Is the gamma-ray burst a spherical field, or is it a narrow, directed cone? If the latter, I wonder how the burst spreads/diffuses as it travels and what sort of equation governs the energy flux with respect to distance and initial conditions.
Great question! Since they're emanated in jets, the GRBs travel in a conical shape that spreads out as it travels. Check out page 19 of this paper, it has a histogram of the jet opening angle;
http://arxiv.org/pdf/1101.2458.pdf
Then you can figure out the flux from the area of a circle on a sphere, which is something like
2πr^2(1−cosθ)
Where theta is the opening angle and r is the distance from point of emanation of the GRB.
I think there are multiple types of GRBs and some can be spherical. Two that I have read about are neutron stars colliding and large solar mass > 100 exploding and leaving no remnant. I've read that these types of bursts can blow the atmosphere off of a planet. http://en.wikipedia.org/wiki/Hypernova
Does anybody know if a gamma-ray burst is preceded by an increased neutrino flux? I've heard that neutrinos will actually arrive at earth several hours before the light from a supernova. When the core of a star collapses, the light is physically prevented from coming outwards until the collapse is complete. Since the neutrinos move right through the gas, they are emitted as soon as the explosion occurs. Would detecting neutrinos be sufficient to give up ~4 hours of warning before a gamma-ray burst?
Neutrino detection in correlation with GRBs is problematic at best, because the events tend to be so far away and neutrino emissions are not expected to be focused into cones the same way EM and charged particles are, by virtue of not interacting with electromagnetic processes they'll be emitted in all directions. (There is some hypothetical neutrino/antineutrino emission within the GRB cone, but it's likely a weak signal and hasn't been measured in practice.)
We expect GRB neutrino flux to weaken far below the detection threshold by the time it gets here. Across these vast distances, neutrinos should also lag behind photons because they're not technically as fast as light.
The other question is what would we do with that advance warning if it existed? We can't do anything about the fact that our atmosphere is going to absorb these gamma rays, and chances are the event wouldn't be energetic enough to kill us directly as we're walking around so there is no point in taking cover either. The damage to our ecosystem is going to be what kills us, not radiation exposure.
It is complicated by the fact that this implies intelligent civilizations have a very finite window of opportunity in order to communicate. 500 Myr is a pretty short on cosmic timescale; so the odds that:
1) our civilization comes to exist in some 500Myr window
2) another civilization comes to exist in another 500Myr window
3) Signals sent from that other civilization arrive at the right time for ours to observe them
are considerably lower than just the odds that two civilizations develop that are advanced enough to communicate with each other.
It's possible that gamma bursts are an example of a "great filter" - an event the stops life that Fermi Paradox and Drake equation can't really account for: http://en.m.wikipedia.org/wiki/Great_Filter
Probably not. Implicitly, the Fermi paradox looks at life in our own galaxy, which has apparently been quite lucky overall cosmologically. Many galaxies out there are hostile to life (GRBs are just one factor, I would argue that being a metal-poor galaxy with no active star formation is an even worse problem for life), but that doesn't have any bearing on life in our own galaxy - of which we have a sample size of one.
That said, even the friendly corners of the universe aren't a pony farm. It's more than likely for any given planet to find itself staring down the barrel of a stellar particle accelerator at some point during its time. Earth probably did, too, and we're still here. Whether it's a complete sterilization event depends on the amount of energy deposited. Depleting the ozone layer isn't enough. A planet would have to be pretty close to the event in order to get annihilated completely, so glancing blows with some limited impact on the ecosystem are probably more common in our cosmic neighborhood.
> The authors found previously that GRBs are more frequent in low-mass galaxies such as the Small Magellanic Cloud with a small fraction of elements heavier than hydrogen and helium. This reduces the GRB hazard in the Milky Way by a factor of 10 compared with the overall rate.
Smaller galaxies are deadlier, got it. Is this because GRBs tend to emanate from the galactic centre? And larger galaxies, having more stars further from the centre, have more "habitable" space? Or does it have to do with the higher frequency of heavy elements in large galaxies? If the latter, how do heavy element concentrations cause or moderate GRB activity?
> There are at least two different types of progenitors (sources) of GRBs: one responsible for the long-duration, soft-spectrum bursts and one (or possibly more) responsible for short-duration, hard-spectrum bursts. The progenitors of long GRBs are believed to be massive, low-metallicity stars exploding due to the collapse of their cores. The progenitors of short GRBs are still unknown but mergers of neutron stars is probably the most popular model as of 2007.
