Enormous star could go supernova at any time

[David B]

As it is reported to be in its death throes.

http://news.bbc.co.uk/1/hi/sci/tech/8382348.stm

It's reported to be 4500 light years away. The Crab nebula which was visible to the naked eye in 1054 is reported to have been 6500 ly away.

It might be quite a show.

My back of envelope calculation tells me that if the bang is the same size as the Crab, then it will be just over twice as bright as the Crab was - and that was visible in daylight.

It might well make a bigger bang than the Crab, though, since the bbc report says that it is the biggest star known to science.

David

[Matty]

It is colossal. If it was sited at the centre of our Solar System, it would extend beyond the orbit of Saturn.

holy shit, thats quite the object to go bang. (or not, you know what i mean :))

I guess "at any time" in this context means sometime in the next few thousand years?

[David B]

It is colossal. If it was sited at the centre of our Solar System, it would extend beyond the orbit of Saturn.

holy shit, thats quite the object to go bang. (or not, you know what i mean :))

I guess "at any time" in this context means sometime in the next few thousand years?

I dunno.

I rather hope it's in my lifetime - I'd love to see it.

I wonder if the high energy stuff that the bang would produce would be dangerous, though. I'd have thought that it would be small compared to what comes out of the sun, but:dunno:

David

[Berthold]

Isn't Betelgeuse a likely object, too? And, it's quite luminous even now.

[Celsus]

I bet it explodes in 2012 and the Mayans were right. And stuff.

[Worldtraveller]

Would the gamma ray burst from something that size pose even a limited danger to life or electronics on earth from that range? I remember watching a documentary on the Science Channel(?) about some large star that is close enough that if it went boom, they think it could cause issues for electronics, and even destroy or damage a significant number of (mostly TV) satellites.

[Matty]

that would be fucking hilarious. As a smug bastard without TV i would laugh wholeheartedly at the civil unrest and howls of horror that would no doubt ensue were people deprived of the brain sapping dumb box for a few days.

Peopl would be lining up at the docs worried about this funny feeling they are getting, and wondering if it was a tumour or something but it would simply be pointed out that that funny feeling is their brain starting to work again.

You know the most recent study showed the AVERAGE amount of TV watched in the US per person is 32hrs per week. I was going to do a thread on it but i really havent got my head round how people watch that much, so dont really know where to start. If that trend continues than something taking out a couple dozen TV satellites might be a fucking good thing tbh.

[Berthold]

Oh, we habitual internet users can brag about not watching TV! :D

Are there any habitual TV watchers who brag about not reading dime novels?

Uh, would they know what that is? :evil:

[David B]

Would the gamma ray burst from something that size pose even a limited danger to life or electronics on earth from that range? I remember watching a documentary on the Science Channel(?) about some large star that is close enough that if it went boom, they think it could cause issues for electronics, and even destroy or damage a significant number of (mostly TV) satellites.

It might depend on whether the axis of rotation of the star is pointing at us or not, AFAIK.

The GRB is highly directional.

http://en.wikipedia.org/wiki/Gamma-ray_burst

David

[Berthold]

It would be just my luck if this happened in my lifetime and I slept through it.
Don't worry, the luminosity maximum lasts for weeks! :)

[Daynna]

You're kidding! but that's great! I was seriously worried about missing it. I should have done a little research. :)

[Jobar]

Being it's in Canis Major, we in the northern hemisphere probably wouldn't be able to see it anyway, depending on its location within the constellation.

I'd be interested to know where its spin axis points. If we're directly in line with either pole of VY CMa, we might be close enough for it to really mess us up.

[JamesBannon]

Also, keep in mind that what we are observing now actually happened 4,500 years ago. It may already have blown up. Isn't space wonderful!

[Jobar]

Some posts were split off to the thread TV viewing by country (http://www.secularcafe.org/showthread.php?t=4267).

[Sidhe747]

Andromeda is going to collide with us in 4 billion years. Now that'll be some light show!

http://apod.nasa.gov/apod/image/0807/ngc5426_gemini_big.jpg

http://www.centauri-dreams.org/wp-content/uploads/2007/05/galaxy_collision.jpg

[Eudaimonist]

Would the gamma ray burst from something that size pose even a limited danger to life or electronics on earth from that range? I remember watching a documentary on the Science Channel(?) about some large star that is close enough that if it went boom, they think it could cause issues for electronics, and even destroy or damage a significant number of (mostly TV) satellites.

Just so long as the Earth's magnetic field still protects us from the worst radiation, I think we'll be fine. Just don't be on a Mars mission at that time.


eudaimonia,

Mark

[Berthold]

Just so long as the Earth's magnetic field still protects us from the worst radiation, I think we'll be fine. Just don't be on a Mars mission at that time.


eudaimonia,

Mark
But, gamma rays aren't particles.

Except insofar as a photon is a particle. However, uncharged.

[Eudaimonist]

Just so long as the Earth's magnetic field still protects us from the worst radiation, I think we'll be fine. Just don't be on a Mars mission at that time.


eudaimonia,

Mark
But, gamma rays aren't particles.

Except insofar as a photon is a particle. However, uncharged.

Hmmm, you have a point. I suppose we have to rely on the atmosphere for that.


eudaimonia,

Mark

[Berthold]

The atmosphere is actually quite a shield. About as effective as the layer of water through which one can with impunity look at a live reactor core.

[David B]

The atmosphere is actually quite a shield. About as effective as the layer of water through which one can with impunity look at a live reactor core.

Depends what it is shielding against.

I have an old friend I've rather lost touch with who has worked on Chandra and XMM. We were talking about gamma ray bursts a few years ago, and IIRC were talking about being in the jet of a GRB a hundred (may have been a thousand) LY away.

he did some back of envelope rough approximations, that I followed him through with, and they came out with vaporising the oceans on the side of the earth facing the burst in seconds (or less).

