Newsgroups: sci.space.science
Subject: Re: Neutron star collisions wipe out alien races?
From: dmpalmer@clark.net.nospam (David Palmer)
Date: Wed, 19 Mar 1997 23:18:09 -0500 (EST)

In article <palmE70BB5.M6A@netcom.com>, palm@netcom.com (Palm
Computing) wrote:

> Hi.  I read an article recently discussing the observable flashes
> of X-rays.  Because the distribution of them doesn't corespond to the
> galactic plane it is believed that they are generally of extra galactic
> origin.  This would mean that a prodigous amount of energy is being
> released.  Given this the article proposes the collision of two neutron
> stars as a source of the X-ray bursts.
>
> The article also claims that such a release of energy would extinguish
> most lifeforms from planets within 1500 - 3000 light years.  It then
> went on to mention that three neutron binary star system lie within
> 3000 lights years of Earth.  None will explode tomorrow. :)
>
> My question is though, given the various assumptions for variables
> to the Drake equation, what the probability of one of these explosions
> which releases the X-rays, of destroying an alien civilization?
> Rough numbers are expected.  I'm really wondering if we could look
> up in the sky with our X-ray glasses and go poof - there goes another alien
> civilization!  Or could it be 1 in 1,000,000 explosions?  What's the
> daily attrition rate for alien civs?  This could be worse than a black
> hole at the center of every galaxy.


These Gamma-ray bursts (GRBs), if they are being seen at cosmological
distances, emit a supernova's worth of energy in a few seconds.  This means
that a GRB 1000 light years away will deposit the energy equivalent of
about a minute's worth sunlight in a few seconds.  That doesn't sound too
bad now, does it?

BUT

That energy is in the form of gamma-rays which don't reach the ground.
Instead, they are absorbed high in the atmosphere, and can break even the
strongest chemical bonds.

Steve Thorsett has a paper on the Terrestrial Implications of Cosmological
Gamma-Ray Burst Models, available at
http://xxx.lanl.gov/abs/astro-ph/9501019
or in an ApJ letter in 1995.  The abstract says

     ... If bursts arise from
      events that occur in normal galaxies, such as neutron star
      binary inspirals, then they will also occur in our Galaxy
      about every hundred thousand to million years. The
      gamma-ray flux at the Earth due to a Galactic GRB
      would far exceed that from even the largest solar flares.
      The absorption of this radiation in the atmosphere would
      substantially increase the stratospheric nitric oxide
      concentration through photodissociation of N$_2$,
      greatly reducing the ozone concentration for several
      years through NO$_x$ catalysis, with important
      biospheric effects due to increased solar ultraviolet flux. ...


The NO_x spreads throughout the atmosphere, so you're not safe if the GRB
didn't occur over your hemisphere.  Anybody on the planet who is
susceptible to UV had better stay inside during the day for a few years,
and keep his crops and other valuable ecosystems under glass.

But that is not necessarily the end of civilization.  Readers of
sci.space.science, and enough additional women to give the optimal
female:male ratio of 10:1 could move into mine shafts and breed
prodigiously Mein F.., I mean Mr. President.  As long as we do not allow a
mine shaft gap.



BUT


It may be that high-energy neutrinos from the neutron star collision have a
biological effect much worse than most people would expect based on low
energy neutrinos.  This was suggested by Juan Collar:
http://xxx.lanl.gov/abs/astro-ph/9505028
but this is inconsistent with the biological record for supernovae,
according to Abbas & Abbas:
http://xxx.lanl.gov/abs/astro-ph/9612003
although Collar disagrees and, while he's at it, disputes another
Abbas&Abbas paper:
http://xxx.lanl.gov/abs/astro-ph/9702026
(I haven't actually read all this correspondence yet.)

And if the neutrinos can kill you, you can't hide under a rock, or even a
planet, or anything less than another neutron star or a few light years of
lead.  "And the rock cried out 'No hiding place!'" to throw out a
gratuitous B5 reference.
http://www.hyperion.com/lurk/guide/064.html


And if the neutron stars aren't acting as pulsars (most aren't) then you're
unlikely to know about them before they do collide.  Your first indication
that something's wrong is that every cell in your body suddenly has a
high-energy recoil nucleus zipping through its DNA.  Since there's nothing
you can do about it, unlike the case of an incoming asteroid, would you
really want to know in advance?

