Astronomers have determined beyond all reasonable doubt that the heart of the Milky Way is a supermassive black hole, two research teams say. Astronomers have inferred the existence of a gravitational monster in the center of our galaxy for years, but the new results are “the best empirical evidence that super-massive black holes do really exist” [CNN], said researcher Reinhard Genzel.
Similar supermassive black holes are thought to form the center of many spiral and elliptical galaxies, and astronomer Robert Massey says the results suggest that galaxies form around giant black holes in the way that a pearl forms around grit. Dr Massey said: “Although we think of black holes as somehow threatening, in the sense that if you get too close to one you are in trouble, they may have had a role in helping galaxies to form – not just our own, but all galaxies” [BBC News]. Massey explains that if a black holes brings enough matter together in a dense cluster, it creates ripe conditions for the formations of stars and galaxies.
The gravity of black holes is so powerful that not even light can escape from them, which makes direct observation of them impossible; researchers instead had to study the stars in the Milky Way’s center to determine whether they were being influenced by a black hole. Or to put it more poetically: Just as swirling leaves caught in a gust of wind can provide clues about air currents, so the stars’ movements reveal information about forces at work at the galactic centre [Telegraph].
Over a period of 16 years, beginning in 1992, researchers monitored 28 stars orbiting the Milky Way’s central region, where the supermassive black hole called Sagittarius A* is thought to lurk. By watching how the central stars orbited Sagittarius A*, to which they are gravitationally bound, the researchers inferred properties of the black hole itself, such as mass and distance [SPACE.com]. They determined that the enormous thing has a mass equivalent to that of 4 million suns, and that it lies 27,000 light-years away from Earth. The new confirmation comes from two separate teams, one in Europe and one in the United States; both studies will be published in upcoming issues of the Astrophysical Journal.
80beats: Researchers Look Into a Black Hole (But Does the Black Hole Look Back?)
DISCOVER: Black Hole Feasts at Milky Way’s Center
DISCOVER: The Mysterious Middle of the Milky Way
Image: ESO/S. Gillessen et al.