Yo Galaxy's Mama Is a Black Hole

Lurking deep inside the center of almost all galaxies is a ravenous, super-massive black hole, and new research suggests the black hole may have given birth to its galaxy. This could be the answer to a long-standing astronomical chicken-and-egg problem.

By observing a series of galaxies and measuring the motions of swirling gas inside them, astronomers were able to weigh the galaxies and their resident black holes. They found that in general, there is a direct relationship between the size of a black hole and the size of the central bulge of stars and gas in the galaxy around it: Black holes usually weigh about one one-thousandth of the mass of the galactic bulge.

But when the researchers looked at galaxies that were farther away, and thus effectively dating from earlier periods in the universe’s history (because the more distant we look, the longer an object’s light has taken to reach us, so the older it is), they found a surprising pattern.Blackhole

The usual mass ratio between black hole and galaxy didn’t hold up. Instead, the black holes in the farthest away galaxies — the ones we are seeing in the youngest stage of development — were much larger than expected.

"The simplest conclusion is that the black holes come first and they somehow grow the galaxy around them," said astronomer Chris Carilli of the National Radio Astronomy Observatory during a briefing Wednesday at the American Astronomical Society's meeting in Long Beach, California.

If this is true, it raises many significant questions about why the black holes and galaxies are so linked, and how black holes help galaxies grow.



"We don't know what mechanism is at work here, and why, at some point in the process, the 'standard' ratio between the masses is established," said Caltech astronomer Dominik Riechers in a press release. Riechers also worked on the study.

Some theorize that the strong winds and jets surrounding black holes could help feed star formation and induce galaxies to grow. But the violent environments of black holes have also been thought too chaotic to harbor stable star formation.

The researchers hope to better understand the seemingly symbiotic relationship between galaxies and their gobbling black hole inhabitants when new observation tools come online soon. The Expanded Very Large Array (EVLA) being built in New Mexico, and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, expected to be completed by 2012, should dramatically increase the sensitivity and resolution available for studies of distant galaxies.

"We really do need to confirm this with further observations," Carilli said. "In fact the future looks extremely bright for these kinds of studies."