Astronomers Identify a New Class of Black Holes

Globular cluster 47 based on data from FORS1. (Credit: ESO) Some black holes are small. Some black holes are giant. But oddly enough, in the cosmic fight between innocent passing stars and voracious black holes, scientists have never found a mid-sized black hole. Until now. The star cluster 47 Tucanae, located about 13,000 to 16,000 light years from Earth, is a dense ball of stars. Hundreds of thousands of stars compacted into a 120 light-year span give off gamma rays and X-rays and more energetic events, but to date, no black holes had been found there. The center seemed ripe for opportunities to find one, but a lack of tidal disruption events and a jumble of stars hard to sift through obscured finding any lurking black holes there. The Harvard-Smithsonian Center for Astrophysics turned to two tactics to find the black hole instead. First, they observed the motion of the ...