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Can we tell when a Star has died the moment it happens?

  1. Aug 24, 2013 #1
    Light just now reaching us from Andromeda Galaxy was created literally millions of years ago, around 2.5 to be in the ballpark.

    When you look at a star, you're literally looking at the past.

    That means tonight, when we look up, The light that lets us see Andromeda was created when the genus Homo first appeared here on Earth.

    Is it possible that Andromenda, or any other star for that matter, could be dead and gone, but we don't know about it because the light hasn't traveled far enough yet?

    Like for example, if Andromeda just suddenly died today, would we know about it? Or would we not find out until 2.5 million years from now and suddenly realize we can't see it anymore

    Hopefully I'm phrasing my question correctly.
  2. jcsd
  3. Aug 24, 2013 #2


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    Gold Member

    Yes we only see the light that was emitted 2.5 million years ago, if andromeda or anyother star went supernova today we won't know until enough time has past for that light to reach us. The time in years is the same as the number of light years away the object is. Even for our own Sun the light is 8 minutes old by the time we see it here on earth.
  4. Aug 24, 2013 #3
    Trollcast basically summed it up. Even when our Sun becomes a red giant, we will not be able to tell until about 8 minutes after the actual event. But at the point we find it out. We will all be killed so it really wont matter.
  5. Aug 24, 2013 #4
    Ah, that's what I figured. Thanks for clearing that up.
  6. Aug 24, 2013 #5


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    Staff: Mentor

    Well... to be clear, becoming a red giant is a continual process that takes thousands to millions of years once it's started, not an event that just suddenly happens.

    But yes, it takes 8 minutes for any changes in the sun to reach us.
  7. Sep 12, 2013 #6


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    Staff: Mentor

    I remember reading a very short SciFi story about a mage who told his emperor he discovered how to make a star disappear. Emperor pointed to some star and asked the mage to do his trick. And the mage did, but the star was still twinkling...

    If memory serves me well story didn't end up good for the mage. Emperor had some disappearing tricks ready too, and because of the much smaller distance their effects were visible instantly.
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