Gamma ray bursts can sterilize whole galaxies..

[Brady Yoon]

In the astronomy encyclopedia, it says Gamma Ray Bursts may<A HREF=http://www.daviddarling.info/encyclopedia/G/gammaburst.html>be a solution to the Fermi Paradox... </A>

Are the really that powerful? I can't imagine something that releases that much energy..

[Manchurian Taikonaut]

It can happen perhaps, GRBs, Blazars and such have much power, but sometimes the space telescope have found massive bursts in Space. Giant Explosions, high-energy particles emitting radio waves, and huge Xray sources. Powerful Jets and perhaps a supermassive black hole collision can make the magnitude of the eruptions, if your Galaxy is small sized like the SMC cloud and in the wrong direction and a bad place then perhaps its bye bye for the chances of life going ahead

[Lance]

So when the GRB that takes us out does go off, will we know it?

Or will we just go from "sitting here posting quietly on the BABB" to "future alien archaeological dig" (sterilized planet with lots of cool stuff laying around) in an instant?

[Evan]

Hmm. Looks like the Drake equation may need some modification.

The rate of GRBs in the universe today appears to be about one burst per galaxy per several hundred million years.

It also seems that we are overdue for one.

[Arkyan]

It was my understanding that a GRB is something of a directional event, rather like a cosmic flashlight. If it happened to be pointing at you then you'd be toast, otherwise your planet would go along its merry way. It seems to me that if that is true, the idea of a GRB sterilising an entire galaxy seems a little farfetched. Is my understanding of GRBs incorrect, or is someone speaking in hyperbole?

[indie85]

This is clearly hyperbole, if one of these is supposed to happen in each galaxy per few hundred million years then earth should have been sterilised several times by now, I mean come on how small do they think a galaxy is??

[TravisM]

GRBs are thought to be the formation of early blackholes from the death throes of very large stars. Such stars would have formed in the very early days of the universe. The gamma rays are emitted from the poles of the newly formed black hole, and are due to its voracious appitite. It's as if the center of these huge stars turn into a gigantic black hole and the surrounding 'star suff' just cannot be 'exploded' away fast enough to overcome being 'ate'. :-? Lotta 'quotes' in there... hope ya'll follow me!
But yes, the GRBs are directional but are so far away (billions of light years in most cases) as to be relatively weak even when they are aligned with earth.
Trav

[collegeguy]

[quote="indie85"]This is clearly hyperbole, if one of these is supposed to happen in each galaxy per few hundred million years then earth should have been sterilised several times by now.

According to a report of space.com, they may explain the mass extinctions of the past. However, I guess you're right, because we would have been toast long ago.

[collegeguy]

What others bedides Eta Carinae are close to earth and could present a threat?

[Ilya]

The frequency of GRB's is not an exaggeration. The notion that one could sterilize an entire galaxy is very much so.

There is some evidence that supernova SN1987A produced a gamma-ray burst, but because it is not aimed at Earth, we did not see it as such.

[Ilya]

So when the GRB that takes us out does go off, will we know it?

Or will we just go from "sitting here posting quietly on the BABB" to "future alien archaeological dig" (sterilized planet with lots of cool stuff laying around) in an instant?

Only if it were REALLY close -- like within 100 ly. Even then, only the hemisphere facing the GRB would be instantly fried (although the other hemisphere would not last much longer.) At more realistic distances, I think the biggest killer would be nitric acid: practically all N2, O2 and H2O molecules in the upper atmosphere would dissociate, then recombine willy-nilly. Instant mother of all acid rains.

[geokstr]

If GRB's are really directional, can we only see them if they are pointed in our general direction? And if that's true, do they take that into account when they calculate their frequency in each galaxy?

Perhaps there are a lot more of them, but when they're pointed away from us we might not see them at all.

[Ilya]

If GRB's are really directional, can we only see them if they are pointed in our general direction?

Yes.

And if that's true, do they take that into account when they calculate their frequency in each galaxy?

I don't know.

Perhaps there are a lot more of them, but when they're pointed away from us we might not see them at all.

