What are Black Holes? (Astronomy)

Stars do not last forever. After a star has burned all its fuel, gravity collapses the remaining matter together. For very large stars, a Black Hole is formed. This is an object so dense that anything that gets too close will completely disappear from view, including light. 1:03 History of Black Holes 1:49 Einstein’s theories of relativity 3:12 Are black holes real? 3:48 Finding black holes 4:13 Binary Stars 4:54 Schwarzschild Radius and the Event Horizon 5:24 Finding the mass of a black hole 5: