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"
Short Gamma-Ray Bursts Localized
17 October 2005
What causes gamma-ray bursts? The most energetic type of explosions known in the cosmos has been an enigma since discovered over 30 years ago. It now appears that there may not be one unique type of progenitor. Long duration gamma-ray bursts (GRBs) have been localized, over the past few years, to blue regions in the universe rich in star formation. Massive young stars nearing the end of their short lives commonly explode in these regions. Astronomers associate these long duration GRBs, that can last from seconds to minutes, with a type of stellar explosion common in young massive stars. Over the past few months, short duration GRBs have finally been localized and found to occur in different types of regions -- not only blue regions rich in star formation. Many astronomers therefore now theorize that short GRBs, which typically last less than one second, are the result of a different progenitor process than long GRBs. A leading model is that a short GRB will occur when a neutron star either impacts another neutron star or a black hole. Such collisions may occur well after star-forming regions have otherwise burned out. Pictured in the above illustration, two energized neutrons stars finally approach each other in their orbits, a death spiral that might end with a short GRB.