Pleasant dreams.
--
            David Palmer
            dmpalmer@clark.net<remove '.nospam' in header>
            http://www.clark.net/pub/dmpalmer/

From: dmpalmer@clark.net.nospam (David Palmer)
Newsgroups: sci.space.science
Subject: Re: Neutron star collisions wipe out alien races?
Date: Thu, 20 Mar 1997 00:13:31 -0500

> >One problem with this line of reasoning is that even if Earth *has* been
> >really, really lucky for the last billion years, there should have been
> >several "near-misses."  It would be interesting to speculate that some of
> >the big die-offs (such as the end of the dinosaurs) were caused by
> >'nearby' neutron star collisions (perhaps 4,000 LY away?) but I think the
> >evidence for a big meteor strike 65 million years ago is pretty
> >overwhelming.
>
> You can have it both ways. While the energy from such an explosion might
> not sterilize a planet 4000 light years away, it would affect comets.
> They would be heated on the side towards the explosion, and this would
> cause material to boil off part of their surface. All the comets around
> a star would have their orbits perturbed by gas boiling off one side
> but not the other. A fraction of them would end up on orbits entering
> a planetary system, and hit various planets. In other words, such an
> explosion could trigger a "comet shower" and result in large impacts.
> This same mechanism has been suggested as a way a near-by supernova
> could cause a "comet shower." Going from a comet shower to the K-T
> impact and the extinction of the dinosaurs is a trivial step.


I thought of this a while ago but, at least for water ice and less volatile
material, the GRB would have to be deathly close to have much effect.
Gamma-rays are penetrating and deep-heating, like mentholatum.  As a
result, they deposit their energy throughout the top meter of the comet,
and so it will be insufficient to cause any outgassing unless the GRB is
close enough to melt the entire meter.  The X-rays (which are much less
penetrating) may flash-evaporate more volatile ices at the surface (e.g.
methane ices?) so that might be the most important effect.

Even at 1000 A.U., orbital velocity is a kilometer per second.  Assume that
you need to kick the things at 10 m/s to get some of the comets to take the
first steps towards visiting our friendly planet.  (A very very very small
fraction of oort cloud objects are in orbits close enough to reach the
orbits of gas giants under the influence of such a small kick, but there
are very very very many oort cloud objects, and once one encounters a gas
giant, it can go whereever it wants.)

Assume that the reaction mass is methane at its melting temperature of 90 K
-> kT = 8e-3 eV -> RMS velocity = 500 m/s.  Therefore, if you just barely
melt the methane and let it emerge through crevices which just happen to
look a lot like rocket nozzles all pointing in the same direction, you have
to evaporate 2% of the mass of the comet (10 m/s / 500 m/s) to give it the
desired kick.  This is the most energy-efficient way to move things: use as
much reaction mass at as low a velocity as possible.  (It is the least
reaction-mass efficient way, which is why it is not used much in modern
space rockets.)

For a 100 meter city smasher that might be doable, but for a 10 km dinosaur
killer, that means you either have to melt 200 meters of methane (although
the gammas only penetrate to a few meters) or you have to get the reaction
mass a lot hotter than methane's melting temperature.  If you ablate to 10
meters deep, a long estimate of the gamma penetration depth (10^-3 of the
comet's diameter) then you would need to heat the material to a velocity of
10 km/s (10^3 of the required delta-v).  If the gamma-ray burst is intense
enough to do this to a comet, what it does to Earth would make any
subsequent comet shower relatively unimportant.

N.B. some of my numbers may be a bit off.  I am breaking my rule of 'if you
are too tired to use heavy machinery, you are too tired to post to usenet'.
--
            David Palmer
            dmpalmer@clark.net<remove '.nospam' in header>
            http://www.clark.net/pub/dmpalmer/

From: "David M. Palmer" <dmpalmer@clark.net>
Newsgroups: sci.space.policy
Subject: Re: Could humanity survive a GRB?
Date: Sat, 06 Nov 1999 21:21:58 -0500

In article <ZDhgaym.frankglover@delphi.com>, frankglover@delphi.com
wrote:

> <gigantin@shore.net> writes:
>
> >In the "Where are they?" thread, Joe Strout brought up
> >the possibility of gamma ray bursts periodically "sterilizing
> >the galaxy", destroying most of the life present in it.
>
>
>    Though naturally not as much of a hazard, the occasional supernova doesn't
> help either. According to an Asimov essay I read long ago, they'd be
> dangerous out to at least 10 light years....

See
http://stupendous.rit.edu/richmond/answers/snrisks.txt
for supernova risk information.

