In January 2011, astronomers discovered the largest black hole yet. Black hole M87 is 50 million light-years away, and has an astounding mass, about 6.8 billion times that of our own sun.
Black holes are small regions of space so dense that their gravity pulls in even light. They are believed to form during the supernova and collapse of exceptionally large blue giant stars. They then travel through space, gradually accumulating more and more mass as they pull in nearby matter. The largest black holes, known as supermassive black holes, lie at the center of galaxies, including the Milky Way Galaxy. Current theories suggest that most or even all galaxies have a supermassive black hole in their core. Many astronomers believe they have even identified the black hole at the center of the Milky Way, a radio source named Sagittarius A*. Sagittarius A* cannot be seen visibly because it is blotted out by the dust clouds found between our solar system and the center of the galaxy about 26,000 light years away. It seems to have a mass about four million times that of the sun.
The Milky Way’s supermassive black hole is massive, but it is easily dwarfed by other supermassive black holes. According to Daily Galaxy, the newly discovered black hole lies at the center of galaxy Messier 87 (M87), an enormous elliptical galaxy located about 54 million light-years from Earth. Astronomers in Hawaii, working at the Gillett Gemini Telescope, have calculated its mass at about 6 billion solar masses, or about 1500 times as large as the supermassive black hole in the Milky Way Galaxy. A black hole that size, says Karl Gebhardt of the University of Texas (who led the study,) would “swallow (our) solar system whole.” More specifically, a black hole of that mass would have a diameter of about 20 billion kilometers, or twice as far out as the orbit of the planet Neptune.
Astronomers actually knew about black hole M87 prior to the most recent study, but had not been able to estimate accurately how large it was. Gebhardt’s team estimated the velocities of the stars that orbit it, and found they were traveling more than twice as fast as our own sun is traveling. From there, they were able to extrapolate the mass of the black hole those stars were orbiting.
It’s not certain how long black hole M87’s record will last. In 2008, New Scientist reported that a black hole in quasar OJ287, an astounding 3.5 billion light years away, might have a mass as great as 18 billion suns. This would be far larger than M87, but astronomers are still having trouble pinpointing just how big OJ287 really is, so for the moment, it doesn’t show up in the rankings.