Black Holes
Regions of spacetime where gravity is so extreme that nothing, not even light, can escape.
🌟 Formation
Stellar black holes form when massive stars (above ~20 solar masses) exhaust their fuel and collapse. The core implodes in a supernova explosion, leaving a black hole behind. Supermassive black holes (millions to billions of solar masses) inhabit the centers of most large galaxies; their formation is still debated.
🔵 Event Horizon
The boundary beyond which nothing can return. Not a physical surface, just a point of no return. The Schwarzschild radius defines its size: r = 2GM/c2. For an Earth-mass black hole, this would be about 9mm. For the Sun, about 3km.
🌀 Singularity
At the center, general relativity predicts infinite density and zero volume: a singularity. Most physicists believe a future theory of quantum gravity will replace this with something finite. We literally cannot describe what happens at the center with current physics.
🌡️ Hawking Radiation
Stephen Hawking predicted in 1974 that black holes slowly evaporate by emitting thermal radiation due to quantum effects near the event horizon. The smaller the black hole, the faster it evaporates. A stellar black hole would take longer than the current age of the universe to evaporate.
📸 First Images
The Event Horizon Telescope captured the first image of a black hole shadow in 2019: M87* at 6.5 billion solar masses, 55 million light-years away. In 2022, they imaged Sagittarius A*, the black hole at the center of our own Milky Way galaxy, at 4 million solar masses.
🔗 Gravitational Waves
LIGO first detected gravitational waves from two merging black holes in 2015, confirming a prediction from general relativity made 100 years earlier. The collision released more energy in a fraction of a second than all the stars in the observable universe combined.