Mass Extinctions and Gamma Ray Bursts

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Supernova -> (gamma rays) -> destruction of ozone layer -> excessive ultraviolet radiation from the Sun.

Whether this scenario is regular or not depends on your view on the regularity of a supernova within the distance of 10,000 light years from the Sun.

Hi satt: If the most powerful supernova possible (at 10,000 lightyears) removes 50 % of the ozone from Earth's upper atmosphere; will the weakest possible supernova at 3000 lightyears do even worse damage? How many O,B,A and F stars are presently within 10,000 light years? I don't think G, K, and M stars can go super nova. Is 1% per million years going super nova a reasonable estimate? Would a 50 % reduction in upper atmosphere ozone, kill mamals at a much increased rate or would the cancer rate double which would only reduce the fertility by perhaps 10 % typically. Any clues will be appreciated. Neil

Hi neil..

Unless it is a hypernova, an origin of the gamma ray burst, a supernova is said to be not very dangerous it it occurs outside of 26 light-years.

-- "The study, led by Neil Gehrels of NASA's Goddard Space Flight Center, found that for a supernova to significantly deplete ozone it would have to occur within 26 light-years of our planet. Other data shows that this happens only about once in a billion years."

One gamma ray burst from inside our galaxy every 200 million 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."

Quotation from the next link:

http://www.space.com/scienceastronomy/supernova_threat_021216.html

So Sirus is the only supernova hazard near term, or are there other class f or bigger within 26 lightyears? I suppose several could move that close over the next billion years. If the proper motion is 0.0001 c = 18.6 miles per second; a star could come 100 light years closer to Earth in one billion years.
So it is the gamma ray bursters that could blow away much of Earth's upper ozone layer from up to 10,000 light years away. I suppose some of the Xray bursts we detect are gamma that has red shifted? Does the intense part of a gamma burst last seconds, minutes, hours or days? All of the above perhaps? Neil

It is said that it lasts from a few milliseconds to several minutes.
In the following link you can find a simulation of a gamma ray burst.
(caution: 10MB; QuickTiime is required)

http://imagine.gsfc.nasa.gov/Videos/news/GRBstar2.mov

A rate of 1 per 200My seems roughly similar to the mass extinction periodicity on Earth. It's not exact, but then, you wouldn't expect it to be. Extinctions can also occur from asteroid impacts, vulcanism and other possible unknowns.

Also, the level of sterilization around a GRB occuring at that rate covering areas as large as galaxies, might give some clue as to why we don't see galaxies swarming with life. Just as life on planets is peroidically decimated by global disasters, so might whole galexies be similarly affected by periodic GRB's. It's possible that the general evolution of life in galaxies as a whole, goes through much the same cycle of advance and decline that global systems do. This might account for "The Great Silence" described by the Fermi Paradox.

rosborne979..

As to your partial solution to the Fermi Paradox, I would like to say that if you think the evolution to an intellectual life is a complex of phenomenal randomness and natural selection then the GRB is already included in the random events along the course of the evolution of life.

Possibly true, but then again, we didn't even know about GRB's until recently, much less that they could have an effect on planetary evolution. And we don't yet know for certain... but it's beginning to look like it could be a major component of the equation; a component which, unlike asteroids, affects large portions of a Galaxy. An interesting component to consider at the least.

Just for grins I think the Fermi Paradox (or problem) is one of the best arguements favoring the Big Bang-Expanding Universe theory.

I have another though, a little more "mechanical" :wink: in nature. Perhaps the time required to evolve "intelligence" to the point where intergalactic or even intersteller communication takes longer than a planet remains livable.

If Earth dies or her resources are used to the point where no surplus is availiable for astronomical forays then we will have lost our chance for a trip to the stars forever.

Personally I am afraid that this is what happens and thus we can have either type of universe (BB or infinite) with no intersteller communications.

We already leak our communications into space, and we are already sending probes out of our solar system.

The real "trick" with the paradox is figuring out when Von Neumann machines enter the picture. For once self replicating machines get going, there is little in space to stop their proliferation. Space is perfect for machines; cold and clean and full of energy and raw material.

The Fermi Paradox doesn't limit itself to biological intelligence. Our own progress with technology, in such a fantastically short period of time seems to indicate that biological intelligence may be just a necessary precursor to self replicating mechanical intelligence.

