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Space Earth

Linking Mass Extinctions To the Sun's Journey In the Milky Way 199

schwit1 writes "In a paper published today on the Los Alamos astro-ph preprint service, astronomers propose that as many as eleven past extinction events can be linked to the Sun's passage through the spiral arms of the Milky Way. (You can download the paper here [pdf].) From the paper: 'A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy's various spiral arms.'"
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Linking Mass Extinctions To the Sun's Journey In the Milky Way

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  • Oort cloud? (Score:5, Interesting)

    by Anonymous Coward on Saturday September 21, 2013 @03:45PM (#44913065)
    I only read the abstract, but while it proposes a correlation it did not speculate on the exact cause of the extinction. I wonder if passing 'nearer' (I use the term loosely) to higher concentrations of stars might disturb the Oort cloud, sending more comets than normal careening in towards the inner solar system ... or if we might catch stragglers from other stars' own Oort Clouds.
    • Re:Oort cloud? (Score:5, Interesting)

      by icebike ( 68054 ) on Saturday September 21, 2013 @04:18PM (#44913223)

      That is how I read it, or simply wandering comets, asteroids, broken free of what ever they were orbiting. Even interstellar dust concentrations perturbing our own asteroids might be enough.

      But I was more surprised to learn the Sun was not traveling in rough unison with a (relatively) fixed spiral arm. Is this normal for all stars?
      If all stars are wandering why do spiral arms exist at all? Why wouldn't the Milky Way simply be a disk?

      • Re:Oort cloud? (Score:4, Interesting)

        by TapeCutter ( 624760 ) on Saturday September 21, 2013 @04:25PM (#44913253) Journal
        Spiral arms are shock waves. The stars themselves don't move with the wave, they are created by it.
        • Re:Oort cloud? (Score:4, Insightful)

          by icebike ( 68054 ) on Saturday September 21, 2013 @04:38PM (#44913333)

          Ah, such clarity.

          Have you told those clowns at Harvard [harvard.edu] about this?

          • The Harvard article in no way contradicts what TapeCutter said. Please clarify your point.

            • Re:Oort cloud? (Score:5, Interesting)

              by icebike ( 68054 ) on Saturday September 21, 2013 @06:18PM (#44913857)

              “We find they are forming spiral arms,” explains D’Onghia. “Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.”

              No mention of Shock waves, or even a hint of what might cause such shock, or how such shock could be transmitted in the vacuum of space.

              Density waves, (shock waves) another term for Stochastic Star Formation theory, is no longer the leading theory of the existence of spiral arms. Its not the 1960s any more.

              This shock wave theory suggest that stars are relatively uniformly distributed, even in the inter-arm gaps, but because of density waves inducing star birth at their leading edge and star death at their trailing edge, the arms simply appear brighter.
              Hubble pretty much put that theory to bed. see http://en.wikipedia.org/wiki/NGC_1300 [wikipedia.org] The inter-arm gaps are real.

              Further the so called shock wave theory (Stochastic Star Formation) postulates that stars on average do not actually leave their "arm", and the visual effect of the arm at any give place pretty much spans the life of a star. (born on the leading edge, dead by the trailing edge). Yet this story suggests the Sun has wandered through the arm(s) several times.

              Further, even when perturbations from a passing galaxy might have triggered them via gravity, the arms persist. and in some galaxies even after
              the perturbations disappear. So what is driving these? What would cause "shock waves"?

              The 60's are calling, and they want their theory back.

              • Re:Oort cloud? (Score:5, Informative)

                by dkf ( 304284 ) <donal.k.fellows@manchester.ac.uk> on Saturday September 21, 2013 @07:14PM (#44914173) Homepage

                No mention of Shock waves, or even a hint of what might cause such shock, or how such shock could be transmitted in the vacuum of space.

                Via the interstellar medium [wikipedia.org], of course. It's pretty tenuous, but most certainly is capable of sustaining phenomena like shock waves. Which isn't to say that that's necessarily the particular process that is dominant in the galactic arms; it could also be something relating to magnetism, as the physics of a flowing magnetically-coupled medium is viciously difficult to work with (i.e., highly non-linear). And I've got no idea what happens at the phase change boundaries between the parts of the ISM which are plasmas and the parts which are conventional (tenuous) gasses; phase changes can do "interesting" things.

                As for what's powering it all, you've got some exceptionally powerful energy sources out there. Black holes in particular can pump vast amounts of energy into the surrounding volume of space. The stellar wind from very high mass stars would be another interesting source.

      • Re:Oort cloud? (Score:4, Interesting)

        by wulfhere ( 94308 ) <slashdot&huffmans,org> on Saturday September 21, 2013 @04:29PM (#44913281)

        Man, do I wish for mod points. I was thinking the exact same thing about our star wandering. If the spiral arms are hostile to life, that could *significantly* cut down on the number of stars capable of supporting life.

