Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

'First Light' and the Universe's early years

  1. Oct 21, 2005 #1

    DaveC426913

    User Avatar
    Gold Member

    I've just returned from a University Cosmology lecture that introduced a phenomenon called 'First Light'. It appears to be coming from Hubble observations over the last 5-10 years (so, very recent). I have never heard of such a theory.

    The theory says that the Big Bang created all the H and He in the universe in the first three minutes, which then floated around in gaseous form for hundreds of thousands of years.

    Now, apparently, gaseous hydrogen does not clump into masses on galactic scales, which means the galxies could not have been formed from this initial state. In other words, we could not get here from there.

    The only way hydrogen can clump on that scale is in a plasmic state (protons stripped of their electrons). When a plasma, H clumps nicely at that scale.

    So, something happened, somewhere in the first billion years of the universe's life. Some form of energy swept across the universe, converting all the H from gas to plasma. This also turned the universe opaque, since plasma transmits light poorly. This is corroborated by the very deep space observance of some sort of opaque shell at the 12.5Gy distance.

    In this plasmic state, the H was able to clump on galactic scales, subsequently converting back to gaseous state again, and leaving a universe the way we see it now.


    Has anyone heard of such a thing?
     
  2. jcsd
  3. Oct 22, 2005 #2
  4. Oct 22, 2005 #3

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Dave,
    I think you are just a little confused.

    First light refers to the epoch of first stars that form in the universe.

    After the initial brilliance of the Big Bang the universe would have gradually cooled off and become dark, even at the surface of last scattering (of the CMB) the universe would have only been glowing dimly in the deep red end of the spectrum. The wavelength of peak emission would have been about 10,000 Angstroms in the infra-red. This period is called the 'Dark Ages'.

    We infer that there must have been an initial population of probably very massive stars at an early period 20<z<10 called Population III stars. There was a lot of early re-ionisation in the cosmic medium and a lot of early high metallicity only produced in stars. The appearance of such PopIII stars is called 'First Light'.

    There is a problem explaining how galaxies form, after the epoch of last scattering of the CMB as the Jean's mass is about 106MSolar possibly the mass of a large PopIII but not a galaxy, but before that epoch the Jean's mass would have been 1018MSolar, the size of a galactic cluster.

    Here non-interacting Dark Matter is brought in to rescue the situation, it can begin to collapse before the epoch of last scattering, when the cosmic medium was still ionised and form gravitational wells into which the ordinary matter can fall. The process is modelled numerically and can be seen here amongst other web sites.

    I hope this helps.

    Garth
     
  5. Oct 22, 2005 #4

    DaveC426913

    User Avatar
    Gold Member

    No, I am not confused. This was the lecture.

    He did talk about very massive popIII stars, and speculated that their exotic novae might have been the cause of this wave of energy, but pointed out that they simply do not know what caused it.
     
  6. Oct 22, 2005 #5

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yeah, it's not certain that Pop III stars are the dominant cause of reionization. The other potential contributor that gets a lot of attention is quasars, since we expect them to have been forming very rapidly during that epoch.

    There's actually a bit of confusion in the astro community about the issue of reionization (this wave of energy), because we have two separate observations telling us that it should have occurred at different times. Analysis of WMAP data implies a very high redshift for reionization (~15), while observations of quasars in SDSS indicate a lot of neutral gas at z ~ 6. This may not actually be a conflict, since there's nothing that says reionization can't happen twice, but it certainly lends itself to less elegant theories.
     
  7. Oct 22, 2005 #6

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Perhaps two separate events? i.e. PopIII stars were the first objects to form, and being massive had very short lives, going 'hyper-nova' at z ~ 15, and then quasars forming from the BHs left behind finally firing up prior to z ~ 6?

    Just a suggestion.

