black hole

A black hole is a collapsed star. When high-mass stars use up all their fuel, their cores collapse inward. The heaviest collapsed star cores become black holes. The pull of its gravity is so strong that nothing nearby—dust, stars, even light—can escape. Black holes are still one of the most mysterious objects in space.

First candidate: Cygnus X-1
When observed: early 1970s
Types: star-sized, supermassive, and mini
Quantity: dozens known, billions possible
Origin: star-sized—where massive stars have died; supermassive—in center of galaxies; mini—created by the Big Bang
Significance: Gravity is so strong in a black hole that nothing can escape.

Image credits: main image: Accretion Disk Binary System Drawing Credit, courtesy of STScI and NASA The Center of Centaurus, courtesy of E.J. Schreier (STScI) et al.,and NASA; quote, © AMNH/Frank Summers.