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Do new objects ever become visible to us for the first time?

  1. Aug 12, 2013 #1
    Does light from distant objects still continue to reach us "for the first time," or is the universe sufficiently old and its expansion sufficiently fast that this will never again happen? If it does happen, do we have any examples of it? Also, if so, what does it "look like" (i.e. does something just magically seem to all of the sudden appear)?
  2. jcsd
  3. Aug 12, 2013 #2

    Simon Bridge

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    As you look further away, you are looking into the past.
    The analogy here is being in a forest where the trees get younger and younger towards the edges - over time you see the distant trees grow taller and get older, in the far distance sprouts put forth leaves and grow to saplings, and, in the clear ground outside the forest, new sprouts poke their heads up.

    Thus: we get to see new stages in the evolution of the objects that are already there.
    Sometimes this is a slow process, like the accretion of a cloud of dust into a star.
    The ignition of the protostar could be quite quick, particularly in visible light, so that would be the "sudden appearance of a new object" if you like. Similarly a supernova is a very quick event.

    So what it looks like is just the same as the normal changes around us every day.
    What you won't see is fully formed stars or galaxies just popping into visibility - they have to grow into being, like the trees.
  4. Aug 12, 2013 #3
    I was about to ask if we see new "formations" then, but that leaves the question already answered (thinking about the Hubble deep images of "baby" galaxies, and consequently "baby" things within them), gradually of course. Thanks
  5. Aug 12, 2013 #4


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    To affirm what Simon already said, fully formed structures, like galaxies, never suddenly pop into view. This is the inference often drawn from talk of there being galaxies in the universe whose light has not yet had time to reach us. What they fail to mention is light emanated by their precursor structures will reach us long before that of the mature galaxy.
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