David

[Eudaimonist]

he did some back of envelope rough approximations, that I followed him through with, and they came out with vaporising the oceans on the side of the earth facing the burst in seconds (or less).

Yes, this is precisely what I'm worried about.


eudaimonia,

Mark

[Worldtraveller]

he did some back of envelope rough approximations, that I followed him through with, and they came out with vaporising the oceans on the side of the earth facing the burst in seconds (or less).

Yes, this is precisely what I'm worried about.


eudaimonia,

Mark
I'm not worried about that, I'd just hope to be on the right side of the planet.



...wouldn't feel a thing, probably. :cool:

[Eudaimonist]

he did some back of envelope rough approximations, that I followed him through with, and they came out with vaporising the oceans on the side of the earth facing the burst in seconds (or less).

Yes, this is precisely what I'm worried about.


eudaimonia,

Mark
I'm not worried about that, I'd just hope to be on the right side of the planet.



...wouldn't feel a thing, probably. :cool:

Perhaps even the people on the other side of the planet as well. Once all that superheated steam comes round to the other side, I'm guessing we'd go out quicker than crabs dumped into hot boiling water.


eudaimonia,

Mark

[lpetrich]

One can come up with a crude estimate using the speed of sound in air:
In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s). This equates to 1,236 kilometers per hour (768 mph), or about one kilometre in three seconds and about one mile in five seconds.
It would take something like 17 hours for a sound to travel from the sub-burst point to its antipode, so we'd have plenty of time to seek shelter.

Gamma-ray bursters are very variable, but their average energy is about 1044, their average beam width is 2 to 20 degrees, and their average peak-luminosity time is around 2 seconds. According to this source (http://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/Cicerone/Cicerone_Introduction/GBM_overview.html), gamma-ray bursts have continuous spectra, with a peak around 300 keV.

-

I'll use a GRB about 1000 parsecs (3260 light-years) away as a baseline case; it's easy to scale the numbers appropriately for different distances.

That GRB will emit about 107 joules/m2, about 10,000 times the Sun's luminosity over one second.

Most of it would be gamma rays, but the visible part could still be very impressive. According to Naked eye visible GRB! | Bad Astronomy | Discover Magazine (http://blogs.discovermagazine.com/badastronomy/2008/03/20/naked-eye-visible-grb/) Using the calculations by that article's commenters, I find a visual luminosity of about 100 times the Sun's.

-

How will spacecraft survive?

From NIST: X-Ray Mass Attenuation Coefficients (http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html), the gamma rays would have a penetration depth in aluminum of about 2 cm, and in human flesh of about 5 cm. Using specific heat capacity and 1000 joules/cm2, I find that directly-exposed aluminum will be heated about 200 K, and directly-exposed human flesh about 50 K.

The radiation dose is about 200 thousand gray or 20 million rads. Using the adjustment factor Q = 1 for photons, this is 200 thousand sievert. This is too much even for the most radiation-resistant organism known, Deinococcus radiodurans.

So anyone in a spacecraft who got exposed would die in a day or so of radiation poisoning.

-

How good is the Earth's atmosphere as a radiation shield?

Most of the gamma rays will be absorbed by the upper atmosphere, which will heat it up enough to ionize it and perhaps enough to blow some of it off of the Earth entirely.

To find out how much of the atmosphere gets heated, we find out how far down the gamma rays penetrate, and for that, we can use Basic Physics of Nuclear Medicine/Attenuation of Gamma-Rays - Wikibooks, collection of open-content textbooks (http://en.wikibooks.org/wiki/Basic_Physics_of_Nuclear_Medicine/Attenuation_of_Gamma-Rays) and NIST: X-Ray Mass Attenuation Coefficients - Air, Dry (http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/air.html).

In average sea-level air, the coefficient is about 0.00016 cm-1 or an e-folding distance of about 60 m. The density of this air is about 0.0012 times that of water, and if the Earth's atmosphere was squashed down to that density, it would have a height of about 10 km.

This gives the Earth's atmosphere a gamma-ray optical depth of about 160. Though this number looks small, it means that only about 10-70 of the GRB's gamma rays will make it to the surface -- and that's for the GRB being overhead.

For 20-MeV gamma rays, the coefficient goes down by a factor of 10, giving about 600 m of e-folding distance. That nevertheless yields an optical depth of 16, which means that most of the higher-energy gamma rays will still be absorbed.

-

What will happen to the exposed part of the atmosphere?

The gamma rays will have an average penetration depth of where the pressure reaches about 1/160 the sea-level pressure, or 6 millibars. Using the Standard Atmosphere Calculator (http://www.digitaldutch.com/atmoscalc/), I find an altitude of about 35 km.

This is in the middle of the stratosphere, well above where most airliners cruise. BTW, airliners won't directly receive the GRB's gamma-ray flux, because 1/4 to 1/3 of the Earth's atmosphere will still be above them.

The specific heat of dry air at constant pressure is about 1.006 J/g/K, meaning that the upper atmosphere will be heated about 140 K.

This is not enough to ionize it, so the flash of visible light will get through. Anyone looking at the source at the time on a clear day may get a blind spot at the GRB's image on the retina.

[Jobar]

Loren, wouldn't each individual gamma ray ionize any atoms they hit? While the total energy imparted to the upper atmosphere may mean that it won't be converted into a plasma, I would think that the number of ionized particles would be very large. How that energy would affect the surface, I have no idea, but I feel sure at least all our electronics would be fried for good and all.

[lpetrich]

That would indeed be the case, though the ionization fraction is not likely to be high in my baseline case. The air would have to get heated few thousand degrees to ionize most of its molecules.

