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Is there a "missing light crisis"?

  1. Dotini

    Dotini 721
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    Currently being reported in the popular press is an interesting-looking missing light crisis. Everybody loves a good mystery, but is it really a mystery, and if so, is there an answer?




    Something is amiss in the Universe. There appears to be an enormous deficit of ultraviolet light in the cosmic budget.

    The vast reaches of empty space between galaxies are bridged by tendrils of hydrogen and helium, which can be used as a precise “light meter.” In a recent study published in The Astrophysical Journal Letters, a team of scientists finds that the light from known populations of galaxies and quasars is not nearly enough to explain observations of intergalactic hydrogen. The difference is a stunning 400 percent.


    “Either our accounting of the light from galaxies and quasars is very far off, or there’s some other major source of ionizing photons that we’ve never recognized,” Kollmeier said. “We are calling this missing light the photon underproduction crisis. But it’s the astronomers who are in crisis—somehow or other, the universe is getting along just fine.”
    Last edited: Jul 10, 2014
  2. jcsd
  3. marcus

    marcus 24,389
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    2014 Award

    Here is the article published in Astrophysical Journal (ApJ) Letters:
    The Photon Underproduction Crisis
    Juna A. Kollmeier, David H. Weinberg, Benjamin D. Oppenheimer, Francesco Haardt, Neal Katz, Romeel A. Davé, Mark Fardal, Piero Madau, Charles Danforth, Amanda B. Ford, Molly S. Peeples, Joseph McEwen
    (Submitted on 10 Apr 2014)
    We examine the statistics of the low-redshift Lyman-alpha forest from smoothed particle hydrodynamic simulations in light of recent improvements in the estimated evolution of the cosmic ultraviolet background (UVB) and recent observations from the Cosmic Origins Spectrograph (COS). We find that the value of the metagalactic photoionization rate required by our simulations to match the observed properties of the low-redshift Lyman-alpha forest is a factor of 5 larger than the value predicted by state-of-the art models for the evolution of this quantity. This mismatch results in the mean flux decrement of the Lyman-alpha forest being underpredicted by at least a factor of 2 (a 10-sigma discrepancy with observations) and a column density distribution of Lyman-alpha forest absorbers systematically and significantly elevated compared to observations over nearly two decades in column density. We examine potential resolutions to this mismatch and find that either conventional sources of ionizing photons (galaxies and quasars) must be significantly elevated relative to current observational estimates or our theoretical understanding of the low-redshift universe is in need of substantial revision.
    6 pages, 3 figures. Submitted to ApJ Letters; 6 pages including 3 figures
  4. marcus

    marcus 24,389
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    It seems like a good occasion to learn more about the "Lyman alpha forest" (let's abbreviate it Laf) wavelengths of light.
    Apparently neutral hydrogen clouds all have individual random motions so the absorption line of this one "Lyman alpha" transition gets randomly doppler shifted all over the place. this one type of absorption, by a lot of different randomly moving clouds, tends to filter out a whole bunch of different lines producing a Laf.

    So the accounting problem is that apparently in nearby intergalactic space more of the H is ionized than they expected, so it filters out less and produces a fainter set of Laf absorption lines---they observe a deficit. so they reason there must be more ionizing UV than their model tells them to expect. Less neutral H than they expected, and fainter Laf lines. That's how I understand it, anyway, on first looking it over.
    Curiously they do not observe a deficit in Laf at higher redshifts!

    So it's as if there is more ionizing (UV) radiation in the universe RECENTLY. So the intergalactic H is more ionized RECENTLY (compared with say 5 billion years ago). If there is more ionizing UV than there used to be, where did it come from?

    at least that might be one direction to go, in searching for an explanation.

    I'm still not sure I understand this. Maybe you understand it better and want to go through and explain.

    Sometimes these mismatches or anomalies observed in some detail or other just go away. They turn out not to stand up under further observation. Or there turns out to be some simple explanation why we should have expected this. etc etc…. I'm not expert and have no sense of whether or not this is to get excited about.

    But it is something to watch. future papers about this will probably CITE this one, so periodically we could check to see if there have been any followups.
    for future reference: http://arxiv.org/cits/1404.2933 (listing the citations to the paper)
    the Inspire database record also will show citations:

    I see there has already been one citation (not by any of the authors of the original,but by some other folks): http://inspirehep.net/record/1292001?ln=en
    It came out later that same month, and tries to think up explanations for the deficit. Abstract looked kind of interesting but I didn't read further.
    Last edited: Jul 10, 2014
    1 person likes this.
  5. Dotini

    Dotini 721
    Gold Member

    Is there a missing photon source crisis?

    At least one science writer has decided to change the headline problem from "missing light" to "missing photon sources". That seems like a step in the right direction. If I had known that yesterday, the title of this thread would change accordingly.

  6. Dotini

    Dotini 721
    Gold Member

    Thanks for your comments and citations, marcus.

    I ran across this recent research article which helped give me some needed perspective on even understanding the problem - let alone any answer to it.


    Journal Reference:
    1. Sebastiano Cantalupo, Fabrizio Arrigoni-Battaia, J. Xavier Prochaska, Joseph F. Hennawi & Piero Madau. A cosmic web filament revealed in Lyman-α emission around a luminous high-redshift quasar. Nature, January 2014
  7. Is there too much of intergalactic hydrogen, too little, or this has nothing to do with the amount of hydrogen?
  8. Dotini

    Dotini 721
    Gold Member

    Last edited: Jul 15, 2014
  9. Jonathan Scott

    Jonathan Scott 1,342
    Gold Member

    Is this effectively just another way of phrasing the well-known fact that there is apparently a sudden drop in the distribution of quasars and active galactic nuclei at low redshift, for which the standard explanation is a strangely uniform universal cut-off in their evolution, and the heretical explanation is that many of those objects have a non-cosmological component to their redshift, causing them to appear further away?
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