While solitary black holes should be common, they are hard to find. The one in Sagittarius revealed itself when it passed in front of a dim background star, magnifying the star’s light and slowly ...

In a baffling cosmic mystery, astronomers have reported a star that appeared to vanish without a trace. One night it was there, shining bright—and the next, it was gone. No explosion, no fading, no ...

The quasi-periodic eruptions of X-rays from a black hole 300 million light-years away are unlike any researchers have ever seen before.

A distant galaxy that lay quiet for decades has suddenly stirred, lighting up in dramatic bursts that have caught astronomers ...

A mysterious black hole in a distant galaxy just woke up after decades of silence—and it’s putting on a cosmic light show! ESA’s XMM-Newton and other X-ray telescopes are capturing massive bursts of ...

Einstein believed that black holes didn't really exist. But they do: that much we know. We don't know much else about them.