Supermassive Black Holes Spotted in Merging Galaxy — is One Missing?

Astronomers have visualised the material surrounding two supermassive black holes in merging galaxies in unprecedented detail, but did they find a speculated third black hole in NGC 6240?

Astronomers have used ALMA (Atacama Large Millimeter/submillimeter Array)to build an image of the gas and dust surrounding two supermassive black holes in stunning detail. The black holes are located in the butterfly-shaped galaxy NGC 6240 — located 400 million light-years from Earth — which is being created from the merger of two smaller galaxies.

The ongoing collision is creating a violent and chaotic environment and carrying along with it, the two supermassive black holes, which will eventually collide and merge themselves. The galaxy was also reported to possess a third supermassive black hole in November 2019, spurring the team to also search for another black hole in the system.

Artist impression of the merging galaxy NGC 6240. Image credit: NRAO/AUI/NSF, S. Dagnello

Obtaining images of the material surrounding these supermassive black holes in this oddly-shaped emerging galaxy should help astronomers understand what is happening within NGC 6240 as the process continues. Though the relatively close galaxy has been studied many times in the past, the resulting images have not been of sufficient detail to conduct such research.

This deficiency has been rectified with the use of ALMA, which has allowed astronomers to improve the resolution of images of NGC 6240 by a factor of ten. Thus these new images, with their massively improved resolution, show the structure of the cool gas clouds in the galaxy, including those surrounding the black holes.

An international team of astronomers used ALMA to create the most detailed image yet of the gas surrounding two supermassive black holes in a merging galaxy. Image credit: ALMA (ESO/NAOJ/NRAO), E. Treister; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble

“The key to understanding this galaxy system is molecular gas,” says Ezequiel Treister of the Pontificia Universidad Católica in Santiago, Chile. “This gas is the fuel that is needed to form stars, but it also feeds the supermassive black holes, which allows them to grow.”

The research was presented in two separate papers published in The Astrophysical Journal and the journal The Astrophysical Journal Letters, respectively.