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Can GRB cause mass-extinctions?

  1. Oct 20, 2005 #1
    This afternoon there will be a colloquium at my university on the topic of GRBs causing mass extinctions. It sounds like a pretty interesting topic and so I want to know what you guys think about it. Here is the offical email that was sent to my FSU account:

    There are two main theories about the sources GRBs. One, which I favor is the hypernovae hypothesis. The other, which this guy probably believes in, is the collision of neutron stars with other neutron stars, or neutron stars with black holes.
     
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  3. Oct 20, 2005 #2

    selfAdjoint

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    I believe there are now thought to be two populations of GRB, short burst below 10 seconds and long ones over that limit. The long bursts have been observed both at the gamma frequency and visually, and the hypernova explanation seems well attested. The short bursts have just been spotted at visual frequencies, and their cause is more speculative.
     
  4. Oct 20, 2005 #3

    SpaceTiger

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    If either type of GRB occurred in our galaxy (and was directed toward us), I think there's little doubt that it would be extremely destructive. I would think it would be hard to determine whether or not it causes mass extinctions, since systems like that are extremely difficult to model the associated remnant would have long since faded. I certainly find it plausible, but wouldn't venture to speculate on whether or not it actually occurred.
     
  5. Oct 20, 2005 #4
    From what I've heard on documentaries, the burst is directed in the direction of the angular momentum of the collapsing star(s), in other words, along the "z" axis. If that is so, then perhaps the fact that we live in a sprial galaxy would make the probabilities greater for star formation with angular moment vectors perpedicular to the galactic plane.
     
  6. Oct 20, 2005 #5
    Not really, an event like a near by GRB, or even an extremely close supernovae, will cause alterations in Earth's isotops via cosmic rays. If a significate alteration in isotops in Earth's crust coincides with a mass extinction then it would support that a GRB or supernovae might have caused it.
     
  7. Oct 20, 2005 #6

    SpaceTiger

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    I was actually referring to the supernova/GRB remnant, but I hadn't thought of that means of verification. Did they say in the talk how easy it would be to distinguish such changes from geological processes? Are the initial isotopic alterations primarily in the atmosphere or crust? Which isotopes in particular are they looking for?
     
  8. Oct 20, 2005 #7

    Garth

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    A problem would be that another major candidate for mass extinctions is an asteroid/comet impact. The signature for those is also anomalous isotope abundancy along the mass extinction line, caused in a similar way by material irradiated by cosmic rays - this time while the impact object was in space.

    It might be difficult to distinguish between the two candidates.

    Garth
     
  9. Oct 20, 2005 #8

    Math Is Hard

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    I'm glad someone posted this. I am working on a biology paper about what high-energy blasts could do to the Earth's atmosphere, and the possibility that one might have caused the late Ordovician extinction. I am reading an article about this in this month's Astronomy magazine, "Do we live in a cosmic shooting gallery?".
    What I don't understand is how it could have been a GRB, since I always thought of them as happening really, really far away (but I am not sure how I got this idea). How probable is it that one could have occurred in our galaxy? I apologize if this is a dumb question.
     
  10. Oct 20, 2005 #9

    russ_watters

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    It is a matter of probability: if there are 10 billion galaxies in our observable universe close enough to notice a GRB and we see 10 of these bursts a year (I think that's about the frequency), the probability of seeing one in any given galaxy (including ours) is 1 in 1 billion per year. So odds would be decent that we'd see one in our galaxy every billion years or so (rough, rough numbers...). Perhaps someone else can help firm up those numbers for your paper...
     
  11. Oct 20, 2005 #10
    Would the statistical highly relevant 62 My extinction cycle of Rohde & Muller have anyting to do with gamma ray bursts? Would it happen about every 62 million years or would the traditional causes (meteorite impacts and trap volcanism) have that typical cycle?
     
  12. Oct 20, 2005 #11

    Math Is Hard

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    Thanks, Russ. I found one source that says we are detecting them at the rate of about one per day.

    In the article I am reading they say that they think GRBs were much more frequent in the early history of our galaxy "when star formation was in full bloom". So I guess the odds of us not getting blasted are a little better than they were? If there's a chance of life forming on planets of other star systems in the Milky Way, the longer interval between the blasts should give them a better shot at it now. I think that's what this article is driving at anyway - that we've missed something in Drake Equation that is pretty influential.
     
