A black hole is an astronomical object with gravity so strong that nothing—not even light—can escape once it passes its event horizon, the boundary around the singularity.
Stellar black holes form when massive stars (∼20× the Sun’s mass) exhaust their nuclear fuel, undergo supernova explosions, and collapse under gravity into a point with extreme density and curvature of spacetime. If the remnant core exceeds roughly three solar masses, no known force can resist the collapse.
Supermassive black holes—millions to billions of solar masses—reside at the centers of most galaxies, including the Milky Way. Evidence comes from tracking orbital motion of stars in their vicinity, as observed by NASA and ESA facilities, evidence that earned the 2020 Nobel Prize.
Black holes are invisible, but their presence is inferred from accretion disks—hot gas swirling around them emits powerful X-rays—and from gravitational lensing, where their mass bends light from background objects.
Observations by the Event Horizon Telescope (EHT) produced direct images of the shadow of black holes in M87 and Sagittarius A*, confirming Einstein’s predictions about light structure near the event horizon.
Some black holes move at high speeds through space, likely receiving small velocity boosts (often called kicks) from asymmetric supernova explosions or galactic interactions, as detected using Hubble’s precision astrometry.
Black holes also play key roles in cosmic evolution. Tidal disruption events—where a passing star is torn apart—produce luminous flares captured by Hubble and Chandra, providing rare glimpses into black hole activity.
Their immense gravity powers active galactic nuclei and relativistic jets, influencing both their surrounding galaxies and intergalactic environments.
16 April 2021
Light rays from accretion disks around a pair of orbiting supermassive black holes make their way through the warped space-time produced by extreme gravity in this stunning computer visualization. The simulated accretion disks have been given different false color schemes, red for the disk surrounding a 200-million-solar-mass black hole, and blue for the disk surrounding a 100-million-solar-mass black hole. That makes it easier to track the light sources, but the choice also reflects reality. Hotter gas gives off light closer to the blue end of the spectrum and material orbiting smaller black holes experiences stronger gravitational effects that produce higher temperatures. For these masses, both accretion disks would actually emit most of their light in the ultraviolet though. In the video, distorted secondary images of the blue black hole, which show the red black hole's view of its partner, can be found within the tangled skein of the red disk warped by the gravity of the blue black hole in the foreground. Because we're seeing red's view of blue while also seeing blue directly, the images allow us to see both sides of blue at the same time. Red and blue light originating from both black holes can be seen in the innermost ring of light, called the photon ring, near their event horizons. Astronomers expect that in the not-too-distant future they’ll be able to detect gravitational waves, ripples in space-time, produced when two supermassive black holes in a system much like the one simulated here spiral together and merge.