Black Holes in the Centers of Even Early Galaxies

Author:  Jessica Kloss
Institution:  Princeton University
Date:  November 2008

A big question in astronomy is whether galaxies in the very early universe looked the same as galaxies today. Astronomers have observed and postulated that most – maybe even all – nearby galaxies have a massive black hole in the center. But would that hold true for galaxies in the early universe? Now, with the keen vision of the Submillimeter Array in Hawaii, Rob Ivison of the UK Astronomy Technology Centre has discovered two very distant galaxies with black holes at their centers. These galaxies are so far away that the light observed is 12 billion years old, a time when galaxies were just beginning to form.

The galaxy 4C60.07 was the first of these two to be discovered, because of its bright radio emission. Such strong emission usually means that there is a quasar (a black hole feeding on its host galaxy) present. Scientists initially thought there was very active star formation going on around this black hole, because they detected the characteristic infrared glow of such active stellar nurseries, which can make 5,000 suns per year.

But the latest research with the Submillimeter Array has corrected this mistaken notion. In fact, the galaxy with a quasar in the center is old and quiescent, with very little star formation. To form stars, a galaxy must have a plentiful supply of gas, and older galaxies have usually used up all the dust in star formation. However, it turns out that 4C60.07 has a very actively star-forming companion galaxy, with plenty of gas to fuel star formation. This galaxy, too, was observed to have a black hole at its center.

"This new image reveals two galaxies where we only expected to find one," said Rob Ivison, who is lead author of the study. "Remarkably, both galaxies contain supermassive black holes at their centers, each capable of powering a billion, billion, billion light bulbs."

These two galaxies are in the middle of a spectacular collision, during which their central black holes will probably merge and form an even bigger black hole. The Submillimeter Array caught the moment when 4C60.07 was in the middle of ripping material from its neighboring, star-forming galaxy (see image) – which explains why initial studies predicted one very active star-forming and radio-emitting galaxy, instead of two vastly different, but close together galaxies.

"These two galaxies are fraternal twins. Both are about the size of the Milky Way, but each one is unique," said Steve Willner from the Harvard-Smithsonian Center for Astrophysics, and co-author of the paper. He adds, "The superb resolution of the Submillimeter Array was key to our discovery."

This discovery offers much-needed insight on galaxies in the early universe. But there are future implications, as well – the interactions of these two Milky Way sized galaxies could very well be a glimpse into the future of our own galaxy.

Written By: Jessica Kloss

Edited by: Jeffrey Kost

Published by: Hoi See Tsao