>
>
> >Is it possible that humanity could protect itself and
> >some of the Earth's biosphere from a GRB, given sufficient
> >warning? What steps could be taken for protection?
> >I am wondering if living underground would provide enough shelter,
> >or  perhaps, living deep underwater? Would developing space still
> >be feasable in the increased radiation environment?
>
>
>    Some habitats (espically on the Moon) will tend to be underground anyway,
> and that assumes the GRB is high in the sky and not above the opposite side
> of the planet. Which leads me to a question...how long does a GRB last? If
> hours, then basically only one side of a planet is at immediate risk. (Yes, I
> know this could still be massively environmentally damaging, but still not as
> unrecoverable as if all hemispheres had to face the music.) If it's deveral
> Earth days, then one has a real problem.

GRBs are short (varying from a few milliseconds to a few minutes), so
only one side of the planet will be hit by the main gamma-rays.  But...

Gamma-rays do not get through the atmosphere (which is equivalent in
thickness to a few feet of lead).  The atmosphere stops the gamams at a
range of altitudes, including around the ozone layer.  The absorbed
energy causes molecules in the air to break up and recombine, leading
to oxides of nitrogen.  These nitrogen oxides catalyze the destruction
of the ozone layer.  They are persistent enough that they will drift to
cover the entire globe, and soon every place on the surface is bathed
in ultraviolet light.

By that point, the biosphere is having a Very Bad Day.  But anybody who
wants can sit in the shade and watch the planet die around them.

What comes next is a bit more speculative.  It is likely that the GRB
is a source of high energy particle radiation, cosmic rays.  These
cosmic rays (or, more precisely, secondary particles generated in the
atmosphere by these primary cosmic rays) irradiate the Earth.  The
cosmic rays travel more slowly than light, so they come somewhat after
the gamma-rays, and last somewhat longer, letting the planet rotisserie
under their beam.  You have to get under a lot of material (rock or
water) to block these sufficiently to survive without radiation
sickness or cancer.

I would not rule out the chance to preserve a nucleus of human
specimens. It would be quite easy...heh, heh...at the bottom of
ah...some of our deeper mineshafts.  Nuclear reactors could provide
power almost indefinitely. Greenhouses could maintain plantlife.
Animals could be bred and slaughtered...Dwelling space for several
hundred thousands of our people could easily be provided.  I would hate
to have to decide...who stays up and...who goes down.  Well, that would
not be necessary. It could easily be accomplished with a computer. And
a computer could be set and programmed to accept factors from youth,
health, sexual fertility, intelligence, and a cross section of
necessary skills. Of course, it would be absolutely vital that our top
government and military men be included to foster and impart the
required principles of leadership and tradition.

Naturally, they would breed prodigiously, eh? There would be much time,
and little to do. Ha, ha. But ah, with the proper breeding techniques
and a ratio of say, ten females to each male, I would guess that they
could then work their way back to the present Gross National Product
within say, twenty years.



--
        David Palmer   dmpalmer@clark.net
        http://www.clark.net/pub/dmpalmer/

From: "David M. Palmer" <dmpalmer@clark.net>
Newsgroups: sci.space.policy
Subject: Re: Could humanity survive a GRB?
Date: Tue, 09 Nov 1999 08:41:38 -0500

In article <8080lv$2du@peabody.colorado.edu>,
fcrary@rintintin.colorado.edu (Frank Crary) wrote:
> In article <081119991759081531%joe@strout.net>,
> Joe Strout  <joe@strout.net> wrote:
> >> Fortunately, this is a moot point. Gamma ray bursts seem to occur at
> >> cosmological distances, which implies that they only happen in young
> >> galaxies. On the other hand, if this is incorrect, and they do happen
> >> in our own galaxy or nearby intergalactic space, then the are much
> >> weaker than current estimates suggest.
>
> >Frank, couldn't it be that the GRBs are pretty uniformly distributed
> >among the galaxies -- most since most of the billions of galaxies are
> >very far away, it so happens that the GRBs we've been able to measure
> >(only a few dozen, I believe) are very far away?
>
> ...apparent brightness would be proportional to 1/r^2, where r is the
> distance to the object. The rate of events would be proportional
> to r^2 if the events were uniformly distributed in space. Combining
> these two relations, the rate of events would be proportional
> to one over their apparent brightness. I'm fairly sure this is
> not what they observe....

The data is currently consistent with the idea that the rate of GRBs is
proportional to the star formation rate.  There is some evidence that
GRBs tend to occur in star forming regions.  This is consistent with
the idea that GRBs are core-collapse events in massive stars, akin to
Type II supernovae.  Type II supernovae do indeed occur near to us (the
supernova that produced the Crab Nebula and SN 1987A to name just two
nearby examples.)