        • Mass extinction events are not hostile to life. They may in fact be essential to evolution.
        • by dryeo ( 100693 ) on Saturday September 21, 2013 @10:39PM (#44915159)

          A good chunk of the galaxy is hostile to life. The galactic core and areas of extreme star formation for example. Both due to radiation, hot blue gigantic stars put out a lot of radiation and then go supernova and the stars are close enough that the odds of a close enough encounter to perturb a planets orbit go up. A large star may perturb the Earths orbit from a light year, or as others mentioned, trigger more objects falling in from the Oort cloud or such.
          Many stars also have non-circular orbits that take them through the core periodically.

    • Re:Oort cloud? (Score:4, Informative)

      by symbolset ( 646467 ) * on Saturday September 21, 2013 @04:27PM (#44913275) Journal

      In the paper this is diiscussed as one possible explanation.

      Such encounters would not pose a di- rect hazard to life on Earth by changing the orbit of the Earth around the Sun, but could pose a haz- ard by disturbing the Oort Cloud

  • Intergalactic space (Score:4, Interesting)

    by Dan East ( 318230 ) on Saturday September 21, 2013 @03:55PM (#44913107) Homepage Journal

    Assume it were possible to slingshot our sun out of the galaxy into intergalactic space. Would we be better off there, or does the Milky Way offer some sort of protection against whatever's out there (radiation, etc)?

    • by AlphaWolf_HK ( 692722 ) on Saturday September 21, 2013 @04:09PM (#44913183)

      The reapers hide in intergalactic space, so we're probably not safe there.

    • by Teancum ( 67324 )

      It could be worse.... we could simply be falling into the galactic core and passing within a few light years of the central galactic black hole every few million years. Instead, the orbit of the Sun is roughly circular and stays in the main galactic disk.

      The other possibility is that the Earth could fly into intergalactic space and the Sun could go in a different direction. That would make things very comfortable.

    • by wjcofkc ( 964165 )
      An interesting thought. I suggest you read The Black Destroyer by A. E. van Vogt.
    • by symbolset ( 646467 ) * on Saturday September 21, 2013 @05:09PM (#44913489) Journal
      It is possible for the Sun to be flung out of the galaxy by passing too close to a much larger star. Stars are flung out of galaxies quite frequently in much the same way that asteroids and comets are frequently flung out of the solar system. The Earth would be unlikely to survive such an event. But if it did, no, there is nothing out there between galaxies that is more harmful than whirling through this relatively dense dust and grit.
  • So if we are moving through spiral arms, and it appears our neighbouring stars appear 'relatively' fixed to our position does this mean that all stars in our galaxy move through the spiral arms? Do the spiral arms move w/respect to all the stars like some sorta density wave?
    • Pretty much, yeah.
    • by icebike ( 68054 )

      That was also my question.

      Is this movement along the plane of the galaxy's disk, or oscillating above and below the disk? How sure are we that there even are spiral arms? If there were arms, then why would be be traveling through them, instead of with them? Why would an orbiting star system travel faster than other star systems in its proximity, and still remain in the same orbit?

      • Re:spiral arms? (Score:4, Informative)

        by bill_mcgonigle ( 4333 ) * on Saturday September 21, 2013 @06:26PM (#44913889) Homepage Journal

        Yeah, it wasn't clear from TFS or TFA what they were talking about, but further down in the discussion:

        TL;DR: the Sun orbits the galaxy faster than the spiral arms, and when the solar system passes through gas clouds in the spiral arms, that can send more Ort-cloud comets at the Earth.

        The motion of the spiral arms around the cen-
        tre of the Galaxy is somewhat slower than that of the
        stars that make up the galaxy, which means that, as
        the Sun orbits the centre of the Galaxy, it follows
        a path that takes it through the spiral arms every
        few tens of millions of years. In the spiral arm envi-
        ronment, the Solar System is exposed to a far more
        hazardous and busy regime than in the inter-arm re-
        gions (our current location). The Earth could be
        relatively close to a star when its life comes to an
        end in a supernova explosion { which could certainly
        pose problems for life, although such supernovae are
        relatively rare, and the odds of the Earth being suf-
        ciently close to one for life to be exterminated en-
        tirely are low, even within a spiral arm (Beech 2011).
        At the same time, close encounters between the Sun
        and neighbouring stars become more frequent, as do
        encounters between the Sun and giant gas clouds
        (see Fig. 2). Such encounters would not pose a di-
        rect hazard to life on Earth by changing the orbit
        of the Earth around the Sun, but could pose a haz-
        ard by disturbing the Oort Cloud (Porto de Mello et
        al. 2009), a vast cloud of comets (Oort 1950) which
        stretches to a distance of at least 100 000 AU from
        the Sun. The Oort Cloud is thought to contain tril-
        lions of cometary nuclei, left over from the formation
        of the Solar system, which are only tenuously grav-
        itationally bound to the Sun (the outer members of
        the cloud are around halfway to the nearest star).
        An encounter with a passing star or distant molec-
        ular cloud can be enough to deflect an Oort cloud
        comet, throwing it onto a new orbit that will bring
        it into the inner Solar system { where it can pose a
        threat to the Earth. The closer the star approaches
        to the Sun, or the more massive it is (or both), the
        more comets it will scatter inwards, and therefore
        the more likely it will be that one of those in-falling
        comets will hit the Earth.