  13. Oct 20, 2005 #12

    Astronuc

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    There was a recent gamma ray burst - 27 December 2004 - http://www.everything-science.com/index.php?option=com_content&task=view&id=111&Itemid=2

    The burst came from SGR 1806-20, a neutron star in Sagittarius about 50,000 light years from Earth.

    http://www.nature.com/nature/journal/v434/n7037/full/nature03519.html

    http://en.wikipedia.org/wiki/SGR_1806-20

    from Wikipedia Other sources suggest that 1E 2259+586 is 18,000 ly from Earth.
     
  14. Oct 21, 2005 #13

    Chronos

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    A gamma burst strong enough to trigger mass extinctions would be strong enough to leave a radiation signature in geological formations. Impact events [aka asteroid collisions] would of course pollute these signatures.
     
  15. Oct 21, 2005 #14

    Garth

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    But they may be nearer than we think! (Short GRBs that is)
    Is there a galactic component for the ultra high energy cosmic rays?
    Note: because of the significant energy loss by the GZK (Greisen-Zatsepin-Kuzmin 1966) mechanism, the present universe is not transparent to the highest energy cosmic rays (1020 eV), here.

    Therefore any sources contributing to the bulk of these cosmic rays should be within 500 Mpc of earth for 1019 eV CR particles and a few ten's of Mpc for 1020 eV CR particles.

    A prevalence of 'near-by' merging BHs and Neutron stars?

    Garth
     
    Last edited: Oct 21, 2005
  16. Oct 21, 2005 #15
    I asked the guy giving the colloquium and he told me that it's unlikely that you could look for isotopic anomolies because they would primarily have been in the atmosphere and impossible to desiguish. So I was wrong in saying it would be easy.And he also said GRBs don't necissarily give off lots of cosmic rays, they is one model where they do give off lots of cosmic rays and one model where they don't.

    What would really be the smoking gun would be to find a unusual amount of nitrates in the soil around the time of the mass extinction. Most of the energy from the gamma rays from the GRB would go into turning ozone, molecular oxygen and nitrogen into nitrates. The depletion of ozone would be what would start the extinction. According to his model UVB rays would increase by up to 200% for a decade because of the atmospheric changes. As little as 20% increase in UVB rays will kill plankton.

    That is way off. We see about one burst EVERY DAY. According to his research a "long" GRB would have to be with a few kpc (~6000 light years) to threaten Earth. And according to his estimates there sould have been an average of three GRB in the last billion years this close to Earth. Sorry I can't post the source, I don't think he has a web site.
     
    Last edited: Oct 21, 2005
  17. Oct 21, 2005 #16

    Garth

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    I am being lazy - do you have a breakdown on the frequency of long and short duration GRBs?

    Garth
     
  18. Oct 29, 2005 #17

    Nereid

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    Several things:

    - the 'per galaxy' rate for GRBs (of either type) is still pretty much unknown. The association of long/soft GRBs with (one? type of) supernova is now reasonably well established; however, the frequency of these supernovae is not so well established, nor is the extent to which the 'G's are beamed

    - the association of short/hard GRBs with compact object mergers (NS-NS, NS-BH, BH-BH?) is much more recent (and less secure); that these do 'beam' is, however, reasonably well established

    - whether there are just these two causes of GRBs, of either kind (or, esp, of the 'ones in the middle') is an open question

    - 'starquakes' on magnetars can also produce massive amounts of gammas, though not nearly the flux of even the short/hard GRBs

    - the existence of populations of 'sub-luminous' GRBs is uncertain; if there are significant populations, making estimates of the likelihood of an extinction event on Earth, due to a 'GRB', will be very tough (today)

    - most of the major 'mass extinctions' seem to have more prosaic causes (to do with geophysics rather than astrophysics); the exception is the KT one (a comet/asteroid is clearly implicated); the Cambrian one - who knows? I rather doubt the geological record is good enough (given our present capabilities) to reliably detect a GRB trigger, so attributing a mass extinction to a GRB (or SN or nearby magnetar, or ..) may come down 'finding the shadow' (eliminate all other possible causes, only GRB is left). Here's a good book for those interested: Tony Hallam, Catastrophes And Lesser Calamities: The Causes of Mass Extinctions.

    - and what if mass extinctions are like earthquakes (they follow a power law)?
     
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