The number-brightness relationship is inconsistent with uniform
distribution in Euclidean space.  However, the direction of the
deviation indicates that there are fewer dim (distant) GRBs than you
would expect from the number of bright (nearby) ones.  this was the
first compelling evidence that GRBs come from far outside our Galaxy,
way out where the Universe starts to run out of space and time.

We have redshifts for less than a dozen GRBs.  I think the current
record for the most distant reliable redshift is z=3.48 .  If that is a
typical distance for the faintest bursts we can see (that particular
burst was a bright one), and ignoring all the cosmological factors that
you can't ignore, that would mean that only about one GRB in a thousand
would be expected closer than z < 0.3.

We need to get a lot more GRBs in order to do population statistics.
Fortunately, NASA has just committed to a new spacecraft, capable of
detecting GRBs and immediately observing them with optical and X-ray
telescopes and finding their redshifts.

This mission, Swift, will detect and measure hundreds of GRBs per year,
and will answer many of the questions we currently have about GRBs.
For more information, visit our website:
   http://swift.gsfc.nasa.gov
Launch is scheduled for July 31, 2003.



--
        David Palmer   dmpalmer@clark.net
        http://www.clark.net/pub/dmpalmer/

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: Do we have the tech to create a lifeboat for humanity?
Date: Thu, 12 Oct 2000 17:30:56 -0500

Josh wrote:

> > Huh???
> >
> > The Earth is considerably thicker than any asteriod.  And why would
> > digging 200 meters into an asteriod be any easier than digging 200 meters
> > into the Earth?
>
>  Gravity, an O'Neil type colony inside an asteroid might be cheaper than
> trying to support 1,000 tons of overburden for each square meter of
> cropland.


Actually, you'd probably need less than that.

The lethal effect from gamma ray bursters comes from the
cosmic rays (protons, mainly) they produce.  The scenario
is: these come to earth of a period of months, hitting
the upper atmosphere.  The collisions produce pions, which
decay to muons.  The muons are what can penetrate deeply
into the ground.

The pions can decay because air has low density.  If the
pions were produced in rock or some other solid, they'd
mostly be absorbed by nuclear collisions before they could
decay.  This would greatly reduce the muon flux.

	Paul

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: Do we have the tech to create a lifeboat for humanity?
Date: Fri, 13 Oct 2000 18:37:57 -0500

Mike Combs wrote:

> So what thickness of soil (whether terrestrial or asteroidal) WOULD we
> need to survive a GRB?

That I couldn't say offhand.

Earth has another problem: the cosmic rays would induce
a great deal of radioactivity in the atmosphere (14C),
which would (IIRC) render the planet uninhabitable even
after the prompt radiation had died away.

	Paul

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: Do we have the tech to create a lifeboat for humanity?
Date: Sat, 14 Oct 2000 06:07:51 -0500

Filip De Vos wrote:

> This is the reason why I do not beleive in GRBs. If GRBs are common (for
> instance, being an explanation for the Fermi paradox) then they should
> have happened during the existence of the earth (5 billion years). The
> fossil/geological record should carry one or more layer(s) with the
> nuclear debris/effects embedded in them. There is no such layer, ergo,
> there were no GRBs in the Earth's history, therefore, there were none in
> the past.

14C would leave no long-lived isotopic evidence.
It decays back to 14N, which is what it's produced
from.  10Be is longer lived, but still would decay
away.  Most of the isotopes, btw, *would* be produced
in the atmosphere, not in the ground.  The muons
that reach the ground are not terribly good at
causing nuclear reactions (that's why they can reach
the ground.)

It might be more worthwhile to look for evidence
on bodies in space without atmospheres.

	Paul

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: Do we have the tech to create a lifeboat for humanity?
Date: Sun, 15 Oct 2000 04:19:38 -0500

Filip De Vos wrote:

> ... but would all Gammas be absorbed in the atmosphere and trigger muon
> production? I thought that most of the Gammas would penetrate all the way
> to the ground, wreaking havoc there on the biologicals.

You misunderstand.  The gamma rays in the burst itself
are not the cause of this problem.  It's the charged
particles from the fireball that are the problem.  This
fireball radiates some of its energy in gamma rays
(which we see as a burst) but is thought to put much
more energy into the charged particles.

The gammas would most certainly *not* penetrate
to the ground, btw, in any significant number.
The atmosphere is far too thick.  That's why they use
satellites to detect GRBs, after all.  They could
cause NOx formation and ozone destruction, but that's
a *relatively* minor disaster.

	Paul