Black holes may precede galaxies, astronomers say
WASHINGTON (Reuters) - Black holes -- those massive, invisible objects that suck in everything around them -- may have appeared before the galaxies that host them, astronomers said on Wednesday.
The findings could change the understanding of how galaxies first formed, and what role black holes play in the universe.
Most or all galaxies are believed to have black holes at their centers. Just last month astronomers confirmed that our own Milky Way galaxy has a black hole at its center.
Researchers told a meeting of the American Astronomical Society in Long Beach, California, that they had seen a clear link between the size of a black hole, as measured by its mass, and the galaxy where it was found.
A black hole's mass is about one one-thousandth of the mass of the surrounding galactic bulge, they said.
"This constant ratio indicates that the black hole and the bulge affect each others' growth in some sort of interactive relationship," said Dominik Riechers of the California Institute of Technology, or Caltech.
"The big question has been whether one grows before the other or if they grow together, maintaining their mass ratio throughout the entire process."
The researchers used the Very Large Array telescope in New Mexico and other instruments to compare nearby, and younger, black holes to those that are farther away and thus older. They have seen back close to the Big Bang, 13.7 billion years ago.
"We finally have been able to measure black-hole and bulge masses in several galaxies seen as they were in the first billion years after the Big Bang, and the evidence suggests that the constant ratio seen nearby may not hold in the early universe," said Fabian Walter of the Max-Planck Institute for Radioastronomy in Germany.
"The black holes in these young galaxies are much more massive compared to the bulges than those seen in the nearby universe," Walter added in a statement. "The implication is that the black holes started growing first."
What is not understood is how the birth of a black hole might have affected the formation of a galaxy, the astronomers told a news conference and telephone briefing.
"To understand how the universe got to be the way it is today, we must understand how the first stars and galaxies were formed when the universe was young," said Chris Carilli of the National Radio Astronomy Observatory.
For one thing, the light from the black holes outshines any surrounding stars, making them difficult to see.
"With the new observatories we'll have in the next few years, we'll have the opportunity to learn important details from the era when the universe was only a toddler compared to today's adult," Carilli said.
(Reporting by Maggie Fox; Editing by Will Dunham and Eric Walsh)
