
Gamma-ray bursts are a threat to life - curtis
http://cerncourier.com/cws/article/cern/59937
======
austinz
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.

~~~
acadien
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](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.

~~~
jbert
Do you know if there is any bias to the orientation of the jets?

e.g. in a spiral galaxy, do they tend to align with the axis of rotation and
so do less damage locally (spray out "up and down" from the galaxy)?

~~~
jjaredsimpson
jets are randomly oriented with no preferred orientation.

------
neaanopri
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?

~~~
Udo
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.

~~~
hanoz
How useful a barrier is the earth itself for the initial burst? Would there be
any benefit in arranging to be on the opposite side of it for the duration?

~~~
Udo
If it's an exceptionally strong burst, yes. If it's not (which is very
likely), there is no need.

------
crystaln
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?

~~~
cshimmin
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.

~~~
Dylan16807
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.

~~~
vorg
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.

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

~~~
Sophistifunk
Why not, if the extinction mechanism is disruption of the ozone layer?

~~~
knodi123
Well, my understanding could be wrong, but it seemed like the risk is to the
ecosystem, not to human bodies directly. We personally don't need to be
protected from the burst itself.

------
JumpCrisscross
> _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?

~~~
nerfhammer
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](http://en.wikipedia.org/wiki/Gamma-
ray_burst_progenitors)

------
JonnieCache
Greg Egan's fantastic _Disaspora_ begins with a GRB hitting earth. It isn't
pretty. Hence the title. Best scifi I've ever read.

~~~
theoh
Actually the title is "Diaspora"... Nothing to do with disasters.

~~~
JonnieCache
Admittedly I did make a typo there but the diaspora is motivated/necessitated
by the disaster.

~~~
Udo
It's an interesting typo, also because disaster literally means "bad star".

~~~
atlantic
And the etymology of dis-aster is astrological: a negative event caused by an
unfavourable planetary configuration, by "bad stars".

------
crystaln
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.

~~~
cLeEOGPw
Or life is rare and can be found here and there.

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.

~~~
HCIdivision17
I think it's generally because the balance point isn't a stable equillibrium.
There's no force that encourages balance - it would have to be serendipitous.
That's unlike the extremes, where a thriving interstellar civilization likely
leads to mass colonization or that life is hard and typically goes extinct
before then.

The time scales in these sorts of estimates are enormous, often tens or
hundreds of times the span we needed to rise up. So if we even have an inkling
to be expansionary (and we do), and aliens are like us in wanting to thrive
comfortably (with enough space per unit being), then it's likely they too
would have at least a mild drive to expand. Over mnay millions of years, even
a very mild push out would fill a galaxy.

------
tectonic
Is this the Great Filter?

~~~
benbreen
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."

~~~
fiatmoney
Actually, filters that select on galaxy scale are unlikely to be _the_ "great
filter", because we don't seem to see any artificially generated signals
coming from within our own galaxy. This particular filter does strike within
our own galaxy though, just to a lesser degree.

So maybe.

~~~
api
It seems like it might exclude a lot of the galaxy, the central part, from
hosting long lived complex life.

This would mean that complex life is more common along the outer rim, where we
are. This in turn means that the median distance between complex living
biospheres might be very large, further reducing the likelihood of visitation
or receiving signals.

~~~
jerf
There's a reasonably broad consensus that life isn't possible in the central
part of the galaxy due to _normal_ excessive radiation levels, even before
considering extreme events.

Of course, galactic size being what it is, these two "central parts" could
have boundaries differing by, oh, say, twenty thousand light years no problem.

I forget the details but I've seen arguments that too far away from the core
is bad too.

------
e0m
There is a hypothesis that the Ordovician–Silurian mass extinction 450 million
years ago was caused by a Gamma-ray burst!

[http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_ext...](http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events#Gamma_ray_burst_hypothesis)

It stripped the Earth's ozone and killed all the surface-dwelling organisms.

------
jchrisa
How far along the Kardashev scale do we need to before we can build a shield?

~~~
HCIdivision17
At least Type I, but easily at Type II [0].

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...](http://en.wikipedia.org/wiki/Kardashev_scale#Theoretical_examples)

------
johnchristopher
It's really hard to recommend one of my favourite novel this article reminds
me of without spoiling the whole story :(.

------
analog31
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.

~~~
has2k1
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.

------
JulianMorrison
Is there any way to rapidly repopulate the ozone layer? Assume unlimited
funding.

~~~
swombat
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](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](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
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?

~~~
pacala
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.

[http://www.fossilmuseum.net/Paleobiology/CambrianFossils.htm](http://www.fossilmuseum.net/Paleobiology/CambrianFossils.htm)

~~~
TheDauthi
The only problem with this is that we might not have long enough for multi-
cellular life to recover. While the red giant phase is a long way off, some
scientists think that the carbon cycle could shut down as little as 500
million years from now, either due to oceanic evaporation or due to a failure
in the weathering process.

------
lxe
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.

~~~
colordrops
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.

------
thesz
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.

------
cubano
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?

~~~
acadien
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.

------
dcre
Does this mean we could look for extraterrestrial civilizations by looking for
signs of planet-scale radiation shielding?

------
deft0nes
the font on this site is a threat to life

------
jcoffland
The article lost a lot of credibility for me with it's, "thousands of
millions." Apparently they think their readers are really dumb.

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chrisreichel
Cern Courrier are a threat to eyes.

------
viggity
can someone comment on the legitimacy/reliablity of the "Cern Courier". The
article seems legit (no tin foil hats), but that font. woof, it makes it look
super amateur.

~~~
indrax
>Produced for CERN by IOP Publishing

>©COPYRIGHT CERN 2007 for the content of CERN Courier and images and logos
identifying CERN.

>©COPYRIGHT IOP 2007 for the design, format and typography of the CERN Courier
Web Pages, ...

The author appears to be an astrophysicist, and you may know CERN from such
products as the Large Hadron Collider and the World Wide Web.

