Science News Review

The Chicken-Egg Question Goes Galactic

Jan 12 at 6:06pm by Aileen

Hi-res infrared composite of galactic core

Atronomers and astrophysicists determined some years ago – after that strange beastie known as a “black hole” was accepted to probably be a real physical phenomenon, that there are gigantic black holes at the center of galaxies. Moreover, they found they could determine the mass of these galactic black holes via a fairly simple ratio between the mass of the central bulge of stars and the hole they surround (about 1:10,000). It has been presumed that the hole at the galactic center got there by the joining of stellar mass black holes, which then continued to grow by accretion of mass from the stars drawn into the gravity well.

More recently, however, scientists examining galaxies much farther away in space and time found a different pattern. The farther back into the history of the universe they looked, the ratio between galactic black holes and the mass of the stars surrounding them did not follow the 1:10,000 ‘rule’ – the holes account for much more of the mass, meaning they were huge even way back in the early days of the universe.

As quoted in Wired’s article Yo Galaxy’s Mama Is a Black Hole, astronomer Chris Carilli of the National Radio Astronomy Observatory said during a briefing at the American Astronomical Society’s annual meeting that “The simplest conclusion is that the black holes come first and they somehow grow the galaxy around them.”

Supermassive galactic black holes have been noted in galaxies as early as 1.7 billion years after the Big Bang, or 12 billion years ago as seen by us from here on planet earth. These might be survivors of “Primordial Black Holes” theorized to have been created by conditions of the Big Bang, which began to merge after inflation and draw to themselves ever increasing amounts of matter that formed into galaxies. Or some other origin may become apparent with further study, to be greatly enhanced by the Expanded Very Large Array radio telescope system [EVLA] in New Mexico and the Atacama Large Millimeter / submillimeter Array [ALMA] in Chile, which should be completed by 2012.

In other news, the region of our own galaxy’s core has been detailed in high resolution infrared by a composite panorama made up of snapshots by the Hubble and Spitzer space telescopes. “Hi-res” in this instance, covering an area 300 x 115 light years 26,000 light years away from here (and now) means being able to see objects as ’small’ as just 20 times the size of our solar system. Which is quite a feat, and offers an awe-inspiring glimpse of conditions near the core that should make us glad we live way out here in our relatively peaceful long arm of the galaxy instead.

Our home galaxy (the Milky Way) has also grown by 50% recently, though not by accumulating mass or anything. New measurements of how quickly our galaxy is rotating in space led a team of astrophysicists from Harvard to conclude that the mass that makes up our galaxy is 50% larger than previously believed. It may also have four arms instead of two, which would make us look to an observer in Andromeda more like a pinwheel instead of a spiral.

And while the new measurements may serve to inflate our cosmic ego a bit, it also bodes ill for the future if astronomers are correct in projecting that a heavier Milky Way will inevitably collide with its neighbor Andromeda sooner than it otherwise would have.

Links:

Yo Galaxy’s Mama Is a Black Hole
Did the big bang spawn trillions of black holes?
Black Holes Grew Fast, Merged Early
Milky Way 50 Percent Larger
Expanded Very Large Array
Atacama Large Millimeter / submillimeter Array