Black holes trap all light, making them invisible. Yet, astronomers detect and measure them through effects on nearby matter, radiation, and spacetime.
BulletsIn
- Black holes invisible, no light escapes event horizon
- Gas, dust spiral in, form hot accretion disc, emit strong radiation
- Bright emissions allow detection billions of light years away
- Star motions near galaxy centres reveal black hole mass
- Faster orbiting stars = heavier black hole
- Velocity dispersion used for precise size estimates
- Reverberation mapping tracks light delays from accretion disc
- X-ray telescopes detect intense glow from falling matter
- Motion of nearby stars proved Sagittarius A in Milky Way
- Gravitational waves from collisions reveal merging black holes




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