Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: briligg on 28/08/2012 22:24:46
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Just as a fun, apocalyptic tv series kind of thought experiment, how would that play out for us? Is 10 light-years enough for the full Mad Max effect, without wiping us out completely?
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A supernova at 10 ly would certainly destroy all life on earth and a type 1a would probably destroy the earth too. I don't think there are any candidates that close though, so we may be OK :-) Even at 3000 ly a type 1a Supernova could wipe out the earth's ozone layer and cause mass extinctions, and I expect there to be plenty of candidates within that range.
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Wikipedia even has a list of Supernova Candidates (http://en.wikipedia.org/wiki/List_of_supernova_candidates)
Keep in mind that the larger stars have a shorter lifespan than the smaller stars, so any star that is currently significantly larger than the sun will likely go supernova long before our sun expands to the red giant phase and slowly dies.
At about 150 lightyears, the closest is IK Pegasi (http://en.wikipedia.org/wiki/IK_Pegasi). It is not as large as some of the stars, but it is considered to be a supernova candidate due to interactions with the binary system and a large white dwarf.
The next few more massive stars are 500 to 1000 lightyears away, or more.
Betelgeuse (http://en.wikipedia.org/wiki/Betelgeuse) at about 640 lightyears distance is destined to go supernova in the next few million years. In the current configuration, the gamma ray burst is not expected to impact Earth, but would that change as we orbit around the Milky Way?
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A supernova at a distance of 10 light years would be about as bright as the sun at peak brightness. Having two suns in the sky for a while would certainly do the planet quite a lot of harm. The ionising radiation effects would be very considerable but as to whether it would totally destroy all life I somehow doubt.
It would be a cataclysmic event that both ordinary and intelligent life could survive particularly if they knew that it was coming.
Some aspects of the way our planet works would naturally protect it for example heavy evaporation from the oceans would create much more cloud cover and reduce the effect of the extra heat input.
We have a potential supernova reasonably close in the Form of Betelgeuse but that is around 640 light years away 64 times as far and so would be around 2000 times fainter than if it was only 10 light years away that is around nine or ten stellar magnitudes which would make it around as bright as the full moon
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SS, wouldn't the intensity radiation fall off as the inverse square of the distance? So 64 times the distance would be 1/4096th of the radiation rather than 1/2000th. Similarly a supernova at 10 ly (compared with 500 l.secs) would be only 0.025 of the radiation even allowing for the peak brightness to be 10 billion times brighter than the sun. I don't think the problem is the luminosity but the spectrum of the energy which is rich in gamma radiation.
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Wikipedia's Gamma ray burst (http://en.wikipedia.org/wiki/Gamma_ray_burst#Rates_and_potential_effects_on_life_on_Earth) answers this question directly, i checked it out since you mentioned GRBs. Nasty. At least if we weren't lined up with one of the star's poles it would only be a fancy light show.
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But since a GRB only lasts a few seconds, wouldn't the life on the far side of the planet have a chance? Even if the ozone is stripped away, could humans make it through if they were deep underground, and could they then adapt to the post-apocalyptic aftermath?
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I think the atmosphere can get damaged too. I have never looked into this as it is a bit hypothetical. At least the ozone layer goes but it may well be that there can be adaptation. I think that it would be very unlucky to be in a polar gamma ray jet however.
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If the gamma ray burst is short (minutes or hours), then not only would half the planet be shadowed, but a large fraction of the ozone would also be shadowed, and would eventually spread around the planet again (likely quicker around the planet than North to South).
Ozone is generated by the sun, which is why the polar ozone holes only occur in the winter without sunlight, and mostly disappear in the summer when the sun is out.
Would the gamma burst both destroy & manufacture ozone?
Anyway, it is quite likely that the ozone would at least partly recover within a few months, and mostly recover in less than a couple of years.
The actual supernova could last a couple of months. But, the effect on Earth of a "second sun" would be dependent on which direction it is.
If it was on the same side of Earth as the sun, then parts of Earth could get a "double-dose" of sunlight which could be bad.
If it was on the opposite side of the Earth from the sun, and occurred in either the summer or winter, then it would cause half to earth to have a very mild winter, and the other half to only be marginally warmer in the summer. Such a mild winter could have both positive and negative ramifications. And, of course, it would be odd to have extended daylight hours which could be disruptive to some animals.
Still, with it on the same side of the Earth as the sun, the impact may still be far greater for the summer hemisphere than the winter hemisphere.
Likewise, if it occurred over the poles, one hemisphere would be largely unaffected. The other other hemisphere would have either a harsh summer or mild winter depending on the season. And, again, extra winter sunlight could be both beneficial and harmful including significant impact to the ice cover, as well as animal habitat, but might not be lethal to humans.
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I wonder if the extra light energy could be enough to increase storm activity, especially hurricanes.
For the amount of damage the gamma radiation could do to life, it does seem to me like there should be more upshot indirectly. Like the ultraviolet roasting that comes after the gamma ray burst - wouldn't that all eventually be absorbed as heat? That also makes me think we could have some extremely violent hurricane/tornado/general storm activity.
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According to a New Scientist article the effects of radiation from a nearby supernova can last many 100s of years and are capable of causing mass extinctions:
http://www.newscientist.com/article/dn1764-supernova-smoking-gun-linked-to-mass-extinctions.html
They cite one from a supernova that would have been 130ly from the solar system about 2m years ago which could have been responsible for the extinction of marine molluscs.
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Interesting about ancient supernovas.
One thing the article doesn't discuss is that gamma rays and cosmic rays (particulate matter) travel at different speeds. So, if a supernova occurred 100 lightyears away, the gamma rays would arrive 100 years later. The cosmic rays would arrive significantly later. How fast would they be travelling? Is there stratification with the lighter elements potentially travelling faster and arriving earlier than the heavier elements?
Perhaps high density cosmic rays (and asteroids?) would be one of the things that would extend the effects of the supernova.
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I heard a suggestion that a "nearby" supernova could impact us in an unexpected way: via neutrinos.
Neutrinos don't often interact with matter - it is said that about a billion neutrinos from the Sun pass through an area of a fingernail, every second, and nearly all of them pass right through the Earth.
However, in 1987, a Supernova in the Magellanic satellite galaxy produced a burst of neutrinos, 24 of which were detected by some large detectors on Earth (http://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions). This is 168,000 light-years away.
At 10 light years away, a supernova would be about 300 million times more intense. This could cause an increase in cancers - and the thickness of the Earth would not provide any useful shielding.
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So, a few days after the gamma ray burst, when the small number of people who had sufficient warning and an option stick their heads out of their bomb shelters or sub-basements or subway tunnels or what have you on the planet's near side, they'd find all people, plant and animal life on the surface dead or dying from massive gamma radiation doses. The whole planet would still be dealing with the ultraviolet radiation that follows the GRB, meaning even on the far side, most or maybe all vegetation would be dead or dying, and all animal life not able to take sufficient shelter would be nastily sun-burnt (dying-star-burnt). A stripped off ozone layer would make that even worse, and ground-level ozone may also have been generated in sufficient quantities to affect living organisms. Marine organisms would be alright, unless they were sensitive to the huge inundation of normally rare isotopes of various elements generated by the radiation, or they were affected by the run-off of rotting dead stuff from the land.
Presumably all electronics on the near side would be fried, and maybe most of the stuff on the far side too. Extreme weather would likely occur for decades.
Who needs zombie apocalypse shows? I'd rather watch this series.
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Btw, i'm guessing that when the New Scientist article said 'Clayton says 60Fe would be blasted towards Earth when high energy neutrons from the supernova core smack into iron atoms in its outer shell.', what it meant was that neutrinos were blasted towards Earth and created 60Fe when they interacted with iron atoms already in the crust. Allow me to take a moment to express how much it annoys me when science magazines, of whatever reputation, make mistakes like this. I'd adore being paid to write that stuff, how many people get that chance? And yet these mags have so much staff who are obviously shaky on a lot of 1st year university science, and even their editors don't catch it. And the public is mis-informed.
(Scratch that re: this New Scientist article - a closer reading shows i didn't get it right. But still. I jump the gun partly because i've found errors in mags so often.)
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Btw, i'm guessing that when the New Scientist article said 'Clayton says 60Fe would be blasted towards Earth when high energy neutrons from the supernova core smack into iron atoms in its outer shell.', what it meant was that neutrinos were blasted towards Earth and created 60Fe when they interacted with iron atoms already in the crust.
I thought the current theory was that many of the heavier elements are actually created during the supernova. So, most of the stars generate power by fusing hydrogen and helium to make the lighter elements. But, then in the final moments of the supernova, the heavier elements such as Iron are formed IN THE STAR. And even the heavier elements such as Uranium are formed, requiring more energy input than the energy that is gained through their formation.
Then the supernova spreads these elements around the stellar neighborhood, at velocities significantly less than the speed of light. Although I was seeing notes that some cosmic rays may in fact be travelling as high as half the speed of light. But, they still would arrive significantly after the gamma rays and neutrinos.
This is different from the formation of Carbon-14 (14C) (http://en.wikipedia.org/wiki/Carbon-14#Origin_and_radioactive_decay) which is formed in Earth's atmosphere by the solar wind and cosmic rays interacting with Nitrogen.
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If a star is large enough, after it has finished fusion of most of its hydrogen to helium, it can continue fusing heavier elements, until the core is made up of elements like iron and nickel (found in certain certain classes of meteorites).
However, nuclear processes consume energy to build a nucleus beyond 56 nucleons. It is thought that the elements beyond Iron-56 are built in an intense burst of neutrons that accompany a supernova explosion.
So the Iron-60 could have built up by Iron-56 being bombarded by neutrons, or by decay of even larger nuclei formed in a supernova.
It is thought that much of the momentum imparted to the supernova debris comes from neutrinos. The density of the atoms collapsing towards the center of the star to form a neutron star is sufficient to interact with the normally elusive neutrinos, blasting the surface into space.
http://en.wikipedia.org/wiki/Supernova_nucleosynthesis#Supernova
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I am confused by some parts of the New Scientist article. 130 ly is very close, but i thought the atoms from the shock wave travelled so slowly they wouldn't be closely associated with affects from the radiation waves even in geological time. Guess i'm wrong there. And i'm confused about why marine molluscs are the species that really got it. Even living under several meters of water? Are they just the species that show up in the fossil record, but many other species died too (especially plants)?
