[Mobius]

Did you miss the part where it would kill everything on the side of the planet facing it?

Extremely unlikely.  Supernova's have been witnessed in past history...its rare but not completely unheard of.

A supernova might have caused a mass extinction at the end of the Ordovician:

Gamma ray burst hypothesis

Scientists from the University of Kansas and NASA have suggested that the initial extinctions could have been caused by a gamma ray burst originating from an exploding star within 6,000 light years of Earth (within a nearby arm of the Milky Way Galaxy). A ten-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, causing surface-dwelling organisms, including those responsible for planetary photosynthesis, to be exposed to high levels of ultraviolet radiation. This would have killed many species and caused a drop in temperatures. While plausible, there is no unambiguous evidence that such a nearby gamma ray burst has ever actually occurred.

Adrian L. Melott et al estimated that gamma ray bursts from "dangerously close" supernova explosions occur two or more times per thousand million years, and this has been proposed as the cause of the end-Ordovician extinction.

I read more than what the Wiki reports a few months ago. Analysis of Ordovician-Silurian rocks proved how, in that period, the Earth was hit by radiation.

[Rhymes]

EDIT: Frak it.  Nevermind.

[Mobius]

Stars are constantly generated. Why would the stars of the Ordovician-Silurian be any different from the stars we see today...?

[watsisname]

Mika:  Yep, that answers my question perfectly.  Thanks.

I read more than what the Wiki reports a few months ago. Analysis of Ordovician-Silurian rocks proved how, in that period, the Earth was hit by radiation.

Ooh, could I get a source to that?

[Herra Tohtori]

Stars are constantly generated. Why would the stars of the Ordovician-Silurian be any different from the stars we see today...?

Metal concentration.



The first generation of stars were mostly very large and short-lived and they only consisted of hydrogen and helium and trace amounts of lithium and beryllium (which are the four elements that were originally formed in the aftermath of the Big Bang, aka nucleosynthesis) into heavier elements (or metals, as the cosmological terminology goes - anything heavier than helium is called metal), all the way to iron. Elements heavier than iron require supernovae.

Essentially the first generation of stars had zero metal concentration. Second generation already has stuff like carbon, oxygen, silicon, sulfur, and iron and various other elements in supernovae, which show up on the later stars' spectra.

So yes, stars of different age are are somewhat different. The heaviest elements also largely sink to the core of the star, and if a star has significant amount of heavy elements to begin with, it obviously forms a heavy element core faster than a mostly "pure" hydrogen-helium star, which can affect it's life span and behaviour. Not as much as the simple size of the star dictates, but still some.

The metal concentration of protostars has much more relevance to the formation of planets around the star.


You are right, though, that in the time span from Ordovician/Silurian era to Holocene era is somewhat too short for meaningful differences to occur in the general consistency of stars visible from Earth. Half a billion year as opposed to 13.7 billion years of the universe is not really enough to discern a difference. But if you were to compare the stars born now and the stars born ca. 5 billion years ago (about when the Sun was born) there would already be some difference.

The only visible difference between 500 million years ago and now would be the positions of the stars and the amount of some giant stars with life spans of only millions of years as opposed to billions of "average" stars like Sun.

[Mobius]

True, the average metal concentration cannot change in such a limited time span. 500 million years are not that much.

Ooh, could I get a source to that?

I'd like to make it public, but I can't. The info comes from a relatively old and dedicated magazine that could be anywhere in my house.

[Liberator]

Mika, you are so smart you make this ignorant farmboy's head hurt.

[Mika]

Huh?

Firstly, my roots are not that different.

And secondly, my day job is in the field of optics. Designer, researcher, engineer, whatever necessary, it all goes.

[General Battuta]

Mika, you are so smart you make this ignorant farmboy's head hurt.

Hey, give Herra some credit.

[Black Wolf]

I read more than what the Wiki reports a few months ago. Analysis of Ordovician-Silurian rocks proved how, in that period, the Earth was hit by radiation.

I call bull****. You may have read it, but I'd go back and recheck your source. I remember my lecture on this particular even mentioning how unlikely the gamma ray hypothesis was because of the lack of physical evidence. What you mighthave read is that there was an altered oxygen isotope ratio as a result of increased UV radiation and while yes, technically this might occur as a result of a stripped ozone layer it's used in paleoclimatology to detect climate. The general idea is that as the earth cools, more water is locked up at the poles, where UV radiation is more intense, and so the Oxygen isotope ratios change (I think O13 content increases, but I'm not 100% on that). Plus, the O-S was a bimodal extinction event, a double pulse over around 10 million years, which is far more likely attributable to two phases of glaciation than a gamma ray burst that somehow had its effects felt as an separate incident 10 million years later. now, granted, 10 million years isn't super long, geologically, but it is longer than the systems that affect the biosphere would typically take to cycle things like a gamma burst.

So, yes, while the gamma burst hypothesis has a certain interest factor to it (and fits nicely with the K-T impact as an extraterrestrial mass extinction event) it really doesn't fit the evidence we do have, and there's never been much found which supports it since the publication of the paper, at least, not as far as I know.

That said, if you do find the paper you were talking about, I'd definitely like to see it. Evidence supporting a GRB for the O-S would definitely be something I'd like to see.

[Col. Fishguts]

Behold the wrath of geologists

As for the OT: The original source never mentions anything about it going supernova. But the speed at which it is contracting surely makes it worth to keep a very close eye on Betelgeuse over the next few years.

[Herra Tohtori]

I just hope it goes off in wintertime, when Orion is actually visible from here.

