• Question: How can a Black hole suck everything into it even light?!!

    Asked by ttmadman2000 to Cesar, Emily, Jamie, Kate, Philippa on 15 Jun 2011.
    • Photo: Jamie Gallagher

      Jamie Gallagher answered on 15 Jun 2011:

      Hi tt,

      Well because our planet is large it has a gravitational pull- so things fall to the earth. The black holes have so much mass in such a small area that the gravity is encridibly strong. So strong nothing can escape- it sucks everything into it including light. Maybe Cesar can shed more light on the mystery

    • Photo: Cesar Lopez-Monsalvo

      Cesar Lopez-Monsalvo answered on 15 Jun 2011:

      This is a good one. A black hole does not suck everything into it, it only happens if you are really close. For example, if suddenly the entire earth was compressed to the size of a marble, the moon will remain orbiting around the planet (actually, around the centre of mass of the two, see my answer about gravity http://ias.im/47.62 ) just as if nothing would have happened to the earth. Of course for the things living on its surface, it would be very unpleasant!! The gravitational attraction acting on your feet would be significantly stronger than in your head, and you will be spaghettified (we do use this word)!! This would really happen! Now let me tell you what a black hole actually is.

      A black hole is a consequence of Einstein’s theory of relativity. This theory, as I have explained in other answers, is a geometric theory of gravity (see here http://ias.im/47.305 and here http://ias.im/47.195). Part of the job of a theoretical physicists is to find out and interpret the results of our mathematical theories of nature. Black holes are simply one of them and they were “mathematically discovered” almost immediately after Einstein completed his theory. In this “mathematical” sense, a black hole divides spacetime into two regions, inside (where the centre of the black hole is) and outside (where the rest of the universe is). A “boundary” separates the two regions. This is a one way only boundary which we call the “horizon”. One way of understanding it, is that once you cross it, the centre of the black hole is no longer a “place in space”, but “an event in your future”!!! Since not even light can escape its own future, then it cannot longer avoid the centre of the black hole.

      Finally, this may have leave you with the impression that this objects are purely mathematical stuff. That is not the case. In fact, you can easily find out which objects will eventually become black holes. We have also found many black holes around, in particular the super-massive one in the centre of our galaxy around which many stars orbit. I will try to find a video made out of images taken over the last 20 years of many stars orbiting this gigantic black hole.