Black holes are quite common (estimates indicate over 10 million in the Milky Way alone), and now it doesn’t appear that you have to go very far to find one... relatively speaking. Astronomers have detected what they say is the closest known black hole to date, a stellar-mass object in the double-star HR6819 system about 1,000 light-years away. The team discovered the hole after noticing that the stars were orbiting an invisible object, and using calculations on the inner star’s orbit to determine that the mass was at least four times that of the Sun — it had to be a black hole.
The researchers used a spectrograph on the MPG/ESO 2.2-meter telescope to study the system over the course of several months.