Of course, machines wouldn't necessarily be destroyed by the secondary effects of a close GRB, so I guess I'm back to a paradox again...

Rosborne,----Already

Eight billion years, perhaps half or more of a star systems allotted time.

A million and a half years or so since the dawn of "self awareness".

Even if intelligence expands at an exponential rate will that be enough time to permit our little trip to Andromeda or points beyond

Apparently no other society has been able to.

IMO Regretfully

Hi Aka,



Our Sun is considered to be at least a third generation star (based on content of heavy metals), which means at least three other Earth evolution cycles could have occurred already since the Big Bang.

We know that life on our planet began very quickly. In geologic terms, almost as soon as the rocks had cooled. Maybe this is a unique event, or maybe not, but if we assume not...

Then granted that it took 3.5 billion years for self awreness to arrive, but the universe is 13.7 billion years old, and the distance between galaxies may be uncrossable, but the time it takes to colonize a standard galaxy with a diameter of 100kLy is much less than a billion years, even crawling along with the technology we have today.

So, even a single successful civilization out of the billions of stars in every galaxy *should* be capable of colonizing the whole galaxy well within the lifespan of its progenitor planet (assuming of course that our situation is not unique).

So Yes, we are *already* here. And more importantly, our galaxy and all others should be swarming with Von Neumann machines at least three times over since the Big Bang, and yet, they are not. This is the Fermi Paradox, and it's a good one. Either the conditions we have as examples are unique (though increasing evidence shows more and more environments which are similar to proto Earth), or we're missing something fundamental in our understanding of what limits life in the Universe. Or, the Universe is full of intelligent communicative life, and we just don't recognize it for some reason.

Best Regards,

PS, the links in my previous post lead to more detailed information on the Fermi Paradox, and to Von Neumann machines.

Yes, it should have happened!

Or perhaps the limitations imposed by finite amounts of time availiable in a limited system (stellar, galactic or universal) acts as a constraint upon intelligence thus precluding intersteller communication.

Darned if I know, and I have never run across even a possible reason as to why not

intersteller communications is not as easy as most people think. Someone said a cell phone on one of the moons of Jupiter could be detected by the Aricibo Radio Telescope; presumably just barely or they would have suggested moons of the more distant gas giants which have less radio noise. If the cell phone is one watt we need a trillion watts to be detectable one million times farther away (square Law) If Jupiter is 450 million kilometers away times a million = 450 trillion kilometers = 45 light years. With present Earth technology, an effective radiated power of a trillion watts is possible only with a very high gain antenna which transmits in a very narrow beam. (none of the TV or radio stations, perhaps none of the satellite up links, which are very broad band compared to a cell phone. Wide band means more effective radiated power is needed to be detectable. At any instant the probability is only about one in a thousand that the beam is illuminating any planet within 40 light years, even if there are 100 planets that close. We probably have not refined the orbits of any of the extra solar planets sufficiently to know their position when the beam arrives in 40 years so we really can't track any of the extra solar planets with our very high gain transmitting antenna. Can ET track Earth from 40 light years away? Perhaps. Neil

Perhaps Earth slipped though the cracks following our colonization a million years ago along with 100 million other planets in our galaxy. The Earth colony did poorly. We are the descendents of the survivers. Due to a bureaucratic slip up (or coverup) Earth has not been visited recently. Neil

Neil,

IF we were populated from another system I would expect some sort of break in the progression of complexity.

There does not seem to be one. As far as I can understand the "pop" literature, from the simplest self replicating molecule to man we are all related to each other.

(or we are all Von Neumann Machines)

I do not think these links are out of place here.

Nasa to abandon Hubble telescope

http://news.bbc.co.uk/2/hi/science/nature/3405249.stm


"Nasa is halting all space shuttle missions to service the Hubble Space Telescope, a move that will lead to it becoming useless within five years."


Hubble obtains deepest space view

http://news.bbc.co.uk/2/hi/science/nature/3387919.stm

"The Hubble Space Telescope has imaged the deepest view ever of the cosmos, detecting the youngest and most distant galaxies ever seen by astronomers."

Thanx Satts,

Surely a mixed blessing, but are we sure that we can't have them both?

Personally, do you think that when the pictures are processed they'll look a lot like here? I am referring back to our discussions on the universe and space thread.