We just found the first one within 1,000 light-years of us. But there’s probably one much, much closer.
For a long time, black holes were known to exist only in the imaginations of theorists.
With enough mass concentrated into a small enough volume, not even light moves fast enough to escape.
First predicted in 1916 in General Relativity, the first one wasn’t discovered in space until 1964: Cygnus X-1.
When black holes orbit another object, they can siphon and accelerate matter, creating X-ray and radio signatures.
Black holes also gravitate; we can infer a black hole’s presence as it influences its companions.
We later discovered X-ray and radio emissions from galactic centers, indicative of supermassive black holes.
Even without visible companions, we’ve identified dozens of black holes directly: through their gravitational waves.
Sagittarius A*, at the center of the Milky Way, is the closest supermassive black hole, some 25,000 light-years distant.
A smaller one — just 6.6 solar masses — orbits a Sun-like star just 3,500 light-years away: V616 Monocerotis.
That distance record was shattered last week, by trinary system HR 6819: two stars and a black hole 1,000 light-years distant.
It’s the only black hole-containing system visible to the naked eye.
As our methods and surveys continue to improve, closer black holes will inevitably be discovered.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.