I am not an expert, but my understanding is that long GRBs are expected as the result of the collapse of very massive stars. These stars are short lived (few million years) and very luminous. Metals (in astrophysics anything heavier than Helium) in the envelope of such a massive star would drive strong radiation-pressure driven mass losses (because of the increased opacity). Only very metal poor stars are able to remain sufficiently compact and massive at the onset of collapse to be able to trigger a GRB.
If the Universe is too dangerous for life to exist elsewhere, what are the chances that it's not too dangerous to exist here? Not very high.
Either there is an abundance of life out there, or we are most likely just experiencing a brief period of lucky safety in a tiny corner of the Universe.
Probably not. <JeffGoldblum> Life will find a way! </JeffGoldblum>
> The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments2, 3, 4, 5. Remarkably, these fragments are readily reassembled into a functional 3.28-megabase genome. Here we describe the relevant two-stage DNA repair process... figure [1]
Direct radiation exposure is not the only threatening aspect of a GRB and even Deinococcus Radiodurans can't withstand the full onslaught of a nearby GRB [2], but I do believe that D.R. is a good enough proof of concept to argue that adaptation is not only feasible but probable. GRBs would set life back a few hundred million years (whether here or in a remote galaxy), but I doubt they would put an end to it.
Certainly seems like one of them, if this claim is true: "The Milky Way would therefore be among only 10% of all galaxies in the universe – the larger ones – that can sustain complex life in the long-term."
Here the trick is that a planet-scale barrier is needed, since we need to defend against tipping our ecosystem into chaos. If we're Type II, then we could theoretically just let the earth get whacked and restart using nearby systems to seed it. Kinda funny how a disaster stops being as terrible once you have backups:
Type 0: extinction
Type 1: mega-scale engineering effort to block GRB
I wonder if 500 million years is long enough for an intelligent civilization to come up with some sort of early warning system such as figuring out which stars might be turning dangerous. The article doesn't say how long the bursts last.
The burst lasts as long as it takes the stuff (radiation) get past the planet. That is only a few seconds. That radiation is travelling at light speed so given our present knowledge an early warning system is unthinkable. However for a star big enough to go supernova, expected life expectancy and spectral analysis can give you some estimate rounded to the 10s or 100s of millions of years.
So, assuming we don't also all die of burns or cancer or natural disasters caused by the sudden influx of energy into the atmosphere immediately...
According to http://www.epa.gov/ozonedesignations/faq.htm , ground ozone tends to be produced by pollutants, i.e. we are ourselves producing this ozone, mostly by burning fossil fuels.
So we have actually already produced at least 10% of the ozone we'd need to repopulate the upper atmosphere, we're just producing it in the wrong place...
From reading these links, it sounds like ground-level ozone is often a seasonal effect, so it could well be that a lot of this ozone is being produced on a regular basis and then dissipates in some fashion.
So... my back of the envelope calculation would be that yes, if we had unlimited funding and a bit of time, we should be able to produce enough ozone just by burning organic matter. The key question would be, can we get that ozone in the right place?
With unlimited funding, and with a deliberate effort to burn fossil fuels at high altitudes, my gut feeling would be yes... I think the key question would be would we be able to do this in time, before we all burn to a crisp along with most of the plant and animal life on Earth...
Let's assume this happened tomorrow, and it took another 500 million for life to evolve to what we would consider intelligent. Would anything of our civilisation be left? What would be the best way to leave a record that we existed?
Just keep going business as usual. Given that we have plenty of trilobite fossils from the Cambrian, might even expect future paleontologists to find some fossilized skulls.
I think we might be earth's last chance at an advanced civilization. We've depleted all of the readily available energy sources necessary for an emerging civilization (easily-accessible fossil fuels). It will take at least 500 million years for them to be replenished. And in one billion years, the increased luminosity from the sun will wipe out most advanced life due to runaway greenhouse effects. So there's a pretty narrow window in-between.
We could launch 10,000 time capsules into space on trajectories that bring one of them back to Earth every 50,000 years or so. They would have to be designed in a way that makes re-entry spectacularly visible so they would be noticed and it would be possible to track them down. Not perfect, but at least there is some chance that one would arrive while an intelligent species is thriving.
