Black Hole
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.
Sources
APODs including "Black Hole"
The Supermassive Black Holes of NGC 6240
28 November 2002
The Hubble optical image on the left shows NGC 6240 in the throes of a titanic galaxy - galaxy collision 400 million light-years away. As the cosmic catastrophe plays out, the merging galaxies spew forth distorted tidal tails of stars, gas, and dust and undergo frantic bursts of star formation. Using the orbiting Chandra Observatory's x-ray vision to peer within the bright central regions of NGC 6240 astronomers believe they have uncovered, for the first time, not one but two enormous orbiting black holes, by detecting the characteristic x-ray radiation from the interstellar debris swirling toward them. In the false-color close-up view at right, the x-ray data clearly show the black hole sources (shaded blue) separated by about 3,000 light-years. Einstein's theory of gravity predicts that such a pair of black holes must spiral closer together, and ultimately coalesce into a single, even more massive black hole after several hundred million years. In the final moments the merging supermassive black holes will produce an extremely powerful burst of gravitational radiation.