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.'"
Oort cloud? (Score:5, Interesting)
Intergalactic space (Score:4, Interesting)
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)?
Re:Oort cloud? (Score:5, Interesting)
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)
Re:Oort cloud? (Score:4, Interesting)
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.
Nemesis: Debunked theory (Score:5, Interesting)
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.
Re:Intergalactic space (Score:5, Interesting)
Comment removed (Score:5, Interesting)
Re:spiral arms? (Score:5, Interesting)
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.
Not exactly a new concept (Score:5, Interesting)
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. ..."
Re:Rubish (Score:5, Interesting)
If you want to see what I'm talking about, just search the science sites about it.
Yes, it is an intriguing idea, but No, it doesn't hold up to scrutiny.
Re:Oort cloud? (Score:5, Interesting)
“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.