Gas Cloud Hurtling toward Milky Way’s Black Hole May Harbor Young Star
By Ron Cowen of Nature magazine
A gas cloud that is careering towards the supermassive black hole at the centre of the Milky Way may be the visible trail of a planet-forming disk surrounding a young, low-mass star, astrophysicists propose.
Modeling work by Ruth Murray-Clay and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, suggests that planets can form within the powerful gravitational field of a giant black hole. And it heightens expectations about what astronomers might learn as the cloud nears the galaxy’s biggest black hole — an event expected to cause a spectacular light show that could begin as early as next year. The model is published today in Nature Communications.
Murray-Clay and Loeb began their study last autumn after hearing one of the first public talks about the gas cloud. The team that discovered it proposed that the cloud formed when gas flowing out from two stars collided. But Murray-Clay and Loeb immediately seized on the idea that the cloud’s mixture of gas and ionized dust might come from a planet-forming disk surrounding a single young star.
The idea isn’t as far-fetched as it might sound, because a ring of young stars is known to orbit at about 0.03 parsecs (one-tenth of a light year) from Sagittarius A*, the black hole of four million solar masses that lies at the Milky Way’s centre. In star-forming regions throughout the Galaxy, young stars often have planet-spawning disks, and Murray-Clay and Loeb reasoned that those in the region immediately surrounding a black hole might be no different.
According to their model, gravitational interactions dislodged a young, low-mass star orbiting near the ring’s inner edge. The ejected star, now heading towards Sagittarius A*, is too small and faint to be detected. However, material from the star’s disk — boiled off by ultraviolet radiation from other young stars and then stretched out by the black hole’s tidal gravitational forces to form an elongated cloud — can be observed.