Astronomers have accidentally discovered the closest known black hole to Earth, and it beats the old record by quite a bit: This one is only about 1,000 light years away (the previous record holder is probably about 3,000 light years away). In a galaxy 120,000 light years across that’s pretty close!
To be clear, and because I know a lot of people get anxious about such things: This black hole is way too far away to hurt us in any way. In fact, the reason it's been undiscovered for so long is because it's so placid!
It was found because it's part of a multiple star system. The Sun is a solo star, but a large fraction of stars in the galaxy are in multiple systems: binaries, trinaries, and so on. Some systems even have seven stars in them.
HR 6819 was a known binary already, though a weird one. The two stars are close enough together that from Earth they blend into one (like the headlights on a distant car on the highway look like a single dot). Both stars are what we call B type stars: hotter, more massive, bluer, and more luminous than the Sun. However, while ...