On September 16, 2012, NASA’s Swift satellite caught an x-ray outburst, believed to have come a flood of gas plunging toward a previously unknown black hole. This new black hole in our Milky Way galaxy has been designated as Swift J1745-26 by astronomers.
Black holes such as this one are thought to be common in our galaxy, but we don’t see very many of them. This is the first one discovered by the Swift satellite. The video above – from NASA’s Goddard Space Flight Center – shows how Swift made the discovery. This black hole has a sun-like companion star. Gas flowing from the companion collects into a disk around the black hole. Normally, this gas would steadily spiral inward. But in this system, the gas collects for decades before suddenly surging inward, causing the x-ray outburst detected by Swift.
Often when astronomers speak of black holes, they are speaking of supermassive objects thought to be located at the center of most galaxies, including our own Milky Way. Supermassive black holes may have the mass of a billion suns. But stellar-mass black holes are very different, much less massive, formed from individual stars. The first stellar-mass black hole candidate was Cygnus X-1, which, not coincidentally, is one of the strongest X-ray sources seen from Earth. Cyg X-1 is now estimated to have a mass about 14.8 times the mass of our sun.
Today, by understanding how stars evolve and by estimating how many stars have enough mass to evolve into black holes, astronomers deduce that our galaxy has some 100 million stellar-mass black holes. We don’t see these objects, but astronomers believe they exist.
Astronomers do now study about a dozen stellar-mass black hole candidates in our Milky Way, including Cygnus X-1 and now Swift J1745-26. The nearest one is about 1,600 light-years from Earth, according to hubblesite.org.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.