But it would likely produce a bright aurora.

Another effect of a big gamma-ray flash is an electromagnetic pulse, discovered in nuclear-bomb tests like Starfish Prime. That bomb was detonated at an altitude of 400 km, and its energy output was 1.4 megatons, with 0.1% of it in gamma rays. The energy in its gamma rays was thus 1.4 kilotons. It fried a lot of electronics in Hawaii, and it produced an aurora that lasted for a few minutes.

My baseline GRB is equivalent to releasing about 5000 megatons of gamma-ray energy at 400 km altitude, and that's well off the scale of Wikipedia's graph of EMP electric-field strength. An extremely rough extrapolation from that graph suggests a strength of about 100 thousand volts/m.

Anything electrical without a good surge suppressor would be fried.

-

The Starfish Prime aurora lasted about 7 minutes, and a GRB aurora would likely last a similar length, because it would dissipate in the same way. If most of the arriving GRB's energy went into the aurora, it would have a brightness of about 50 times the Sun's. Even if that is a great overestimate, its aurora would still be very bright.

-

The GRB would also add to the Van Allen radiation belts, which could be enough to knock out whichever satellites survived the GRB itself.

To compare to where radiation-hardened spacecraft have successfully operated, we compare to the environment around Jupiter's moons (this page of course notes ([url=http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt)):
Satellite | Dose (sievert/day)
Callisto | 0.0001
Ganymede | 0.08
Europa | 5.4
Io | 36
Thebe | 180

For the Earth's radiation belts, it is about 25 sievert/year.

So this baseline GRB would deliver what a spacecraft at Io would record over 10 years(!)

[Berthold]

Anyway: In order to have a high intensity at great distance, a beam has to be narrow. Considering the emptiness of space, what's the chance of a beam to hit anything with catastrophic intensity?

[Jobar]

There's an excellent science fiction novel, Diaspora by Greg Egan, which describes a gamma-ray burst from two colliding neutron stars at a hundred light-years' distance, and the effect this would have on the Earth. It would destroy the ozone layer completely, and produce gigatons of nitrogen oxides, which would eventually reach the surface as acid rain; Egan's story posited the extinction of all surface life, from those two effects. The energy imparted to the Earth's atmosphere was on the order of a billion terajoules, which I'm sure is far more than the VY CMa supernova could strike us with, even if we were directly in line with one pole- but still, it might do us far more damage than even a large asteroid impact.

For those of you who enjoy sf, I can't praise Egan's novel highly enough; the extinction of all Earth's megafauna is just the beginning of the story!

[Loren Pechtel]

Another effect of a big gamma-ray flash is an electromagnetic pulse, discovered in nuclear-bomb tests like Starfish Prime. That bomb was detonated at an altitude of 400 km, and its energy output was 1.4 megatons, with 0.1% of it in gamma rays. The energy in its gamma rays was thus 1.4 kilotons. It fried a lot of electronics in Hawaii, and it produced an aurora that lasted for a few minutes.

My baseline GRB is equivalent to releasing about 5000 megatons of gamma-ray energy at 400 km altitude, and that's well off the scale of Wikipedia's graph of EMP electric-field strength. An extremely rough extrapolation from that graph suggests a strength of about 100 thousand volts/m.

Anything electrical without a good surge suppressor would be fried.

I doubt civilization would survive this.

[lpetrich]

That's not difficult to calculate; you only need some simple algebra and geometry. You'll need the size of the object and its number density -- and those of objects that are likely to get in the way.

Turning to gamma-ray burst progenitors, the long ones are likely from the collapse of very massive stars, and the short ones are possibly mergers of neutron stars or giant flares on magnetars (highly-magnetic pulsars).

About the first one:
Three very special conditions are required for a star to evolve all the way to a gamma-ray burst under this theory: the star must be very massive (probably at least 40 Solar masses on the main sequence) to form a central black hole in the first place, the star must be rapidly rotating to develop an accretion torus capable of launching jets, and the star must have low metallicity in order to strip off its hydrogen envelope so the jets can reach the surface. As a result, gamma-ray bursts are far rarer than ordinary core-collapse supernovae, which only require that the star be massive enough to fuse all the way to iron.
This rules out most of the nearby supergiants, since they still have their hydrogen envelopes, and are likely not massive enough. So we have to look among Wolf-Rayet stars, which have blown them off.

The closest Wolf-Rayet star is a star in the Gamma Velorum system, about 800 light-years / 260 parsecs away.

Eta Carinae itself is a luminous blue variable, an intermediate between hydrogen-rich and hydrogen-poor WN Wolf-Rayet stars, so it fits. its distance is about 7500 ly / 2300 pc.

[Mung Dynasty]

This rules out most of the nearby supergiants, since they still have their hydrogen envelopes, and are likely not massive enough. So we have to look among Wolf-Rayet stars, which have blown them off.

The closest Wolf-Rayet star is a star in the Gamma Velorum system, about 800 light-years / 260 parsecs away.Which is only one quarter the distance you were using for your calcs, which means the energy that hit us from a GRB at that distance would be sixteen times higher than your calcs. :D

[lpetrich]

Yes.

On the Earth's surface, the only primary effects we'd experience would be from the visible light and nearby IR and UV; the gamma rays would be stopped in the upper atmosphere. Here's a rough guide to how good a shield our atmosphere is:

Like:

30 ft / 10 m of water
10 ft / 3 m of rock
3 ft / 1 m of lead

Wood and plastic and the like are comparable to water, being composed of similar light elements.

Concrete and brick and cinderblock and the like are artificial rock and have similar stopping power.

But secondary effects are another story entirely. I've already mentioned EMP's and bright auroras.