    • Re:spiral arms? (Score:5, Interesting)

      by richard.cs ( 1062366 ) on Saturday September 21, 2013 @05:28PM (#44913591) Homepage

      Do the spiral arms move w/respect to all the stars like some sorta density wave?

      That's exactly what the spiral arms are, they can't be the same stars orbiting together in that shape as that would imply a rigid body rotation. The situation where everything moves around together as if it were nailed to a rigid cosmic disc doesn't work because the orbit time of the stars at the centre of the galaxy is less than that of the stars at the edge. This is a consequence of the orbital physics, it's essentially the only way the forces can balance.

      So, the stars in the centre whiz around quickly (in cosmological time anyway) whilst the ones at the edge take forever. The spirals are simply areas of higher star density but they are not the same stars all the time. This region does rotate but more slowly than the stars contained within it. So, why are there areas of increased star density? No-one's entirely sure but it seems likely that these are actually regions with higher rates of star formation, with many young, short-lived blue stars.

  • by Anonymous Coward on Saturday September 21, 2013 @04:26PM (#44913267)

    Before you read too much into this report, remember that a preprint service makes papers available to researchers in the field before the paper has undergone the peer-review process. This allows the results to be circulated amongst other researchers quickly as the peer-review process can takes quite some time.

    While not as bad as say having a press conference about discovering "Cold Fusion" before any peer-review only to find that the results could not be duplicated, take the papers contents with a grain of salt as the research has not been peer-reviewed.

    You might think of it like the answers you get in the back of a textbook that have usually been done by an author's grad students. Most of them are probably correct, but nobody has gone over them with a fine-tooth comb to verify their correctness.

    • Yes. Go look at some of the other titles. TFA is one of the more approachable ones . Your head will aslpode.

      "Inflationary Instabilities of Einstein-Aether Cosmology "
      "Simulation of homologous and cannibalistic CMEs produced by the emergence of a twisted flux rope into the Corona"
      "ORIGAMI: Delineating Cosmic Structures with Phase-Space Folds"
      "X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars"

      and of course, my favorite:

      "The peculiar Raychaudhuri equation"

  • by Misagon ( 1135 ) on Saturday September 21, 2013 @04:29PM (#44913287)

    There has previously been a theory that these mass reoccurring extinctions would have been created by the near passing of a hypothetical star that we would have been unable to detect because it would be on the other side of the Oort cloud.
    I suppose that this new finding will debunk that theory for good.

    The hypothetical star had been named Nemesis [wikipedia.org]. I know of it only because I ready about it in a novel by Asimov [wikipedia.org] recently.

  • by ebcdic ( 39948 ) on Saturday September 21, 2013 @04:49PM (#44913377)

    ... is when we pass through the next one!

  • By Sir Arthur Conan Doyle

    http://en.wikipedia.org/wiki/The_Poison_Belt [wikipedia.org]

  • by Omega Hacker ( 6676 ) <omega@omega[ ]net ['cs.' in gap]> on Saturday September 21, 2013 @05:33PM (#44913621)

    I've got a novel by John Brunner written in 1982 called The Crucible of Time (), which documents a (very non-human) species through its scientific awakening. Throughout the book they're discovering that their planet is getting closer to a cloud of debris dense enough to massively devastate the surface, possibly shatter the planet. In the end they manage to build enough arks to save the species. The foreward reads:

    "It is becoming more and more widely accepted that the Ice Ages coincide with the passage of the Solar System through the spiral arms of our galaxy. ..."

  • A competing hypothesis [centauri-dreams.org] tries to show a correlation between mass extinctions and the times when our solar system is farthest to the "north" of the galactic disk. I've always found that hypothesis tantalizing and somehow compelling even though it cannot explain the KT event. Presumably there can be more than one cause of mass extinctions.

  • Linking Mass Extinctions To the Sun's Journey In the Milky Way

    I just went and tried to read the research. I couldn't understand a word of it, but it probably means the Earth is going to be consumed in a fiery cataclysm.

    Just my luck this would happen when the Bears are 2-0 and my fantasy team is in first place. Well, I guess it's time to run up the credit cards.

    • by Z00L00K ( 682162 )

      Essentially it comes down to statistics - there's more junk floating around in the center of the spiral arm than at the edges so more risk of hitting something on the way through. Or having an asteroid or comet disturbed by a passing item.

      In general meteorites hitting Earth have a speed of about 11 to 15 km/s, but that's only applicable for those that follows basically the same trajectory as Earth. If you meet something extrasolar then the speed can be a lot higher, which means that a smaller rock can cause

      • In general meteorites hitting Earth have a speed of about 11 to 15 km/s, but that's only applicable for those that follows basically the same trajectory as Earth. If you meet something extrasolar then the speed can be a lot higher, which means that a smaller rock can cause great effects and still not be traced as an impact causing an extinction event due to insufficient evidence.

        So what you're saying is I shouldn't run up the credit cards, and the Bears are gonna win the Super Bowl? Thanks!

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