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UNT Insider | April 2011 issue | Physics professor on a team to study supermassive black hole growth

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Physics professor on a team to study supermassive black hole growth

From a UNT News Service press release


Ohad Shemmer

In collaboration with an international team of astronomers, a UNT professor has identified the earliest known epoch of fast growth of the supermassive black holes in the universe, coming a step closer to understanding the mysteries of the universe.

Ohad Shemmer, assistant professor of physics, says this discovery is a "missing link" between black holes observed in galaxies today and the first black holes formed due to the explosion of the first stars.

The study is the culmination of a seven-year project -- led by Benny Trakhtenbrot and Hagai Hetzer from Tel Aviv University in Israel -- and included Shemmer and Paulina Lira from the University of Chile. The study was designed to trace the evolution of the most massive known black holes and compare it with supermassive black holes observed in galaxies today. The results of the study were reported in a recently published issue of The Astrophysical Journal.

The researchers observed 40 active galaxies and compared their properties with those of about 50 other active galaxies to find how the black holes were actively growing, or increasing in size by accreting matter from their host galaxies. The team has reported that the era of fast growth occurred when the universe was about 1.2 billion years old and that the subsequent growth period lasted 100 to 200 million years.

Previous reports in 2004 and 2007 by the same group of astronomers found that the era of fast growth must have occurred when the universe was younger than at least 2 to 4 billion years old.

"We are not seeing the first supermassive black holes, but we are seeing the final stage of their adolescence," Shemmer says. "This research helps us to determine what the 'meal schedule' is for supermassive black holes."

The "meal schedule" is a timetable in which the black holes grow in size by accreting matter from their host galaxies.

The research is based on observations taken from the Gemini Observatory in Hawaii and the Very Large Telescope in Chile, which are among the largest ground-based telescopes in the world. The telescopes used infrared spectrographs to determine the masses and the mass accretion rates of the black holes. The team analyzed the data using a method Shemmer first developed while earning his doctoral degree at Tel Aviv University.

A black hole is an extremely dense, massive object that can form in the aftermath of the explosion of a massive star, or a supernova. Its gravitational field is so intense that no matter or electromagnetic radiation can escape. Most galaxies in the universe, including the Milky Way, harbor supermassive black holes in their centers that vary in mass from about 1 million to about 10 billion times the mass of the sun.

Elizabeth Smith with UNT News Service can be reached at Elizabeth.Smith@unt.edu.

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April 2011

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