I found an article on the effects of GRB's, NASA - Explosions in Space May Have Initiated Ancient Extinction on Earth (http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html)

Evaluating the effects of one about 6000 lyr / 2000 pc away, Dr. Adrian Melott and Brian Thomas considered what would happen to the Earth's upper atmosphere. Most of the Earth's ozone layer is between about 20 and 40 km up, and that's around the average penetration depth of the GRB's gamma rays.

The gamma rays will split nitrogen molecules as well as oxygen ones, and the stray nitrogen atoms will combine with oxygen molecules to make nitrogen oxides, which will react with atmospheric ozone.

They estimate that this effect will destroy about half the atmospheric ozone in a few weeks, and that the atmosphere will only slowly recover, getting back to 90% original in 5 years.

This would let in enough of the Sun's more energetic ultraviolet light to be devastating to photosynthesizing organisms; it could cause a mass extinction.

CJO - Abstract - Did a gamma-ray burst initiate the late Ordovician mass extinction? (http://journals.cambridge.org/action/displayAbstract;jsessionid=1C5F2761949DF806C1F90DC BF6D1A6BC.tomcat1?fromPage=online&aid=240775)

Gamma-ray bursts (GRBs) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average two or more times per billion years. At least five times in the history of life, the Earth has experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRBs may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. A special feature of GRBs in terms of terrestrial effects is a nearly impulsive energy input of the order of 10 s. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.

This is the Ordovician–Silurian extinction event

The main problem with the GRB hypothesis is the failure to find any traces in the rocks of anything that can plausibly be interpreted as being specifically caused by a GRB. Nothing like the K-T iridium layer, which implies that something or other had spewed or blasted a lot of iridium-containing dust into the air at the exact time of that extinction. However, we may not know what to look for, and someone may find some geochemical clue for recognizing (say) increased solar UV.

[Matty]

smart motherfuckers itt ^^ :)

[Eudaimonist]

Anything electrical without a good surge suppressor would be fried.

I doubt civilization would survive this.

I'll bet civilization would survive this. It's not like we are slouches at mass producing electronics.


eudaimonia,

Mark

[David B]

Anything electrical without a good surge suppressor would be fried.

I doubt civilization would survive this.

I'll bet it would. It's not like we are slouches at mass producing electronics.


eudaimonia,

Mark

We are slouches at producing very much at all if we haven't got any electricity.

David

[Eudaimonist]

We are slouches at producing very much at all if we haven't got any electricity.

We are clever beings. We will find ways to restore electricity and recover.

I'm assuming here that EMP is the only trouble we have. If UV light is killing off plantlife, that's much more difficult to recover from.


eudaimonia,

Mark

[David B]

We are slouches at producing very much at all if we haven't got any electricity.

We are clever beings. We will find ways to restore electricity and recover.

There is time to consider, bearing in mind that petrol pumps and water supply is dependent on electricity. I don't like to think about what it would be like to be in a big city like NY without electricity for even a week in deep winter or high summer without electricity. Because it also means without water.

I'm assuming here that EMP is the only trouble we have. If UV light is killing off plantlife, that's much more difficult to recover from.


eudaimonia,

That is a potential problem, too.

David

Mark[/QUOTE]

[Loren Pechtel]

Anything electrical without a good surge suppressor would be fried.

I doubt civilization would survive this.

I'll bet civilization would survive this. It's not like we are slouches at mass producing electronics.


eudaimonia,

Mark

Mass produce electronics with what? All the production equipment itself is electronic. Not to mention that virtually every heavy hauling device is also kaput. Not to mention all long range communications.

Sure, in time we could recover from this if that were the only problem, but it wouldn't be. What happens when the food rots in the field (the harvesting machinery is dead) while the cities starve (even if it were harvested there would be no way to get it to the cities.)

[Jobar]

There's a large difference between the destruction of technological civilization and actual extinction of humanity. I rather doubt that even in the worst possible case, the VY CMa supernova could render us extinct. However, it's not impossible it could severely damage or even destroy modern civilization.

[Berthold]

The idea of people fighting over blackberries and beechnuts is not specially appealing. :eek:

Just what population density could survive if people worked the land manually in family groups? Not much leeway for culture and science in this scenario.

[lpetrich]

It's unlikely that VY CMa will make a gamma-ray burst anytime soon. It's not a Wolf-Rayet star but a red supergiant; it still has its outer layers of hydrogen. But if it blows off its outer layers before becoming a supernova, it will become one.

Supernovae (http://hyperphysics.phy-astr.gsu.edu/HBASE/astro/snovcn.html) have maximum luminosities of as much as 1010 the Sun's.

Here are the various types of supernovae:

Type Ia - white-dwarf collapse
Type II - core collapse of supergiant with hydrogen and helium envelopes
Type Ib - core collapse of supergiant with helium envelope (no hydrogen)
Type Ic - core collapse of supergiant with neither (no hydrogen or helium)

Type 1a supernovae go up to about 5*109 solar luminosities with relatively little variation; the others are more variable. Types 1b and 1c are relatively rare, meaning that they are produced only by very massive stars; Type 1c is likely associated with gamma-ray bursts.

But even at 1010 solar luminosities, a supernova would have to be half a parsec (1.6 light years) away to have the apparent brightness of the Sun.

If nearby supergiants Rigel, Betelgeuse, or Antares became supernovae, they wouldget apparent magnitude -15, about 10 times brighter than the full Moon. Most of their luminosity would be in the ultraviolet, however, making their apparent visual magnitude perhaps -10 or so. This is about 10-4 the Sun's ultraviolet luminosity, so they would not pose a threat to the ozone layer.

VY CMa is about 8 times farther away, and it would therefore pose even less of a threat.

