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B Question About The Stars -- Can they have died before we see their light?

  1. Jun 21, 2017 #1
    Stars have always interested me, I view them every night with my telescope. One thing really interested me though, if star's light can take thousands of years to reach our planet. I was wondering, does this mean that the light we see could be the light of a star that has died, maybe for hundreds of years?
     
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  3. Jun 21, 2017 #2

    Borg

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    Yes and we would find out when the light reaches us.
     
  4. Jun 21, 2017 #3
    Yes, however, every star you can see now is still there. Space is so huge that almost every visible star is actually fairly close to us, and we can determine where they are in their life cycles. Most are middle aged and we know that they'll continue to live for billions of years. As far as I know, the only star that you can see with the naked eye that might not be there anymore is Betelgeuse, and that's still very unlikely. Most estimates give it at least another hundred thousand years or so to live and it's only 700 light years away.

    We'll actually know it's exploded a couple of hours before we actually see the light from the explosion. When the core collapses, it creates a blast of neutrinos and gamma radiation. The gamma radiation heats up the outer layers of the star and causes the explosion, but it takes time for that energy to trudge through the millions of miles of dense plasma to escape. The neutrinos, on the other hand, went straight through the plasma like it wasn't even there and gets a head start on the faster photons, so they make it here first.
     
  5. Jun 21, 2017 #4

    Drakkith

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    Remember that the OP has a telescope. :wink:

    Indeed. I can't decide if I want to see Betelgeuse go supernova in my lifetime or not. It would be an absolutely stunning sight, but at the same time I really like the Orion constellation. :cry:
     
  6. Jun 21, 2017 #5

    Chronos

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    We see dead stars on a regular basis with large telescopes like the HST. The Hubble deep field image [HDF] includes numerous galaxies out to a redshift of z=6 or more. Galaxies at redshift z=6 are believed to be sources of photons that were emitted around 12 billion years ago, much older than the life expectancy of an average size star like the sun. Such stars would have long ago used up their original fuel reserves and are now faint corpses. Of course bright stars, the easiest ones to detect at great distances, are more massive and have much shorter life spans than the sun, so they too are long gone. In short, most of the stars comprising galaxies in the Hubble deep field are no longer emitting detectable photons. If we could see them as they are today, the HDF galaxies would look significantly different than at present. Cosmologists use images of galaxies at different redshifts to formulate models of how stars and galaxies have evolved over the history of the universe.
     
  7. Jun 21, 2017 #6

    Vanadium 50

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    Eta Carinae has been visible to the naked eye in historical times and it is not unreasonable to think it has already gone supernova.
     
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