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The molluscs suffered as a consequence of UV-B damage to phytoplankton. The original paper on the subject is here...
http://arxiv.org/pdf/astro-ph/0201018.pdf
It is all rather speculative but it is nonetheless plausible.
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What about the ozone hole over the antarctic and now also the arctic?
I'm guessing that the same mechanisms we see now will be the ones involved in a world wide depletion of ozone. And instead of healing we're getting new and bigger ones. They create a colder climate (locally) as the ozone disappear, but with it you also get cancers and damage to all living things, be they plants or humans.
"According to the study, occurrence of the Arctic ozone hole was mainly due to the extraordinarily cold temperatures in the ozone layer that is located at about 18 km height in the stratosphere, i.e. the second layer of the earth's atmosphere. There, chlorine compounds originating from chlorofluorocarbons and other pollutants are converted chemically at temperatures below -78°C.
These chemical conversion products attack the ozone layer and destroy it.
If the trend for colder temperatures in the stratosphere observed in the past decades continues, repeated occurrence of an Arctic ozone hole has to be expected. The team of IMK researchers analyzed measurements of the chemical composition of the atmosphere by satellite instruments. In addition, model calculations were made to determine concrete effects of further cooling of the ozone layer. 'We found that further decrease in temperature by just 1°C would be sufficient to cause a nearly complete destruction of the Arctic ozone layer in certain areas,' says Dr. Björn-Martin Sinnhuber, main author of the study.
Observations over the past thirty years indicate that the stratosphere in cold Arctic winters cooled down by about 1°C per decade on the average. "
Weird isn't it, we both create a warming as well as a, locally seen, cooling. But the bottom line is that neither of those are especially good for our continuing existence on Earth.
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yor_on, environmental issues are indeed going to get a lot worse before they get better, and i for one believe that we will be forced to do extensive environmental engineering in order to avoid a cataclysm. Perhaps that is why i am more interested in post-apocalyptic fiction that i used to be, and why it is so in fashion in general. But i have faith in humanity. We have not quite become as gods, but considering how powerful we have become, how quickly, i don't think we should be too hard on ourselves for our rookie screw-ups. Give us another 50 to 100 years, and we will be the caring stewards of the earth, the role evolution has obviously placed upon us.
Anyhow, it is deserving of another thread. I imagine there are several. From a post-supernova standpoint, our little seasonal ozone holes are laughable.
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graham.d - now that it is Saturday, i'm tackling that excellent arxiv article. Thanks for supplying the link!
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Wish I could agree.
They're not laughable, quite big in fact, the antarctic still being the largest. And any scenario trying to guess what happens as Earths ozone layer disappear will do well in studying those we have. Take a look here. (http://www.popsci.com/science/article/2011-10/so-now-there%E2%80%99s-ozone-hole-over-arctic-what-does-mean)
"The 2011 Arctic ozone loss occurred over an area considerably smaller than that of the Antarctic ozone holes. This is because the Arctic polar vortex, a persistent large-scale cyclone within which the ozone loss takes place, was about 40 percent smaller than a typical Antarctic vortex. While smaller and shorter-lived than its Antarctic counterpart, the Arctic polar vortex is more mobile, often moving over densely populated northern regions. Decreases in overhead ozone lead to increases in surface ultraviolet radiation, which are known to have adverse effects on humans and other life forms.
Although the total amount of Arctic ozone measured was much more than twice that typically seen in an Antarctic spring, the amount destroyed was comparable to that in some previous Antarctic ozone holes. This is because ozone levels at the beginning of Arctic winter are typically much greater than those at the beginning of Antarctic winter.
Manney said that without the 1989 Montreal Protocol, an international treaty limiting production of ozone-depleting substances, chlorine levels already would be so high that an Arctic ozone hole would form every spring. The long atmospheric lifetimes of ozone-depleting chemicals already in the atmosphere mean that Antarctic ozone holes, and the possibility of future severe Arctic ozone loss, will continue for decades.
"Our ability to quantify polar ozone loss and associated processes will be reduced in the future when NASA's Aura and CALIPSO spacecraft, whose trace gas and cloud measurements were central to this study, reach the end of their operational lifetimes," Manney said. "It is imperative that this capability be maintained if we are to reliably predict future ozone loss in a changing climate." "
So, what conclusions can we draw here. Satellites, we need more but? They 'cost' too much, and are very uncomfortable for those denying a global warming as they actually transmit real live data as it happens, and can do so for decades. Also that Earth is a very tricky 'system', open ended to Space and with new and surprising twists every, well maybe not day, but they will come closer in time as the warming continues. As always peoples greed will stop the research needed, as long as they can't see a 'profit' for themselves.
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Well, i only used the word laughable in relation to what a supernova at 10 ly would do. It is a serious problem, i don't discount that.