• Question: How can light be sucked into a black hole through gravity, because I didn't think it was an object, I thought it was just a state of where we are in comparison to where the sun is?

    Asked by maddiet to Mark, Matthew, Mike, Paul, Sabina on 13 Mar 2014.
    • Photo: Sabina Hatch

      Sabina Hatch answered on 13 Mar 2014:


      As I understand it, only objects with mass are are pulled toward the black hole because of its very dense mass (that gives it exceptional gravitational force). But we see things because of reflection, light bouncing off an object and coming to our eye. However with a black hole all the light is absorbed, none of it is reflected – so it looks like empty black space. It doesn’t actually pull light towards it, because light has no mass. But objects that have mass and produce light (i.e. stars) will be pulled towards it.

    • Photo: Paul Coxon

      Paul Coxon answered on 13 Mar 2014:


      This is a really incisive question, the nature of black holes is a very active field in physics today. There are many debates about how they work and why they should even exist at all!

      Light doesn’t really get ‘sucked’ into a black hole like in a vacuum cleaner. Light is being trapped in there because the mass of the black hole is so high, the gravitational field it creates around itself is extremely strong. It’s so strong it causes the fabric of space to warp and change shape .

      Imagine space to be flat like a trampoline, now place a heavy object like a bowling ball in the middle. The mass of the ball pulls the trampoline down making a deep pit. If you tried rolling across the trampoline, it’d naturally roll towards the heavy bowling ball.

      The same happens in space with a black hole. The mass of the black hole bends space by such a high amount that even a ray of light, (which is moving very fast) if it travels close enough, gets bent and absorbed inside.

      We see things around us by collecting the light which gets scattered off objects into our eyes. If no scattering occurs, we can’t see anything. This is why a black hole is said to be ‘black’ – because all light is trapped and none can reflect off it. It’s simply a region of ‘nothingness’.

    • Photo: Mark Jackson

      Mark Jackson answered on 16 Mar 2014:


      Light can indeed be sucked into a black hole – in fact that is precisely why they are called black, because anything (even light) closer than a certain distance away will be sucked in. It’s not so much whether something is an ‘object,’ but that black holes distort space and time. Anything – object or not – will have to move in this curved spacetime, and light (like anything else) will fall in if it gets too close. This is one of the main differences between modern gravity – described by Einstein’s Theory of General Relativity – and the old Newtonian framework. This difference was used to prove that Einstein’s theory was correct, as I describe at http://goo.gl/SMdVJt

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