    Garth
     
  8. Oct 22, 2005 #7

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This is what I meant by:

     
  9. Oct 23, 2005 #8

    Garth

    User Avatar
    Science Advisor
    Gold Member

    I'm glad we agree - so the task in hand is to determine the distribution and Initial Mass Function of the Pop III stars that will deliver the observed distribution of early high metallicity and re-ionization?

    How does the total baryon density and initial metallicity required to produce this IMF compare with that determined from the cosmological model?

    Garth
     
  10. Oct 23, 2005 #9

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Models of Pop III stars are too crude to make this comparison as of yet. Aside from the IMF (which is extremely difficult to predict, even locally), one also has to consider star formation efficiency and feedback effects. There's a lot of research going on in this area right now, but we're a long way from constraining cosmology with it.
     
  11. Oct 23, 2005 #10

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Thank you ST.

    What are the problems in the formation of stars with zero metallicity? Is it that they require rotation as well as very large masses?

    Garth
     
  12. Oct 23, 2005 #11

    First off, I don't think an absolute (Void) (Edge) of space has ever been detected by Astronomers, Star systems are being found no matter how far we look out into the Universe, The better our telescopes become the more we find. (Deep Star Fields)

    It's quite possible that the Universe always existed changing from one state to another eternally.

    Maybe one day, When Telescopes become powerful enough we will find another Universe far far away from our own. But it would be incredably far away and very very dim, current Telescopes would not be powerful enough to detect a second Universe trillions and trillions of light years away.

    But for now it is the (known) Universe that sets the limits to it size and edge.

    We need better eyes in the sky.

    Maybe when we link array some telescopes on the Moon with Earth base Telescopes we can collect enough light to prove the Universe has no real edge. It may even take a linked Telescope array the size of our Solar System.

    I hoped that I helped.:smile:
     
  13. Oct 23, 2005 #12
    Yes, and the farther back we look, the more galaxies and quasars we find, generally with super-solar metallicities and masses equivalent to or often larger than that of the galaxies in our own neighborhood.

    Indeed, although if you wish to explore an infinite steady state universe, the adherents of the Standard Model will scoff and call you names. If you dare to explore the possibility that the universe did not begin 13.7Gy ago in a Big Bang, you will find yourself in a rather lonely endeavor.

    By definition, our universe contains all that exists, and our visible universe contains all that we can possibly observe from our vantage point. There is a limit to how much we can see. That limit may be shown to us as we observe more and more distant objects that are redshifted into the infrared and ultimately into the CMB. Olber's Paradox does not seem to be much of a problem if EM from distant objects are redshifted into lower and lower frequencies. If you look at the night sky at the appropriate frequencies, the sky is brightly and pretty uniformly illuminated.
     
    Last edited by a moderator: Oct 23, 2005
  14. Oct 23, 2005 #13

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The problems that I'm aware of include the fragmentation of the initial molecular cloud (important for determining the IMF), mass loss due to stellar winds/rotation and, of course, the subsequent supernovae. Note that it also depends on the environment in which the stars are forming. A strong UV flux can ionize the gas in protogalaxies and prevent star formation, while a strong X-ray flux can increase the rate of molecular hydrogen formation and actually induce star formation. There's much literature on the subject and I'm most certainly not doing it justice. If I get the time, I'll try to find a nice review paper and put it in the Classic Papers sticky.
     
  15. Oct 23, 2005 #14

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    He's referring to the fact that we observe an extremely high column density of neutral hydrogen gas at redshifts ~6. Neutral hydrogen has a nasty habit of absorbing the light we use to observe galaxies and quasars, so effectively blocks off the very distant universe from our view.


    Our telescopes are limited by brightness, not distance, so it's not necessarily true that star systems are being observed as far as we're theoretically capable of observing. The brightness you would expect at a certain distance depends on your cosmological model. There is certainly a maximum redshift at which stars/galaxies have been observed so far (~6.5), but it's still unclear as to whether that will become a long-term boundary.