Very likely. The "evidence that supernova SN1987A produced a gamma-ray burst" is a "light spot" it made on the nebula surrounding the exploded star. Kind of what you see when someone points a flashlight to a side from you in a dense fog.

[collegeguy]

The frequency of GRB's is not an exaggeration. The notion that one could sterilize an entire galaxy is very much so.

There is some evidence that supernova SN1987A produced a gamma-ray burst, but because it is not aimed at Earth, we did not see it as such.

How can a GRB sterilize a whole galaxy?, I thought it only affected the part it was aiming at.

Can someone anwer my question of besides Eta carinae, what other ones are close and present a threat?

Is there a chance of a GRB ocurring near to us in the near future?

[Maddad]

Hmm. Looks like the Drake equation may need some modification.

The rate of GRBs in the universe today appears to be about one burst per galaxy per several hundred million years.

It also seems that we are overdue for one.

If a GRB were able to sterilize an entire galaxy, then we would have been sterilized a dozen times since life started here on Earth. They're not likely to be that powerful.

According to a report of space.com, they may explain the mass extinctions of the past.

One of the ideas tested by Walter Alveraez on the KT extinction event was a supernova being responsible for that mass extinction. He looked in the 2 centimeter thick layer for the plutonium that should have been produced, but found none. This disproved the hypothesis, so he looked elsewhere, eventually coming up with the asteroid/comet impact theory that we accept today.

A problem though with GRB's is that we are not sure exactly what their mechanism is, so we cannot say that an absense of any element disproves their causing an extinction. If we become confident of a mechanism, then we can look for its byproducts to supppor or reject a GRB's being responsible.

[geokstr]

Evan wrote:
Hmm. Looks like the Drake equation may need some modification.
Quote:
The rate of GRBs in the universe today appears to be about one burst per galaxy per several hundred million years.
It also seems that we are overdue for one.

geokstr asked:
Perhaps there are a lot more of them, but when they're pointed away from us we might not see them at all.

ILya responded:
Very likely. The "evidence that supernova SN1987A produced a gamma-ray burst" is a "light spot" it made on the nebula surrounding the exploded star. Kind of what you see when someone points a flashlight to a side from you in a dense fog.

Assuming the beam from a GRB is relatively tight, that would mean we would detect almost NONE of them. They would be too far away in other galaxies to infer them by their effect on nearby gas clouds, wouldn't they? And from as far away as distant galaxies, wouldn't they have to be aimed dead on straight at us for us to detect them at all?

If the answer to the above questions is yes, then given the nearly infinite number of directions a GRB could go in besides directly at us, I would think there might be a heck of a lot more of them than we now think.

Are we pretty sure they are only caused by cataclysmic events that we should be able to detect visually or at other wave-lengths, even at vast intergalactic distances, like a supernova?

[TravisM]

Well, when you figure that the HUDF shows a ton of galaxies in a speck of sky the odds that some GRBs are lined up with earth are pretty good.
The only other explanations are:
* GRBs are spherical in nature rather than beamed and the energy released is... just....
* GRBs are much closer than we think (pretty much disproven by the distribution...)

[Brady Yoon]

What others bedides Eta Carinae are close to earth and could present a threat?

The star Zeta Puppis, or Naos, has a mass of about 50 solar masses and its luminosity is 1 million solar. (It doesn't look that bright because it is over 1000 ly away and emits most of its light in the UV portion of the spectrum.) That's the only one I can think of. As far as I know, a star usually has to have 30+ solar masses in the beginning for it to collapse into a black hole and produce a GRB. Deneb, Rigel, Betelgeuse, Antares, while huge, are too small I think. But Naos is still in main sequence while Eta Carinae is on the verge of death.

*edited to add link

http://www.astro.uiuc.edu/~kaler/sow/naos.html

here's the link, i didn't use it so some info might be off.

[Brady Yoon]

Quick question, if a gamma ray burst occurred nearby, would it be noticeable with the naked eye? (Even though it's a GRB, is a lot of light emitted in visible wavelengths?)

