• Question: How do black holes suck things towards them?

    Asked by peter296 to Simon, Ollie, Brian on 28 Apr 2020.
    • Photo: Simon Spichak

      Simon Spichak answered on 28 Apr 2020:

      Hi Peter! Imagine we have a very, very soft mattress. Any time you place something heavy on that mattress, it forms a small dent. Now the universe is kind of like a much more complex version of this mattress. The mattress here represents spacetime – it’s the plane on which everything in our wonderful universe sits. Since spacetime is like our very soft mattress, if we place something with lots of mass, it begins to curve inwards. Now because a black hole has an extremely high density and mass, it curves spacetime way down! Just imagine getting a bowling ball, squeezing it to the size of a grain of sand and dropping it onto the mattress! https://qph.fs.quoracdn.net/main-qimg-427ed922546bf0b7dd36c77b8b15cdac-c That graphic is pretty useful – basically anything with any sort of mass does curve spacetime, like anything would curve our super soft mattress. But the heavier the object – the larger the curve.

      Now because we have this extreme curvature in space time, anything that approaches this region is sucked in by this curvature. It’s kind of like dropping some marbles onto a ramp – they are sucked downward by the curvature of our ramp much the same way that things are pulled in by the black hole. It’s a very weird aspect of our very weird universe!

    • Photo: Ollie Otter

      Ollie Otter answered on 28 Apr 2020:

      Hi Peter 296,

      Black holes don’t actually suck things towards them but instead they ‘fall’ towards it. Any object in space with mass will also have gravity and bends the space around itself. Think of it as a metal ball that lies on top of a taut membrane, it will create a dip in said membrane. Now if we put a smaller metal ball on the same membrane it will fall towards the bigger metal ball. Something similar is happening in space.
      Black holes are the heaviest objects compacted in a very small piece of space, so the bending of space around it is so strong that it will create a very deep ‘dip’ in space and anything that will come close to the black hole will fall towards it. The gravity around it is so strong that even light falls towards it and cannot escape anymore. That’s why it’s called a black hole, because no light can shine from it