They would most likely become supernovae before they blow off their outer layers, thus becoming Type II supernovae instead of Type Ib or Ic. Rigel is currently a blue supergiant, and it would become a red supergiant before it exploded. Betelgeuse and Antares are already red supergiants, and they are almost half the size of VY CMa.

[lpetrich]

I researched this question further, and while much of a Type I supernova's light is likely emitted as ultraviolet, because they started emitting much of their light in the ultraviolet, that is not necessarily true of a Type II supernova.

I crunched some of the numbers in List of supernovae, and the brighter ones reach about 109 solar luminosities around peak luminosity. I'd compared that figure to the previous maximum of 1010 L(Sun) and concluded that the missing light is likely ultraviolet.

But I decided to investigate this question further to see if I could get better numbers, like photosphere-temperature values. I have succeeded, and I've concluded that a Type II supernova glows in the ultraviolet for only a little bit of its expansion.

Type II supernovae are sometimes used to measure distances to galaxies, by using the Expanding Photosphere Method. A supernova's photosphere expands, of course, and that expansion can be put to work for determining its distance. One gets a linear velocity of expansion by noticing that different parts of it move toward us at different rates, broadening the spectral lines. One gets an angular velocity of expansion by finding the angular diameter as a function of time by using its temperature and luminosity.

When it can be compared to other methods, this method gives reasonably good results.

From The Expanding Photosphere Method (EPM) of measuring distances (http://spiff.rit.edu/classes/phys440/lectures/epm/epm.html):

When the core collapses, it creates a shock wave that travels outward, heating its outer envelope to 100,000 K or so and pushing it outward with a velocity of 5,000 to 10,000 km/s.

The supernova thus makes a big flash of ultraviolet light, since the peak emission wavelength is 30 nm, well into the ultraviolet. But it cools until it reaches a point where the electrons combine with hydrogen ions, making the material more transparent. This produces an effective photosphere temperature of around 5,000 K for the next few months at least. It is a little bit cooler than the Sun's photosphere; its peak is 600 nm, well within the visible.

The author of that page quoted some fancier calculations on various supernovae, like for 1970G a decline from 10,000 K at day 35 to 5,000 K at day 70.

-

What does that mean for the Earth? That a Betelgeuse or Antares supernova would be ultraviolet-hot only briefly, for at most a few days or so. Even that, however, could cause ozone-layer damage if the supernova was close enough, because of the very high emission temperature. But neither Betelgeuse nor Antares are close enough to be troublesome.

[Loren Pechtel]

There's a large difference between the destruction of technological civilization and actual extinction of humanity. I rather doubt that even in the worst possible case, the VY CMa supernova could render us extinct. However, it's not impossible it could severely damage or even destroy modern civilization.

But it's only our brains that set us apart from the animals--if we fall our prime advantage is pretty much neutralized.

[Loren Pechtel]

The idea of people fighting over blackberries and beechnuts is not specially appealing. :eek:

Just what population density could survive if people worked the land manually in family groups? Not much leeway for culture and science in this scenario.

No modern fertilizers = *FAR* lower crop yields. The vast majority of the population dies.

[Jobar]

I had thought that an exploding supernova's magnetic field channeled a very powerful gamma-ray burst along its axis, and the "worst case" I was thinking of would be if we were unlucky enough to be exactly in line with that axis. I understand why a supernova which still has some hydrogen or helium in its outer layer wouldn't produce a gamma burst, because that layer would absorb the gamma rays and only allow ultraviolet to pass through.

I really, really would like to know which way VY CMa's axis is pointing!

[JamesBannon]

I'm not bothered. If it happens, it happens. It's not like there's a great deal we can do about it anyway. It may already have happened for all we know.

[Jobar]

It would depend on how much lead time we had, how certain we were about it, and on how much radiation we would get. If we knew for a fact that in ten years we'd experience a few hours or days of intensive gamma irradiation, I think a fair lot *might* be done. There's a lot we could do to protect things like vital electronics, power transmission systems, and military assets, if we knew we definitely faced such a danger.

[JamesBannon]

It would depend on how much lead time we had, how certain we were about it, and on how much radiation we would get. If we knew for a fact that in ten years we'd experience a few hours or days of intensive gamma irradiation, I think a fair lot *might* be done. There's a lot we could do to protect things like vital electronics, power transmission systems, and military assets, if we knew we definitely faced such a danger.

But, we can't tell if the star has blown up until the "light" reaches us. So, an instrument on earth wouldn't get any lead time simply by watching the star. What we are observing now is the state of the star at roughly the time the Romans left Britain. It may have gone supernova shortly after that, say 100 years, and we wouldn't have the faintest clue.

[lpetrich]

I had thought that an exploding supernova's magnetic field channeled a very powerful gamma-ray burst along its axis,
Ultimately the star's rotation, which would flatten out the star as it collapses and make it easiest for the gamma rays to escape from its poles.

and the "worst case" I was thinking of would be if we were unlucky enough to be exactly in line with that axis.
That's essentially it.

I understand why a supernova which still has some hydrogen or helium in its outer layer wouldn't produce a gamma burst, because that layer would absorb the gamma rays and only allow ultraviolet to pass through.
You got it right. Observed gamma-ray bursts are very rare, consistent with their usually being blocked by a star's outer layers. Only very massive stars blow off enough material to let GRB's through.

I really, really would like to know which way VY CMa's axis is pointing!
It may be possible to observe VY CMa with some telescopes set up to do interferometry. It's already possible to do this with Betelgeuse, and it's been possible to observe starspots on its surface. But since Betelgeuse is nearly 10 times closer and half the size, VY CMa will have 1/5 Betelgeuse's angular size.

Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of alpha Orionis (http://adsabs.harvard.edu/abs/1998AJ....116.2501U)
Spatially Resolved HST Spectra of alpha Orionis' Chromosphere (http://adsabs.harvard.edu/abs/1996AAS...188.7106U)

Betelgeuse's spin axis is tilted about 20 degrees to the line of sight, and its rotation period is about 17 years. Its size is about 4 AU's, nearly as big as Jupiter's orbit, and it does not have a very well-defined surface.

I can't find anything comparable for Antares, however.

-

Here is where to find them in the sky. They both have high apparent brightness, so they should be easy to find, even in suburban or urban areas.

Antares (Alpha Scorpii) is near the southern horizon at mid-northern latitudes in northern-hemisphere summer. In Australia and New Zealand, it will be high in the sky.

Betelgeuse (Alpha Orionis) is at the upper right corner of the Orion stars, and is easily visible southward in northern-hemisphere fall and winter.

So all you people, go out and look at the stars and see if you can find Betelgeuse.

[Jobar]

It would depend on how much lead time we had, how certain we were about it, and on how much radiation we would get. If we knew for a fact that in ten years we'd experience a few hours or days of intensive gamma irradiation, I think a fair lot *might* be done. There's a lot we could do to protect things like vital electronics, power transmission systems, and military assets, if we knew we definitely faced such a danger.

But, we can't tell if the star has blown up until the "light" reaches us. So, an instrument on earth wouldn't get any lead time simply by watching the star. What we are observing now is the state of the star at roughly the time the Romans left Britain. It may have gone supernova shortly after that, say 100 years, and we wouldn't have the faintest clue.

I'm not sure if there are any detectable events which might give us warning that the star's gone supernova, but it's possible that such events exist, and that we might realize them as such. We just don't know, at this point. If the core collapse takes place in a matter of seconds- entirely possible- we'd get little to no warning. But there may be preliminary 'sputterings' as the core temperature rises, and different fusion chains start synthesizing different elements below iron. I'm sure that we'll find out some fascinating things by watching the coming events- even though this star's "death throes" still might outlast us all, and might even outlast human civilization!

[David B]

It would depend on how much lead time we had, how certain we were about it, and on how much radiation we would get. If we knew for a fact that in ten years we'd experience a few hours or days of intensive gamma irradiation, I think a fair lot *might* be done. There's a lot we could do to protect things like vital electronics, power transmission systems, and military assets, if we knew we definitely faced such a danger.

But, we can't tell if the star has blown up until the "light" reaches us. So, an instrument on earth wouldn't get any lead time simply by watching the star. What we are observing now is the state of the star at roughly the time the Romans left Britain. It may have gone supernova shortly after that, say 100 years, and we wouldn't have the faintest clue.

I'm not sure if there are any detectable events which might give us warning that the star's gone supernova, but it's possible that such events exist, and that we might realize them as such. We just don't know, at this point. If the core collapse takes place in a matter of seconds- entirely possible- we'd get little to no warning. But there may be preliminary 'sputterings' as the core temperature rises, and different fusion chains start synthesizing different elements below iron. I'm sure that we'll find out some fascinating things by watching the coming events- even though this star's "death throes" still might outlast us all, and might even outlast human civilization!

A bit like predicting the exact time a volcano blows catastrophically, I'd have thought. Insofar as there is physics involved in the blow, but not enough have been closely observed to give us good predictions from the precursors we see.

With volcanoes there are very few big eruptions that have been closely monitored. St Helens, Pinatubo, maybe a couple more. That one that was pretty closely predicted that cause the disastrous lahar that killed lots of people because the warnings weren't precise enough.

With objects like this - it's the first time AFAIK that something has been observed that is showing signs of precursors to something big happening.

Who knows? Maybe the real experts in cosmology have ideas:dunno:

David

[lpetrich]

The starts of earlier phases of nucleosynthesis produce noticeable hiccups in the star's outer layers, though the starts of later phases may not. I'd have to hunt through http://adsabs.harvard.edu to see if anyone has addressed this question.

In any case, it's in some ways easier to model stars than to model volcanoes. One can use the approximation of spherical symmetry in most cases, with some kludgy way of handling turbulence; that reduces the problem's space dimensions from 3 to 1. Likewise, much of the physics is relatively straightforward to calculate from first principles, like the equation of state and radiative transfer; the same cannot be said of most volcano materials. However, one can do much of that empirically, the way one handles nuclear reaction rates in stars.


When the star's core runs out of hydrogen, it slowly collapses until it start hydrogen burning outside of it. The outer layers then bloat up, producing the red giant / supergiant stage.

When it gets compressed and hot enough, at something like 170 million K, it will start burning helium to carbon and oxygen.

The Sun will only get this far before it blows off its outer layers and becomes a white dwarf, but massive stars will go further. Their cores' elements will get burned to successively more massive ones, ending in iron, while these reactions will continue outside the core, making layers of reactions.

Nucleosynthesis - The Physics Hypertextbook (http://physics.info/nucleosynthesis/), Type II supernova (25-solar-mass star)
Fuel | Products | Time | Temperature (K) | Density (g/cm3)
H | He | 10 million years | 7*107 | 10
He | C, O | 1 million years | 2*108 | 2*103
C | Ne, Na, Mg, Al | 1 thousand years | 8*108 | 106
Ne | O, Mg | 3 years | 1.6*109 | 107
O | Si, S, Ar, Ca | 0.3 years | 1.8*109 | 107
Si | Ni, Fe | 5 days | 2.5*109 | 108


As these reactions continue, the core gradually shrinks to the size of a white dwarf, about that of Earth.

Iron-56 cannot react any further, so it accumulates, and when about 1.44 solar masses or so accumulate, it collapses under its own weight, taking about a second to do so.

