January 28, 2014
Active Supermassive Black Holes Discovered In Two Merging Galaxies
[ Watch the Video: Galaxy Mergers And Supermassive Black Holes ]
Lee Rannals for redOrbit.com - Your Universe OnlineAstronomers publishing a paper in the Astrophysical Journal say they have found two merging galaxies have active supermassive black holes.
The team conducted infrared observations of the merging galaxies by using the Subaru Telescope. They found that at least one of the supermassive black holes almost always becomes active and luminous by accreting a large amount of material.
The study suggests local physical conditions near the supermassive black holes rather than general properties of galaxies primarily determine the activation of the mysterious objects.
The widely accepted galaxy formation scenario says collisions and mergers of small gas-rich galaxies result in the formation of massive galaxies seen in the current Universe. Previous studies have shown that supermassive black holes with more than one-million solar masses are found in the center of galaxies. A solar mass is a standard unit of mass in astronomy and uses the mass of our sun as a base, which is about 332,946 times more massive than Earth.
Merging gas-rich galaxies with these huge black holes in their centers causes active star formation, and also stimulates mass accretion onto the supermassive black holes. When the material accretes onto a supermassive black hole, the accretion disk around it becomes hot from the release of gravitational energy, making it become very luminous. This process is referred to as active galactic nucleus activity and is different from the energy generation activity by nuclear fusion reactions within stars.
Scientists need to understand the differences with active galactic nucleus activity and energy generation activity by nuclear fusion to help clarify the physical processes of galaxy formation. However, it has been difficult for scientists to make observations of these processes because dust and gas shroud their view.
Astronomers at the National Astronomical Observatory of Japan (NAOJ) used the Subaru Telescope’s Infrared Camera and Spectrograph and its adaptive optics system to observe infrared luminous merging galaxies at the infrared K-band and L-band. This tool helped the team peer beyond the gas and dust to get a better look at what is taking place inside these merging galaxies.
The team found that not all supermassive black holes in gas-rich merging galaxies are actively mass accreting, and that multiple black holes have considerably different mass accretion rates.
This study demonstrated that local conditions around supermassive black holes rather than general properties of galaxies dominate the mass accretion process onto the black holes.
Image Below: Examples of infrared K-band images of luminous, gas-rich, merging galaxies. The image size is 10 arc seconds. North is up, and east is to the left. The individual images clearly show aspects of the merging process, such as interacting double galaxy nuclei and extended/bridging faint emission structure. Credit: NAOJ