Astronomers Say Planets Can Form in Milky Way’s Center

A research led by Dr Ruth Murray-Clay of the Harvard-Smithsonian Center for Astrophysics shows that planets can form in the center of our galaxy.

Artist’s conception of a protoplanetary disk of gas and dust, red, is being shredded by the powerful gravitational tides of our galaxy’s central black hole (David A. Aguilar / CfA)

For proof, the astronomers point to the recent discovery of a cloud of hydrogen and helium plunging toward the Milky Way’s center. They argue that this cloud represents the shredded remains of a planet-forming disk orbiting an unseen star. The findings are published in the journal Nature.

“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,” Dr Murray-Clay said.

The cloud in question was discovered in 2011 by a team of astronomers using the Very Large Telescope in Chile. They speculated that it formed when gas streaming from two nearby stars collided, like windblown sand gathering into a dune.

The new study proposes a different explanation. Newborn stars retain a surrounding disk of gas and dust for millions of years. If one such star dived toward our galaxy’s central black hole, radiation and gravitational tides would rip apart its disk in a matter of years.

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

Although this protoplanetary disk is being destroyed, the stars that remain in the ring can hold onto their disks. Therefore, they may form planets despite their hostile surroundings.

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 co-author Dr Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics. “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.”

_______

Bibliographic information: Ruth A. Murray-Clay, Abraham Loeb. 2012. Disruption of a proto-planetary disc by the black hole at the milky way centre. Nature Communications 3, article number: 1049; doi: 10.1038/ncomms2044