If it does not become a black hole, as it might for a very massive star, it bounces in about a millisecond, and this bounce and various other effects create a shock wave in the outer core that proceeds outward and makes the supernova.

It has a temperature of 1011 K, and releases about 1046 joules of neutrinos, because those are the only particles it can produce that will escape. This is about 100 times the energy that the Sun will release over its entire lifetime.

SN 1987A was a core-collapse supernova about 168 thousand light-years / 52 thousand parsecs away in the Large Magellanic Cloud. Three neutrino observatories detected a total of 24 neutrinos from it emitted in less than 13 seconds. They were emitted about 3 hours before that supernova was observed in the visible.

Its progenitor star, Sanduleak -69° 202a, was a Luminous Blue Variable, much like Eta Carinae. Scaling to the size of Betelgeuse, Antares, and VY CMa, the shock front would take about a day to get out of the star.


These three stars' supernova neutrinos would be easy to observe. Scaling from SN 1987A, I predict about 104 for VY CMa and 106 for Betelgeuse and Antares.

[lpetrich]

I'll take a break from supernovae and turn to surviving without electricity.

Surprising as it may seem, electricity-based technology is remarkably recent. The more industralized places only started getting electrified over the late 19th and early 20th centuries. So without electricity, we could get as far as a Victorian / steampunk world.

A timeline of notable developments:

1744-1746: Ewald Georg von Kleist and Pieter van Musschenbroek invent the Leyden Jar for storing static electricity; it is the first capacitor.
1780: Luigi Galvani invents the Galvanic Cell, the first electric battery.
1800: Alessandro Volta invents a stack of galvanic cells, the Voltaic Pile. Connecting in series increases the total voltage.
1802: Sir Humphry Davy constructs the first electric light, a strip of platinum heated until it glowed.
1821: Michael Faraday constructs the first electric motor, a toy design.
1825: William Sturgeon invents the electromagnet.
1831: Michael Faraday invents the first electric generator, a homopolar one (low voltage, but can make high current).
1831: Hippolyte Pixii builds the first dynamo, a more practical design.
1830: William Sturgeon invents the first practical electric motor.
1835: Joseph Henry invents the electrical relay, an electromechanical switch.
1837: Sir William Fothergill Cooke, Charles Wheatstone, Samuel Morse and Alfred Vail develop commercial telegraph services.
1840: Warren De La Rue encloses a platinum filament in a vacuum tube to protect it, making the first light bulb.
1866: Transatlantic telegraph cable laid.
1873: Joseph Wilson Swan invents a carbon-fiber-filament light bulb, thus avoiding platinum's expense.
1875: Alexander Graham Bell, among others, invents the telephone.
1876: Tivadar Puskas invents the telephone switchboard.
1880: Thomas Alva Edison invents a long-lasting light bulb.
1881: First electric rail vehicles go into service near Berlin, Germany.
1882: Thomas Alva Edison creates first electricity-distribution network, for Lower Manhattan (110 volts direct current).
1887: Nikola Tesla does a lot of work on alternating current, gets several patents, and starts a "War of the Currents". Alternating current eventually wins.
1888: Heinrich Hertz demonstrates transmission and detection of radio waves.
1888: Hermann Hollerith invents an electric tabulating machine, a predecessor of computers. His company eventually becomes IBM.
1891: Almon Strowger invents the first automatic telephone switchboard.
1896: Alexander Popov and Guglielmo Marconi do the first radio broadcasts.
1904: John Fleming invents the vacuum-tube diode, an electronic one-way valve.
1906: Robert von Lieben and Lee De Forest invent the vacuum-tube triode, an electronic switch and amplifier.
1906: Reginald Fessenden does first voice radio broadcast.
1910: William David Coolidge invents a tungsten-filament light bulb.
1920: First commercial radio-station broadcasts of news and entertainment.
1926: Electric recording and playing of gramophone/phonograph records becomes practical.
1927: Philo Farnsworth demonstrates the first working television system.
1928: Fritz Pfleumer invents magnetic tape.
1929: First TV broadcasts, in Germany.
1935: Émile Girardeau, Dr. Robert M. Page, and P.K.Oschepkov invent radar.
1936: Paul Eisler invents printed circuits, which greatly simplify manufacturing of electronic devices.
1946: ENIAC, the first all-electronic general-purpose computer.
1947: John Bardeen, Walter Brattain, William Shockley construct the first transistors (solid-state electronic switches).
1948: The Manchester Machine, the first stored-program computer.
1951: The Remington Rand UNIVAC, the first mass-produced computer
1955: First commercial transistorized computers.
1956: The Regency TR-1, the world's first commercial transistor radio.
1958: Jack Kilby builds the first integrated circuit; transistors and other components built with printed-circuit techniques. His successors build integrated-circuit chips with increasing numbers of transistors, up to several billion nowadays.
1964: IBM introduces its System/360 family, with a shared CPU architecture; programs written for one of them can run on another of them. It becomes the first of several such families, like the Intel 80x86 family.
1965: First integrated-circuit computers, for the Minuteman II missile.
1965: Intelsat 1, the first communications satellite, launched.
1969: First routers for a peer-to-peer network, the IMP's for a predecessor of the Internet.
1971: The Intel 4004, the first microprocessor (CPU chip). Its successors have replaced older, discrete-component CPU designs while acquiring the capabilities of those designs.
1975: The MITS Altair 8800, the first home computer. We are all using its successors.

[Eudaimonist]

Mass produce electronics with what? All the production equipment itself is electronic. Not to mention that virtually every heavy hauling device is also kaput. Not to mention all long range communications.

You're off my world survival team! A little constructive optimism, please. :)

Assuming that all electronic equipment was fried (and I don't think we should assume this), we might need to quickly use mechanical means to restore power and assemble at least simple electronic equipment. Even in our computerized age, we haven't forgotten how to use transistors and copper wiring.

