• Question: If nothing travels at the speed of light, except light, how can a black hole also pull light into itself?

    Asked by waveicle to Adam, Rob, Sheila, Suzie on 23 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 23 Mar 2011:

      Speed isn’t really a factor in this point – it’s more a case of the huge gravitational effect it has on space time – if it can bend the path of light into it, it can’t escape.

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 23 Mar 2011:

      The black hole doesn’t need to be travelling at the speed of light – in fact usually they aren’t travelling at all I think. The fact that light gets trapped is because of the huge force of gravity near the black hole, which is so strong that nothing can escape even if it is travelling at the speed of light. So the only thing happening really is the force of gravity… But we have to go a bit further than Newton’s laws and into Einstein’s general relativity to understand why light (which has no mass) can get trapped by gravity. It’s because the actual space-time itself gets curved… and this affects light as well..
      Did you know we’ve observed the bending of light be seeing the light from distant stars get bent around the sun? They figured it out during a solar eclipse quite a long time ago by comparing the distance between the stars that they saw during the solar eclipse to the distance they saw at night when the sun wasn’t around – and it was different! It was the first real test of general relativity I think…

    • Photo: Robert Simpson

      Robert Simpson answered on 23 Mar 2011:

      Light cannot escape from a black hole because of the immense gravity. The escape speed to get out of the black would have to be higher than the speed of light no nothing escapes.

    • Photo: Sheila Kanani

      Sheila Kanani answered on 23 Mar 2011:

      The gravity in a black hole is so strong that light travels into it and just can’t escape!

Comments

  • Photo: waveicle

    waveicle commented on :

    @Everyone, thnaks! but as Robert mentioned that “the escape velocity to get out of the black would have to be higher than the speed of light”, doesnt it mean that the speed of gravitiotional pull is greater than the speed of light and if so, how FAST is it? and how it can be measured?

    @Suzie, great explanation!

    • Photo: Suzie

      Suzie commented on :

      thanks waveicle! I don’t think we can ascribe a speed to gravitational pull… this is where the analogy used by Brian Cox in wonders of the universe breaks down (where he shows a river going over a waterfall and explains that at some point he won’t be able to swim fast enough to avoid going over the edge!). But unfortunately I don’t have a better explanation…