This makes a lot of assumptions about extra-terrestrial life. This article assumes that all "life" depends on a protective ozone layer and that it's similar to life on Earth.
The article doesn't assume that all life depends on a protective ozone layer. The article states several times that life like that on earth depends on a protective ozone layer.
As I read New Cosmogony by Stanislaw Lem, I cannot help but think that older civilizations (gods), hated organic life very much and tried to erase it everywhere.
I know I may get dinged for this observation, but it is something that really bothers me about certain types of forecasts...be it weather or things of this sort...
That would be the "50% forecast", which, when examined with a bit of thought, really is saying "well, maybe it did, and maybe it didn't...we don't really know but hey, doesn't 50% sound scientific!"
For sure, GRBs are scary, potentially life-wiping events, but, really..don't we deserve better than a coin-flip?
It's just statistics. You look at how often we see GRBs, how long they last (on average), how intense they are (on average) then do a big time integral and figure out the odds of a big one hitting earth over such and such a period of time. There is no better than a coin-flip, the coin flip is the odds of it having happened (by the author's approximations). If I can help explain any further please let me know.
[+] [-] austinz|11 years ago|reply
[+] [-] acadien|11 years ago|reply
Then you can figure out the flux from the area of a circle on a sphere, which is something like 2πr^2(1−cosθ) Where theta is the opening angle and r is the distance from point of emanation of the GRB.
[+] [-] gmoes|11 years ago|reply
[+] [-] pixl97|11 years ago|reply
https://en.wikipedia.org/wiki/Gamma-ray_burst#Energetics_and...
[+] [-] neaanopri|11 years ago|reply
[+] [-] Udo|11 years ago|reply
We expect GRB neutrino flux to weaken far below the detection threshold by the time it gets here. Across these vast distances, neutrinos should also lag behind photons because they're not technically as fast as light.
The other question is what would we do with that advance warning if it existed? We can't do anything about the fact that our atmosphere is going to absorb these gamma rays, and chances are the event wouldn't be energetic enough to kill us directly as we're walking around so there is no point in taking cover either. The damage to our ecosystem is going to be what kills us, not radiation exposure.
[+] [-] crystaln|11 years ago|reply
[+] [-] cshimmin|11 years ago|reply
1) our civilization comes to exist in some 500Myr window
2) another civilization comes to exist in another 500Myr window
3) Signals sent from that other civilization arrive at the right time for ours to observe them
are considerably lower than just the odds that two civilizations develop that are advanced enough to communicate with each other.
[+] [-] onion2k|11 years ago|reply
[+] [-] Udo|11 years ago|reply
That said, even the friendly corners of the universe aren't a pony farm. It's more than likely for any given planet to find itself staring down the barrel of a stellar particle accelerator at some point during its time. Earth probably did, too, and we're still here. Whether it's a complete sterilization event depends on the amount of energy deposited. Depleting the ozone layer isn't enough. A planet would have to be pretty close to the event in order to get annihilated completely, so glancing blows with some limited impact on the ecosystem are probably more common in our cosmic neighborhood.
[+] [-] nerfhammer|11 years ago|reply
http://www.nature.com/scitable/blog/postcards-from-the-unive...
http://arxiv.org/abs/astro-ph/9901322
[+] [-] edgarvm|11 years ago|reply
[+] [-] JumpCrisscross|11 years ago|reply
Smaller galaxies are deadlier, got it. Is this because GRBs tend to emanate from the galactic centre? And larger galaxies, having more stars further from the centre, have more "habitable" space? Or does it have to do with the higher frequency of heavy elements in large galaxies? If the latter, how do heavy element concentrations cause or moderate GRB activity?
[+] [-] nerfhammer|11 years ago|reply
> There are at least two different types of progenitors (sources) of GRBs: one responsible for the long-duration, soft-spectrum bursts and one (or possibly more) responsible for short-duration, hard-spectrum bursts. The progenitors of long GRBs are believed to be massive, low-metallicity stars exploding due to the collapse of their cores. The progenitors of short GRBs are still unknown but mergers of neutron stars is probably the most popular model as of 2007.
http://en.wikipedia.org/wiki/Gamma-ray_burst_progenitors
[+] [-] dsqrt|11 years ago|reply
[+] [-] JonnieCache|11 years ago|reply
[+] [-] theoh|11 years ago|reply
[+] [-] crystaln|11 years ago|reply
Either there is an abundance of life out there, or we are most likely just experiencing a brief period of lucky safety in a tiny corner of the Universe.
