Black Holes Came Before Galaxies

Jan. 9, 2009 -- Evidence is mounting that black holes predate their host galaxies, astronomers announced this week.

Scientists used radio telescopes to determine the mass of distant ancient galaxies by measuring how fast they spin. The galaxies are among the oldest known structures, having formed about 1 billion years after the birth of the universe about 13.7 billion years ago.

The spin rates are directly tied to how much mass the galaxies contain. Like their younger siblings, the galaxies are believed to contain black holes -- and rather large ones, judging by much visible and near infrared light they are triggering.

Yet when astronomers matched up the size of the black holes to the galaxies' mass, the proportions were way off.

"In the early universe, the ratios are different," Chris Carilli, with the National Radio Astronomy Observatory in New Mexico, told Discovery News.

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Typically, a galaxy has about 1,000 times more mass in its central bulge of stars than what is contained inside its black hole. Yet, four distant galaxies studied by Carilli and an international team of colleagues turned out to have black holes 20 to 30 times larger than expected, prompting the team to theorize that the black holes came before the galaxies formed.

"The simplest conclusion is that the black holes come first and somehow grow the galaxy around them ... that's sort of the bottom line here," California Institute of Technology's Dominik Riechers said at the American Astronomical Society conference in Long Beach, Calif., this week.

Carilli's team measured the rotational spin of molecular gas associated with four very distant radio galaxies known as quasars. Princeton astronomer Michael Strauss was part of a team that initially discovered some of the targets.

"We didn't see a huge amount of evidence for stars," Strauss told Discovery News. "When you measure the mass of the gas and the mass of the black hole, there is no mass left for star systems."

Carilli's team has been using radio telescopes in New Mexico, France and Spain to make their observations.

"These are very difficult measurements to make, requiring tens to hundreds of hours," he said.

The work should get a lot easier -- and more interesting -- when work to upgrade the Very Large Array in New Mexico and construction of a new highly sensitive radio telescope in Chile is complete in three to four years.

"We'll put 100, maybe 1,000 points on that plot," Carilli said. "I'm extremely hopeful."

Related Links:

Irene Klotz's Blog: Free Space

Discovery Space's Dave Mosher blogs on the finding.

How Stuff Works: Galaxy Formation