• Question: How does a black hole give off light?

    Asked by Mason The Amazing :) to Andrew, Hina, Ian, Kathryn, Leah-Nani, Xu on 14 Jun 2018.
    • Photo: Kathryn Burrows

      Kathryn Burrows answered on 14 Jun 2018:

      I assume that by light you mean Hawking radiation. This is hard to explain and I am not sure I really get it yet. Black holes do not give off light as such, any light shone on a black hole will never be reflected and return. No light which passes the event horizon (the edge of a black hole) can return. Hawking radiation is an effect in which a process known as quantum vacuum fluctuations cause a matter-antimatter particle pair to be formed, one falls into the black hole and the other flies away. In this way it appears as if the black hole is giving away radiation. This was proposed by Stephen Hawking but I do not believe has ever been experimentally observed.

    • Photo: Leah-Nani Alconcel

      Leah-Nani Alconcel answered on 15 Jun 2018:

      If you’re wondering how they’re observed, it’s by how the bend the light from the things around them, rather than by giving off light themselves.

    • Photo: Andrew Margetts-Kelly

      Andrew Margetts-Kelly answered on 19 Jun 2018:

      It’s open to debate. There are a couple of theories (Hawking radiation, Lepton evaporation was once theorised, black body emission from a hot event horizon), but none are to date have been testable. The inability to test these theories is because to the outside observer it takes an infinite amount of time for anything to reach the event horizon, and so it takes a very very long time for for any emission from near the event horizon to escape.It’s one of those things we might never know for sure.

Comments

  • Photo: Kathryn

    Kathryn commented on :

    When I wrote my answer I forgot about X-ray waves radiating from the location of black holes! In this case the Xrays do not come out of the black hole itself, but from dust clouds being consumed by the black hole. As the black hole pulls the dust cloud inside, it heats it up quite alot and this gives off X-ray radiation.