[Evan]

Visible to the naked eye? It darn well should be. They spotted the light from one (not gonna look it up right now) that was way out there like 13 GLY. If that happened around these parts it ought to be brighter than the sun. Way brighter.

[Jpax2003]

What is the expected penetrating power of a GRB through solid and liquid matter? I know from my studies that gamma radiation from nuclear fallout can be shielded against by a few feet of packed earth, or less if you are using something denser like steel or concrete.

[Maksutov]

What is the expected penetrating power of a GRB through solid and liquid matter? I know from my studies that gamma radiation from nuclear fallout can be shielded against by a few feet of packed earth, or less if you are using something denser like steel or concrete.

You beat me to the punch.

Here are some examples of the effectiveness of various materials for gamma ray shielding. Note that the values are attenuations for 0.5 and 0.8 MeV gamma rays.

Therefore the Earth-impinging MeV value would need to be known.

But it certainly appears at first glance that for a short duration event (i.e., less than 6 hours), almost one half of the Earth's surface would be unaffected.

[Weird Dave]

Quick question, if a gamma ray burst occurred nearby, would it be noticeable with the naked eye? (Even though it's a GRB, is a lot of light emitted in visible wavelengths?)

Apparently one of the brightest GRBs seen reached optical magnitude 9. That's binocular visibility. I don't know how likely a nearby burst is, though.

[Tom Mazanec]

Greg Egan wrote a novel (Diaspora) using the colliding neutron star model of GRBs for one 16 LY from Earth. IIRC even the bacteria eventually had an Extinction Level Event, and nothing else survived on the planet at all (it happens over a millennium in the future, so a few people manage to protect themselves offworld and have all kinds of nifty adventures afterwards).

[Tom Mazanec]

Oh, and before you go woo-woo, Eta Carinae is not pointed at Earth (whew!).

[Evan]

Thinking about my post last night I have been trying to imagine a point source of light that is far brighter than the sun. That should cast some interesting shadows...

[Ilya]

The frequency of GRB's is not an exaggeration. The notion that one could sterilize an entire galaxy is very much so.

There is some evidence that supernova SN1987A produced a gamma-ray burst, but because it is not aimed at Earth, we did not see it as such.

How can a GRB sterilize a whole galaxy?, I thought it only affected the part it was aiming at.

That's why I wrote The notion that one could sterilize an entire galaxy is very much [an exaggeration].

[Evan]

I wouldn't feel quite so safe.

Here's how the estimate is figured: A setup called the Burst and Transient Source Experiment (BATSE) aboard NASA's Compton Gamma-Ray Observatory detected gamma-ray bursts (and presumably the associated hypernovae) at the rate of about 500 per year, or just more than one per day, in the observable universe, out to about 14 billion light-years.

Given that there are some 100 billion galaxies in that space, this rate translates into about one gamma ray burst from inside our galaxy beamed toward Earth every 200 million years. Because the energy is so concentrated compared to a normal supernova, hypernovae could potentially be harmful to life on Earth at much greater distances than supernovae.

http://www.space.com/scienceastronom...at_021216.html

[collegeguy]

I wouldn't feel quite so safe.

Here's how the estimate is figured: A setup called the Burst and Transient Source Experiment (BATSE) aboard NASA's Compton Gamma-Ray Observatory detected gamma-ray bursts (and presumably the associated hypernovae) at the rate of about 500 per year, or just more than one per day, in the observable universe, out to about 14 billion light-years.

Given that there are some 100 billion galaxies in that space, this rate translates into about one gamma ray burst from inside our galaxy beamed toward Earth every 200 million years. Because the energy is so concentrated compared to a normal supernova, hypernovae could potentially be harmful to life on Earth at much greater distances than supernovae.

http://www.space.com/scienceastronom...at_021216.html

Then, you are suggesting that Gamma rays possibly hit earth in the past and could do again in the near future. I mean, we should be overdue for one.

By the way, how long would it take the GR to get to earth considering they are light-years from us?

[Evan]

I'm not suggesting it, they are.