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"
Our Galaxy's Magnetic Center
19 June 2019
What's the magnetic field like in the center of our Milky Way Galaxy? To help find out, NASA's SOFIA -- an observatory flying in a modified 747 -- imaged the central region with an instrument known as HAWC+. HAWC+ maps magnetism by observing polarized infrared light emitted by elongated dust grains rotating in alignment with the local magnetic field. Now at our Milky Way's center is a supermassive black hole with a hobby of absorbing gas from stars it has recently destroyed. Our galaxy's black hole, though, is relatively quiet compared to the absorption rate of the central black holes in active galaxies. The featured image gives a clue as to why -- a surrounding magnetic field may either channel gas into the black hole -- which lights up its exterior, or forces gas into an accretion-disk holding pattern, causing it to be less active -- at least temporarily. Inspection of the featured image -- appearing perhaps like a surreal mashup of impasto art and gravitational astrophysics -- brings out this telling clue by detailing the magnetic field in and around a dusty ring surrounding Sagittarius A*, the black hole in our Milky Way's center.