Question: what is the meaning of black hole

Beth Healey answered on 13 Oct 2015:

Good day, this is Adrianos from Greece, I am Beth’s predecessor as a research doctor for the European Space Agency in Antarctica and I am filling in for her today due to connectivity problems over there.

For every star there comes a time when its fuel is exhausted, the star stops emitting light and “dies”. Small and medium stars, like our sun, cool down and become “white dwarfs”, tiny stellar remnants, a shadow of their former selves. But some colossal stars are so massive that they go out with a big explosion rather than smoothly cooling down. This explosion is called a supernova and the reason is that the star crumbles under its own gravity. In such cases, instead of a “white dwarf” star, what is left behind is a “black hole”. The black hole is a spacetime anomaly (this means that we cannot explain it with our knowledge of physics) with huge gravity. It attracts everything around it and its gravitational force is so strong that even light cannot escape it!

Black holes are not totally “evil”, though! They do consume everything around them and grow bigger, but if a star is far enough, it just starts rotating around the black hole, because of the black hole’s gravity. Slowly more and more stars accumulate in orbit, at a safe distance from the black hole. And maybe this is how galaxies come to be: It is believed that there is a supermassive black hole at the heart of every galaxy, like our own Milky Way, but don’t worry, it’s far enough!