[+] [-] cLeEOGPw|11 years ago|reply
I don't get it why so many people either want life to be basically on every second star or not exist outside Earth at all.
Let's just accept that Fermi and all others hugely overestimated the chances and roll with it, will be far more productive imo.
So with the GRBs in mind, we can safely narrow livable space to outskirts of Milky Way and focus our search there.
[+] [-] tectonic|11 years ago|reply
[+] [-] jjoonathan|11 years ago|reply
> The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments2, 3, 4, 5. Remarkably, these fragments are readily reassembled into a functional 3.28-megabase genome. Here we describe the relevant two-stage DNA repair process... figure [1]
Direct radiation exposure is not the only threatening aspect of a GRB and even Deinococcus Radiodurans can't withstand the full onslaught of a nearby GRB [2], but I do believe that D.R. is a good enough proof of concept to argue that adaptation is not only feasible but probable. GRBs would set life back a few hundred million years (whether here or in a remote galaxy), but I doubt they would put an end to it.
[1] http://www.nature.com/nature/journal/v443/n7111/fig_tab/natu...
[2] http://www.world-science.net/exclusives/070226_grb-life.htm
[+] [-] benbreen|11 years ago|reply
[+] [-] e0m|11 years ago|reply
http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_ext...
It stripped the Earth's ozone and killed all the surface-dwelling organisms.
[+] [-] jchrisa|11 years ago|reply
[+] [-] HCIdivision17|11 years ago|reply
Here the trick is that a planet-scale barrier is needed, since we need to defend against tipping our ecosystem into chaos. If we're Type II, then we could theoretically just let the earth get whacked and restart using nearby systems to seed it. Kinda funny how a disaster stops being as terrible once you have backups:
Type 0: extinction
Type 1: mega-scale engineering effort to block GRB
Type 2: start over from scratch easily
[0] http://en.wikipedia.org/wiki/Kardashev_scale#Theoretical_exa...
[+] [-] johnchristopher|11 years ago|reply
[+] [-] analog31|11 years ago|reply
[+] [-] has2k1|11 years ago|reply
[+] [-] JulianMorrison|11 years ago|reply
[+] [-] swombat|11 years ago|reply
According to http://www.epa.gov/ozonedesignations/faq.htm , ground ozone tends to be produced by pollutants, i.e. we are ourselves producing this ozone, mostly by burning fossil fuels.
From http://www.ozonelayer.noaa.gov/science/basics.htm , we find that 90% of that is in the upper layer, so 10% is lower layers.
So we have actually already produced at least 10% of the ozone we'd need to repopulate the upper atmosphere, we're just producing it in the wrong place...
From reading these links, it sounds like ground-level ozone is often a seasonal effect, so it could well be that a lot of this ozone is being produced on a regular basis and then dissipates in some fashion.
So... my back of the envelope calculation would be that yes, if we had unlimited funding and a bit of time, we should be able to produce enough ozone just by burning organic matter. The key question would be, can we get that ozone in the right place?
With unlimited funding, and with a deliberate effort to burn fossil fuels at high altitudes, my gut feeling would be yes... I think the key question would be would we be able to do this in time, before we all burn to a crisp along with most of the plant and animal life on Earth...
[+] [-] lucaspiller|11 years ago|reply
[+] [-] pacala|11 years ago|reply
http://www.fossilmuseum.net/Paleobiology/CambrianFossils.htm
[+] [-] sshumaker|11 years ago|reply
[+] [-] mc808|11 years ago|reply
[+] [-] sneak|11 years ago|reply
[+] [-] lxe|11 years ago|reply
[+] [-] colordrops|11 years ago|reply
[+] [-] thesz|11 years ago|reply
[+] [-] unknown|11 years ago|reply
[deleted]
[+] [-] cubano|11 years ago|reply
That would be the "50% forecast", which, when examined with a bit of thought, really is saying "well, maybe it did, and maybe it didn't...we don't really know but hey, doesn't 50% sound scientific!"
For sure, GRBs are scary, potentially life-wiping events, but, really..don't we deserve better than a coin-flip?
[+] [-] acadien|11 years ago|reply
[+] [-] unknown|11 years ago|reply
[deleted]
[+] [-] dcre|11 years ago|reply
[+] [-] deft0nes|11 years ago|reply
[+] [-] jcoffland|11 years ago|reply