Universe's Most Massive Black Holes Got Huge Early

The first rapid growth spurt of the universe's most massive black holes occurred much earlier than astronomers previously thought, and are still growing fast, a new study finds.

A team of astronomers from Tel Aviv University in Israel determined that the first period of fast growth of the most massive black holes occurred when the universe was only about 1.2 billion years old ? not 2 to 4 billion years old, as had been thought. Astronomers estimate the universe is about 13.7 billion years old.

In the study, astronomers also determined that the universe's oldest and most massive black holes are also growing at a very fast rate. The findings will be detailed in an upcoming issue of the Astrophysical Journal. [Photos: Black Holes of the Universe]

Black hole giants

Most galaxies in the universe, including our own Milky Way, harbor supermassive black holes at their center. These black holes vary in mass from about one million to about 10 billion times the mass of the sun.

To detect these giants, astronomers look for the enormous amount of radiation emitted by the gas that falls into the black holes when they are actively accreting matter. This gas pouring into massive black holes is thought to be the means by which they grow.

The new research is based on observations from some of the largest ground-based telescopes in the world: Gemini North, located on top of Hawaii's Mauna Kea volcano, which rises more than 13,000 feet (over 4,000 meters) above sea level; and the Very Large Telescope Array, atop Cerro Paranal in Chile.

How heavyweight black holes get big

The observations showed that the black holes that were active when the universe was 1.2 billion years old are about 10 times smaller than the most massive black holes that are seen at later times. They are, however, growing at a much faster rate, which would make them much more massive now than their later counterparts.

By measuring the rate of growth, the researchers were able to estimate what happened to these objects at much earlier and much later times.

The team found that the very first black holes ? those that started the entire growth process when the universe was only several hundred million years old ? had masses of only 100 to 1,000 times the mass of the sun.

These black holes may be related to the very first stars in the universe, researchers said.

The astronomers also found that the subsequent growth period of these observed black holes, after the first 1.2 billion years, lasted only 100 to 200 million years.

The new study is the culmination of a seven-year-long project at Tel Aviv University designed to follow the evolution of the most massive black holes and to compare them with the evolution of the galaxies in which they reside.

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