April 5, 2013
Astronomers Find Surprising Star Formation Near Supermassive Black Hole
Brett Smith for redOrbit.com - Your Universe Online
The entire Milky Way galaxy revolves around a supermassive black hole, which is surrounded by a turbulent expanse of space fraught with extreme gravitational forces.Despite the inhospitable nature of this region, a team of American astronomers has found jets of material that typically indicate star formation when found in less tumultuous sections of the universe, according to their report in the Astrophysical Journal Letters.
"People think it is very hard to form stars near a supermassive black hole," explained co-author Farhad Yusef-Zadeh of Northwestern University.
"This is because the gravity of the black hole produces extreme tidal forces that would stretch and elongate molecular clouds, preventing them from ever accumulating enough mass to trigger star formation. But what we seem to have found are patches of dust and gas that have become so dense that they are able to overcome their inhospitable surroundings."
Based on their observations using the Atacama Large Millimeter/submillimeter Array (ALMA), the team of astronomers said central black hole´s orbiting molecular clouds have become so massive and dense that they often collide and start a chain of events that leads to the birth of a new star.
During the star formation process, material in these clouds bonds closely together, causing the increasingly denser mass to rotate faster and faster. As the star begins to form and its rotation accelerates, some excess stellar material jets out into space.
Using powerful imaging tools like ALMA, astronomers can detect these jets of material by looking for the presence of silicon monoxide (SiO), a molecule that is abundant in molecular clouds. During star formation, SiO enters an excited state and emits a very specific set of wavelengths of microwave energy. ALMA has been specifically calibrated to detect these light wavelengths.
"SiO is an excellent tracer of molecular outflows," said Yusef-Zadeh. "What we see in these images from ALMA are outflows that appear very much like what we see in star-forming regions elsewhere in galaxy.”
“So the environments may be very different, but once you get the right conditions, collapse takes place and you're able to create what we would observe to be run-of-the-mill massive or intermediate mass stars,” he said.
The study provides some clues as to why stars can be seen orbiting the Milky Way´s central and most massive black hole. For years, astronomers have been trying to determine why these young stars exist in an area of space where they theoretically should not be. Previous theories stated that either the young stars formed elsewhere and moved inward or they somehow overcame their tumultuous births to become typical stars.
"Though this question of stars near the galactic center is still open ended, ALMA will definitely have the power and sensitivity to shed more light on the mystery," said co-author Al Wootten, the North America ALMA Project Scientist with the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia. "These latest studies do suggest that the conditions necessary for star formation could extend much closer to the galactic center than we previously believed."