Astronomers have discovered the closest black hole to Earth. It’s so close its sister stars can be seen with the naked eye. Wednesday’s announcement backs up the theory that there are lots of these small black holes in our galaxy but we just don’t see them. Black holes usually can only be seen if astronomers spy star stuff falling into them but most of the time nothing is close enough to fall in. The newly discovered black hole isn’t close enough to nibble at its two sister stars, but it is warping one star’s orbit. That allows astronomers to find it.