Which came first: galaxies or black holes?

Supermassive black holes at the centre of galaxies may form before the galaxies themselves, a new study has found.

The central bulge of a galaxy usually has a thousand times more mass than the black hole at its centre, but that this isn’t the case in very young galaxies, an international team reported yesterday to a meeting of the American Astronomical Society in Long Beach, California.

Efficient growth

Instead, the black holes are relatively much larger in baby galaxies, hinting that the holes came first. That changes the way astronomers will think about the growth and evolution of galaxies, according to team member Dominik Riechers.

“Our findings show that… a simple regulating process that allows simultaneous growth cannot be the only reason for the relationship [between black holes and bulges],” said Riechers, an astronomer at California Institute of Technology in Pasadena, USA.

“Even if we look at the most extreme, rapid star-forming events in the universe, those are less [fast and] efficient than the growth of massive black holes,” he said.

To make the discovery, Reicher’s team studied conditions during the first billion years of the universe using the Very Large Array radio observatory in New Mexico, and the Interferometer at Plateau de Bure in France.

Time travel

These telescopes are able to see galaxies that are so far away that they appear as they did during the first billion years of the universe’s existence.

It appears that all ‘spheroidal’ galaxies have a supermassive black hole at the centre, Riechers said, and until now, astronomers had observed that the black hole’s mass was always about one thousandth of the mass of the galaxy’s dense central bulge of stars.

This correlation suggested to scientists that the same physical process must regulate the growth of both black holes and the galaxies that surround them, but the new findings show that other forces must be at work as well.

It also helps solve a galactic chicken-and-egg problem: do galaxies form around black holes, or do black holes grow up inside existing galaxies?

Read more here Which came first: galaxies or black holes? | COSMOS magazine.

This entry was posted in Cosmology. Bookmark the permalink.