    I don't think we could ever rule out the possibility that the universe simply shifted from one state to another at some point in the past. It's more of a philosophical point than a scientific one.

    Not really, the universe is only of order 10 billion years old, so we can't see light from objects more distant than about 10 billion light years. There are some caveats to this, but none of them involve observations of stars or galaxies at the distances you're describing.
     
  16. Oct 24, 2005 #15

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Thank you ST. I'll look forward to that.

    At the recent monthly meeting of the Royal Astronomical Society we had a lecture by Dr Danny Lennon -The Magellanic Clouds: Laboratories for understanding Massive Stars. He made the point in passing that it was very difficult to understand how very massive stars - referring to Pop III - could form without rotation.

    I would like to understand how that worked as it seemed counter-intuitive.

    Garth
     
  17. Oct 24, 2005 #16
    what do we mean when we say the Universe has an age?

    I have been wondering about the idea that the universe has an age. Given the space-time deformations of special and general relativity, isn't it true that the universe, whatever that is, must have different ages for different observers? Since there is no preferred referance frame, shouldn't we be careful to state what reference frame we are using? But then I suppose we could just assume we are talking about the reference frame common to observers here on Earth in the 21st century.

    And yet, we are talking after all about cosmological events at the horizon of our powers of observation, regions where acceleration is significant. Even closer to home, in the black hole now thought to be at the center of our own galaxy, regions near the event horizon must experience time quite differently from the rate we consider ordinary.

    I am sure participants in this forum have considered these things. Is there an unspoken consensus?

    Thanks,

    Richard
     
  18. Oct 24, 2005 #17

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It is indeed possible for that to be the case, but when homogeneity and isotropy are assumed (and/or observed), then the universe can be defined to have a single age.


    I'm implicitly referring to a reference frame stationary relative to the microwave background and yes, you're right that such a specification needs to be made for the age to be well defined. The earth is not, actually, stationary relative to this frame.


    The consensus is as I gave above, but it really is just a matter of convention. This particular convention is by far the most convenient for doing cosmology, but you could consider an infinite number of reference frames in calculating the age of the universe for a particular observer. The reason we don't bother is that such frames tell us nothing more about cosmology, they only rescale what we already know...and in a messier way, because they will be observer-specific.
     
  19. Oct 24, 2005 #18

    turbo

    User Avatar
    Gold Member

    Even that has to be taken as a bit of a generalization. Every observer has his or her own "present" and resides at a time cusp such that wherever we look we are receiving information from the past. For instance, as we look out into space, we see farther and farther back in time in every direction. This is because our observations of distant objects is limited by the time observational information (in EM) takes to get from there to here. This effect is not limited to astronomical observations. If you could build a high enough tower in Minnesota and I could build one in Maine (to see each other around the curvature of the Earth), and I waved "hi" you would not see me waving in your present, but as I appeared 1/186 of a second in your past. This is because it's about 1000 miles (OOM guess here) between us and the visual information takes a finite amount of time to get from me to you. If you could wave back as soon as you saw me wave (REALLY good reflexes), I wouldn't see your acknowledging wave until 1/93 sec after I waved. That's close enough to "simultaneous" for practical purposes, but it should demonstrate that we each reside at our own personal "present".
     
    Last edited: Oct 24, 2005
  20. Oct 24, 2005 #19
    Thanks for the answers.
    R
     
  21. Oct 25, 2005 #20

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Previous posts pretty much answer the question. Every observer has a personal clock that measures the 'age' of the universe. If you run the movie 'observable universe' in reverse, it 'shrinks' to zero size after a finite amount of time. However, not many few theorists believe it physically reaches such a state, just that existing theories fall apart right around the time the size of the universe appoaches the planck scale. You have a similar situation when black holes form. They collapse until they almost, but not quite, become singularities... at least by our clock.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: 'First Light' and the Universe's early years
  1. The early universe (Replies: 22)

  2. The early universe (Replies: 1)

Loading...