
The observations also revealed three other X-ray sources. If they are located in NGC 4178 they are likely to be binary systems containing a black hole or neutron star. The brightest of the three sources may be an intermediate-mass black hole with a mass that is about 6,000 times that of the Sun.
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Bibliographic information: Secrest N.J. et al. 2012. The Chandra View of NGC 4178: The Lowest Mass Black Hole in a Bulgeless Disk Galaxy? ApJ, vol. 753, no. 1, 38; doi: 10.1088/0004-637X/753/1/38
