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What is the event horizon?

  1. May 2, 2012 #1

    I've heard a fair bit about the event horizon of a black hole. What exactly is the event horizon?

  2. jcsd
  3. May 2, 2012 #2


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    It is the point where the escape velocity equals the speed of light. It not a physical thing, but marks the boundary of "no return" . Anything that passes closer to the black hole than its event horizon, can never do anything but fall in closer to the black hole, this includes light.
  4. May 2, 2012 #3
  5. May 7, 2012 #4
    The mothers of all event horizons!


    Astronomers Find the Most Supermassive Black Holes Yet
    by Amy Shira Teitel on December 7, 2011

    Each of these black holes has an event horizon — the point of no return where nothing, not even light can escape their gravity — 200 times larger than the orbit of Earth (or five times the orbit of Pluto). That’s a mind-boggling 29,929,600,000 kilometres or 18,597,391,235 miles.

    Beyond the event horizon, each has a gravitational influence that extends over 4,000 light years in every direction.
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