Planets Can Form In The Center Of Violent, Unstable Galaxies
September 12, 2012

Planets Can Form In The Center Of Violent, Unstable Galaxies

April Flowers for - Your Universe Online

Listen to the podcast “How Planets Form” with redOrbit's Dr. John Millis and planet-hunting expert Dr. Eric Mamajek of the University of Rochester.

The center of the Milky Way seems like the last place to form a new planet, inhospitable and violent even. Stars crowd each other, whizzing through space like cars on a rush hour freeway while supernova explosions blast out shock waves and bathe the region in intense radiation. The very fabric of space is twisted and warped by a supermassive black hole's gravitational forces.

A new study, published in Nature, shows that the planets can still form in this cosmic maelstrom. The research team from the Harvard-Smithsonian Center for Astrophysics point to the recent discovery of a cloud of hydrogen and helium plunging toward the galactic center as proof. They argue that this cloud represents the shredded remains of a planet-forming disk orbiting an unseen star.

"This unfortunate star got tossed toward the central black hole. Now it's on the ride of its life, and while it will survive the encounter, its protoplanetary disk won't be so lucky," said lead author Ruth Murray-Clay.

The cloud was discovered last year using the Very Large Telescope (VLT) at the European Southern Observatory (ESO) in Chile, by a different team of astronomers who speculate that it formed when gas streaming from two nearby stars collided, like windblown sand gathering into a dune.

The VLT is a telescope array, consisting of four Unit Telescopes with main mirrors of 8.2 meters in diameter and four movable 1.8 meter diameter Auxiliary Telescopes, making the VLT the world's most advanced optical instrument. The telescopes can work together to create a giant 'interferometer' allowing astronomers to see details up to 25 times finer than with the individual telescopes.

Murray-Clay and colleagues have a different take on the cloud. Newborn stars retain a surrounding disk of gas and dust for millions of years. If one such star dove towards our galaxy's central black hole, radiation and gravitational tides would rip apart its disk in a matter of years.

The likely source for this stray star is a ring of stars known to orbit the galactic center at a distance of about one-tenth of a light year. Astronomers have detected dozens of young, bright O-type stars in this ring, suggesting that hundreds of fainter Sun-like stars also exist there. Interactions between the stars could fling one inward along with its accompanying disk.

This protoplanetary disk is being destroyed, however the stars that remain in the ring can hold onto their disks and might form planets despite the hostile environment.

As the star continues its plunge over the next year, more and more of the disk's outer material will be torn away, leaving only a dense core. The stripped gas will swirl down into the maw of the black hole. Friction will heat it to high enough temperatures that it will glow in X-rays.

"It's fascinating to think about planets forming so close to a black hole," said Loeb. "If our civilization inhabited such a planet, we could have tested Einstein's theory of gravity much better, and we could have harvested clean energy from throwing our waste into the black hole."