Scientists studying Einstein’s theory of gravity realized that some massive stars at the end of their lifetimes could undergo a catastrophic collapse! All the matter in the star would be so compressed that that no particle, not even light, could escape from the star’s surface. A remarkable consequence of Einstein's theory was that as the star approached that compressed state, to a distant observer, time on the star’s surface would appear to slow down. The star would appear to “freeze” in its motion, turning redder and redder and fading away. Such stars were originally called frozen stars but since the 1960s we have realized that that such a collapsing star will quickly form what is now called a “black hole” (a region of space from which nothing can escape).
