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article imageSupermassive black holes are growing faster than thought

By JohnThomas Didymus     Feb 14, 2013 in Science
A new study shows that supermassive black holes at the center of galaxies are growing at a much faster rate than thought. The study suggests SMBHs do not grow primarily by galactic mergers as previously thought but by absorbing matter piecemeal.
Supermassive black holes (SMBHs) are found at the centers of galaxies and can have mass from one million to one billion times the Sun.
A new research paper titled "Disk Assembly and the M BH-σ e Relation of Supermassive Black Holes," published in the Astrophysical Journal, shows that SMBHs holes are growing at much faster rates than previously thought possible. The researchers found that even the relatively quiet black hole at the center of our Milky Way Galaxy may be growing by consuming the mass equivalent of one Sun every 3000 years.
Astronomers have assumed until recently that black holes grow almost exclusively through galactic mergers that occur when galaxies collide.This theory of formation and growth of SMBHs suggested that they do not grow significantly by other means beside galactic mergers. This led to the conclusion that the SMBH at the center of our galaxy could hardly be growing.
A research team led by Victor Debattista of the University of Central Lancashire, England built computer simulations to investigate how SMBHs grow, especially in spiral galaxies like ours where galactic mergers are not occurring. The simulation yielded the surprising result that contrary to long held scientific theory, SMBHs at the center of the galaxies can grow very rapidly even in spiral galactic environments like the Milky Way that are not experiencing galactic mergers. The SMBHs in galaxies such as ours grow at a surprisingly fast rate simply by feeding on galactic gas and other matter.
The simulation showed that the growth of SMBHs in merger-free spiral galactic environments can be very fast indeed. According to the study, the black hole at the center of the galactic-merger free Sombrero, M104 or NGC 4594 Galaxy (see image below) has swallowed the mass equivalent of one sun every 20 years and has grown to at least 500 million solar masses.
The researchers said that the supermassive black hole Sagittarius A* at the center of our galaxy appears be growing at a much more modest rate of one solar mass every 3,000 years. Scientists estimate the mass of Sagittarius A* at about 4 million Suns.
Sombrero  M104 or NGC 4594 Galaxy
Sombrero, M104 or NGC 4594 Galaxy
NASA
Astronomers have also recently identified a gas cloud near the center of or galaxy that will be swallowed by SMBH Sagittarius A*. It is believed that the black hole will rip the gas cloud apart in the next 10 years, absorbing up to about 15 times the mass of the Earth.
The new study by Debattista et al. further strengthens the suggestion from new evidence that growth of SMBHs through galactic mergers are the exception rather than the rule.
Supporting the research finding are recent observations by the Hubble Space Telescope that indicate that black holes can grow even in merger-free spiral galaxies.
Lead author Victor Debattista, said: "These simulations show that it is no longer possible to argue that black holes in spiral galaxies do not grow efficiently. Our simulations will allow us to refine our understanding of how black holes grew in different types of galaxies."
The team of researchers included Dr Stelios Kazantzidis of Ohio State University and Professor Frank C. van den Bosch of Yale University. The constructed the computer simulation using a property of black holes first discovered by the Hubble Space Telescope. Data from the Hubble Space Telescope showed that masses of SMBHs can be accurately calculated from the speed of stars in their galaxies.
The new research study appears to disprove the previous theory that black holes are unable to grow in a galaxy that is growing.
The study authors said: "Our simulations will allow us to refine our understanding of how black holes grew in different types of galaxies."
The study was published on Feb. 12 by The Astrophysical Journal.
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