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"
M82's Middle Mass Black Hole
14 September 2000
Black holes are probably the most bizarre creatures in the modern astronomical zoo. And after years of pondering black holes as either stellar mass objects seen in binary star systems or enormous supermassive black holes at the centers of galaxies, astronomers now have strong evidence for another exotic species -- middle mass black holes. The leading candidate for the ultradense middle ground is indicated in this false-color detail of a sharp x-ray picture from the space-based Chandra Observatory. A close-up of x-ray sources near the center of starburst galaxy M82, the cropped Chandra image spans about 4,000 light-years. M82 itself is around 11 million light-years distant. The arrowed source has recently been convincingly demonstrated to exhibit x-ray characteristics of an object whose gravitational field holds more than 500 times the mass of the sun within a volume the size of the moon! Astronomers also note that unlike the supermassive variety which are thought to lie at the centers of galaxies, this middle mass black hole is about 600 light-years from the center of M82. Theories for the formation of a middle mass black hole include the collapse of a "hyperstar" formed by the coalescence of many normal stars, or the direct merger of stellar mass black holes.