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"
A Galactic Cloud of Antimatter Credit:
1 May 1997
The center of our Milky Way Galaxy is full of surprises. Its latest spectacular is a mysterious cloud glowing in gamma rays produced by annihilating antimatter particles! Star Trek fans are all too familiar with the consequences of mixing matter (electrons) and antimatter (positrons) - the particles catastrophically annihilate converting their masses to energy according to Einstein's famous E=mc2. Positron/electron annihilation energy is emitted as gamma rays with photon energies of 511,000 electron volts. Searching for these high energy photons, the OSSE instrument onboard NASA's orbiting Compton Gamma Ray Observatory has recently produced this map of the Galactic Center (GC) region. As anticipated, it shows annihilation gamma rays as a bright spot at the GC with fainter horizontal emission from the galactic plane. Astoundingly, it also reveals a large and unexpected cloud of annihilation radiation, probably about 4,000 light years across, extending nearly 3,500 light years above the GC. What could have created this cloud? Associated with no previously known object, it seems to imply that a fountain of antimatter positrons streams from the GC. Present guesses about the source of the positrons include the violent and exotic environments surrounding starbirth, neutron star collisions, and black holes at the GC. Are there other such clouds in our Galaxy?