Gamma-ray bursts are a threat to life • Hacker News Board

Re: Gamma-ray bursts are a threat to life

#41

Post by nerfhammer » Thu, Jan 29, 2015, 6:18 AM UTC

JumpCrisscross wrote: post #8

> 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 f…

They're not completely sure, but:

> 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

Re: Gamma-ray bursts are a threat to life

#42

Post by cshimmin » Thu, Jan 29, 2015, 6:18 AM UTC

Dylan16807 wrote: post #34

cshimmin wrote: post #33

Earlier quoted context omitted.

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…

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

I was actually basing this argument off of a similar one which gives much shorter windows (like ~1 Myr or something) as an upper bound on the amount of time a civilization can exit, which makes communication with other civilizations even more unlikely. This shorter bound comes from the very pessimistic notion that advanced civilizations will inevitably destroy themselves (e.g. nuclear holocaust). Obviously this one is a somewhat unfounded limit, but one could interpret the Fermi paradox as an empirical basis for the macabre hypothesis >:)

Re: Gamma-ray bursts are a threat to life

#43

Post by analog31 » Thu, Jan 29, 2015, 6:29 AM UTC

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.

Re: Gamma-ray bursts are a threat to life

#44

Post by [deleted] » Thu, Jan 29, 2015, 6:30 AM UTC

cubano wrote: post #15

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,…

[deleted]

Re: Gamma-ray bursts are a threat to life

#45

Post by onion2k » Thu, Jan 29, 2015, 6:33 AM UTC

crystaln wrote: post #29

Is this really an explanation for the Fermi paradox? Would a factor of 0.1 or even 0.01 really change the import of the Fermi paradox?

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

Re: Gamma-ray bursts are a threat to life

#46

Post by austinz » Thu, Jan 29, 2015, 6:38 AM UTC

acadien wrote: post #21

austinz wrote: post #19

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…

Thanks for the paper link! I'll check it out. (The histogram legend seems to indicate two distributions of observed GRBs, the larger centered around 8 degree cones.)

Re: Gamma-ray bursts are a threat to life

#47

Post by lumpypua » Thu, Jan 29, 2015, 6:47 AM UTC

Dylan16807 wrote: post #34

cshimmin wrote: post #33

Earlier quoted context omitted.

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…

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

> The reshuffling of life could even increase the chances of a civilization occurring.

Bumping life out of a local maxima, lol.

Re: Gamma-ray bursts are a threat to life

#48

Post by obstinate » Thu, Jan 29, 2015, 7:01 AM UTC

vorg wrote: post #40

Dylan16807 wrote: post #34

Earlier quoted context omitted.

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

To survive a mass extinction from gamma-ray bursts, a smart species would build a self-sustaining subterranean city with 1 million humans in residence at any one time, perhaps rotating in and out on tours. I'm sure the Chinese will have one within 50 years even if no-one else does. And such subterranean cities are also likely how humans will be living on Mars for thousands of years before it's terraformed.

IIUC Mars will never be terraformed because it is not heavy enough to hold on to atmosphere.

Re: Gamma-ray bursts are a threat to life

#49

Post by firethief » Thu, Jan 29, 2015, 7:32 AM UTC

vorg wrote: post #40

Dylan16807 wrote: post #34

Earlier quoted context omitted.

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

To survive a mass extinction from gamma-ray bursts, a smart species would build a self-sustaining subterranean city with 1 million humans in residence at any one time, perhaps rotating in and out on tours. I'm sure the Chinese will have one within 50 years even if no-one else does. And such subterranean cities are also likely how humans will be living on Mars for thousands of years before it's terraformed.

50 years? We must not allow a mineshaft gap!

Re: Gamma-ray bursts are a threat to life

#50

Post by adrianN » Thu, Jan 29, 2015, 7:48 AM UTC

vorg wrote: post #40

Dylan16807 wrote: post #34

Earlier quoted context omitted.

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

To survive a mass extinction from gamma-ray bursts, a smart species would build a self-sustaining subterranean city with 1 million humans in residence at any one time, perhaps rotating in and out on tours. I'm sure the Chinese will have one within 50 years even if no-one else does. And such subterranean cities are also likely how humans will be living on Mars for thousands of years before it's terraformed.

A subterranean city won't protect your from a GRB.