It would be so wrong if the southern hemisphere got that event as well as all the awesome constellations they already have there.

[Mobius]

I call bull****. You may have read it, but I'd go back and recheck your source. I remember my lecture on this particular even mentioning how unlikely the gamma ray hypothesis was because of the lack of physical evidence. What you mighthave read is that there was an altered oxygen isotope ratio as a result of increased UV radiation and while yes, technically this might occur as a result of a stripped ozone layer it's used in paleoclimatology to detect climate. The general idea is that as the earth cools, more water is locked up at the poles, where UV radiation is more intense, and so the Oxygen isotope ratios change (I think O13 content increases, but I'm not 100% on that). Plus, the O-S was a bimodal extinction event, a double pulse over around 10 million years, which is far more likely attributable to two phases of glaciation than a gamma ray burst that somehow had its effects felt as an separate incident 10 million years later. now, granted, 10 million years isn't super long, geologically, but it is longer than the systems that affect the biosphere would typically take to cycle things like a gamma burst.

So, yes, while the gamma burst hypothesis has a certain interest factor to it (and fits nicely with the K-T impact as an extraterrestrial mass extinction event) it really doesn't fit the evidence we do have, and there's never been much found which supports it since the publication of the paper, at least, not as far as I know.

That said, if you do find the paper you were talking about, I'd definitely like to see it. Evidence supporting a GRB for the O-S would definitely be something I'd like to see.

Special reply tag for you:

I did not mention any O₂ isotopes. By proof of the explosion of a supernova during that period I meant the presence of much heavier elements. We all know that, due to atom degradation, we will never, ever be able to see certain isotopes here on Earth - it doesn't mean that no isotopes of that kind ever existed here, it simply means that all isotopes (again, of that kind) no longer exist due to degradation.

So, if studies prove that a particular kind of isotopes are in rocks originated at the end of the Ordovician, we need to assume that Earth was hit by a flood of elements during that period.

It's pretty much what happened with the meteor impact that might have caused the mass extinction of the Crataceous-Paleocene - research proved how traces of iridium isotopes could be found in rocks that originated during that period.

[watsisname]

It wouldn't be that the earth was hit by a flood of heavy elements in this case.  For that to happen the event would need to be really close, within a few tens of lightyears.  I'd think if a GRB/hypernova were that close then nothing at all would have survived.  Nevermind the statistical implausibility of having one occur that close to begin with.

What you may have read is that the radiation from the event could have altered the isotopes in the rocks exposed to it, and perhaps this change was measurable.  If so I'd be interested in knowing what exacly was detected and where.

[karajorma]

So, if studies prove that a particular kind of isotopes are in rocks originated at the end of the Ordovician, we need to assume that Earth was hit by a flood of elements during that period.

You what?

How the hell is a supernova going to result in a measurable difference in the concentration of heavy elements?

[Herra Tohtori]

So, if studies prove that a particular kind of isotopes are in rocks originated at the end of the Ordovician, we need to assume that Earth was hit by a flood of elements during that period.

You what?

How the hell is a supernova going to result in a measurable difference in the concentration of heavy elements?

It doesn't.

...Well, technically there's a thing called photoneutron process which means that if a neutron is hit by a gamma ray with energy higher than the binding energy, it can be ejected from the nucleus, causing the isotope to become lighter (which can cause it to become unstable and further decay into other isotopes). There are definitely sufficiently energetic gamma rays in gamma bursts, to achieve this, but the question is would it cause detectable changes. Which is a three-fold question; first is the rate of transmutation achieved by the gamma burst, second is the stability of the isotopes made, and the third is the rarity of the isotopes in question.

If the rate of transmutation is small enough (too small amount of nuclei go through the isotopic changes), they can't be detected.
If the half-lifes of the isotopes are small enough, there's no chance to detect the rare isotopes after hundreds of millions of years.
If the isotopes happen to be common, there is really no way to tell what caused them.

All in all, I don't think there is any way to detect if such event took place based on the isotopes, similar to how asteroid or comet impacts can be detected. To introduce alien isotopes on Earth in any detectable or meaningful volume (detectable amount) requires an actual influx of the isotope (impact of some sort, which you referred to with the indium traces), or a neutron flux of significant strength... And there's no way in heaven or hell that either the heavy elements from the supernova or the neutron flux from it would ever reach Earth through several light years of space.

Nearby gamma burst would have other effects, mainly on molecular level, which could possibly be detected. Stuff like changes in crystal structures of some minerals for example... I'm going to just quote wikipedia because I don't think there's much I can add or improve on this:

A gamma-ray burst in the Milky Way, if close enough to Earth and beamed towards it, could have significant effects on the biosphere. The absorption of radiation in the atmosphere would cause photodissociation of nitrogen, generating nitric oxide that would act as a catalyst to destroy ozone. According to a 2004 study, a GRB at a distance of about a kiloparsec could destroy up to half of Earth's ozone layer; the direct UV irradiation from the burst combined with additional solar UV radiation passing through the diminished ozone layer could then have potentially significant impacts on the food chain and potentially trigger a mass extinction. The authors estimate that one such burst is expected per billion years, and hypothesize that the Ordovician-Silurian extinction event could have been the result of such a burst.

So, yeah. I don't think isotopic concentration of soil layers from different times can be used to detect gamma bursts in any meaningful accuracy. I could be wrong though, but there just seems to be too many problems with it.

[Mobius]

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[jdjtcagle]

[Mobius]

Oh, and this...

 

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[ssmit132]

  But seeing the skybox stars behind the nebula seems odd...

It's also interesting (to me) to see the HUD in Italian.