Yes, it might require a few "stages" of technological development, but with a lot of hussle I think we could get back on our feet before too much of that starvation occurs to render the project moot.

Chalk my view up to optimism, if you choose. I see no need for dire pessimism.


eudaimonia,

Mark

[Eudaimonist]

[Here is where to find them in the sky. They both have high apparent brightness, so they should be easy to find, even in suburban or urban areas.

Antares (Alpha Scorpii) is near the southern horizon at mid-northern latitudes in northern-hemisphere summer. In Australia and New Zealand, it will be high in the sky.

Betelgeuse (Alpha Orionis) is at the upper right corner of the Orion stars, and is easily visible southward in northern-hemisphere fall and winter.

So all you people, go out and look at the stars and see if you can find Betelgeuse.

I love to see these stars in twilight because I can see their redness much more clearly.

Still, it would be fun to see one of them go nova assuming that it would be safe for us here on Earth. That would be an amazing sight.


eudaimonia,

Mark

[Berthold]

So all you people, go out and look at the stars and see if you can find Betelgeuse.
Orion is one of the few constellations that I readily find when it's up. ;)

[Jobar]

Black powder and alcohol
When the states and the cities fall.
When your back is against the wall,
Black powder and alcohol.

Give me charcoal to the measure two.
Send the bullet where you want it to.
Give me sulfer to the measure three.
Make that powder gonna keep you free.
Give me salt peter, measure fifteen.
Sweetest shootin' that you've ever seen.

Gimme water, yeast, and veggie trash.
Leave it sittin' in a slurry mash.
When it's ready, put it in the still.
If you can't heat it then the sunlight will.
Draw the alcohol away, and then
Ya put the slurry back and start again.

Booze will clean your cuts or run your car.
You can make it anywhere you are.
Black powder in your cartridge shell
Will send the robbers runnin' clean to hell.
You can make 'em if you just know how,
So kids, remember what I'm tellin' you now.

Black powder and alcohol
When the states and the cities fall.
When your back is against the wall,
Black powder and alcohol!

Yah

:D

[Loren Pechtel]

Mass produce electronics with what? All the production equipment itself is electronic. Not to mention that virtually every heavy hauling device is also kaput. Not to mention all long range communications.

You're off my world survival team! A little constructive optimism, please. :)

Assuming that all electronic equipment was fried (and I don't think we should assume this), we might need to quickly use mechanical means to restore power and assemble at least simple electronic equipment. Even in our computerized age, we haven't forgotten how to use transistors and copper wiring.

Yes, it might require a few "stages" of technological development, but with a lot of hussle I think we could get back on our feet before too much of that starvation occurs to render the project moot.

Chalk my view up to optimism, if you choose. I see no need for dire pessimism.


eudaimonia,

Mark

"Restore" power?? Good luck putting those generators back online! Their controls have had it, there's no way to run them safely.

I do believe we could in time recover from this if it were the only problem--but when people are fighting over the food they aren't going to be rebuilding the technology. I also expect the guys who are best able to rebuild won't survive the food wars.

[JamesBannon]

They were emitted about 3 hours before that supernova was observed in the visible.

Let's call those neutrinos the "advanced guard". Detecting them means we have approximately 3 hours before the "main force" strikes. That's not an awful lot of time. By the time anyone gets to hear of it, the main force will have arrived and scorched us, assuming that is what will happen.

[lpetrich]

From my timeline of electricity-based technologies, one can see a progression toward smaller-scale and more vulnerable systems:

Electromechanical
Vacuum tubes
Discrete transistors
Integrated circuits

the latter with rapidly shrinking component size. Computer-chip transistors are nowadays often around 1 micron in size, about the size of a bacterium.

On the subject of surviving a GRB's electromagnetic pulse, one can study the literature on EMP effects to get an idea of what's likely to survive and what's not. Like


The effects of nuclear weapons: debunking lying exaggerations that encourage proliferation: EMP radiation from nuclear space bursts in 1962 (http://glasstone.blogspot.com/2006/03/emp-radiation-from-nuclear-space.html)
Electromagnetic Pulse - Nuclear EMP - futurescience.com (http://www.futurescience.com/emp.html)
Electromagnetic Pulse - Soviet Test 184 - EMP (http://www.futurescience.com/emp/test184.html)
Electromagnetic Pulse Protection - EMP - Futurescience.com (http://www.futurescience.com/emp/emp-protection.html)
Notes about Electromagnetic Pulse - EMP- Futurescience.com (http://www.futurescience.com/emp/emp-notes.html)


Anything in a Faraday Cage and with good power-supply protection will very likely survive. Many server farms and data centers have uninterruptible power supplies and other sorts of protection against power-supply problems, but I don't know how "caged" they typically are.

However, electricity-transmission and communication infrastructure is likely to be very vulnerable, and vehicle electronics is also likely to be vulnerable. The avionics of airliners, for instance; many recent airliners are fly-by-wire. Car ignitions may also be vulnerable.

I don't know if anyone has done any systematic study of GRB EMP effects, however.

[David B]

They were emitted about 3 hours before that supernova was observed in the visible.

Let's call those neutrinos the "advanced guard". Detecting them means we have approximately 3 hours before the "main force" strikes. That's not an awful lot of time. By the time anyone gets to hear of it, the main force will have arrived and scorched us, assuming that is what will happen.

If this was taken seriously and prepared for, it would give an hour to verify that we were in deep shite, another hour to broadcast on every channel, and get the cops going through the streets with loudspeakers, that people should switch everything off, and pull all the plugs. And another hour for the people running the power system to switch off and get as much as possible isolated from everything else.

Even if it means blowing down power lines. Isolating things is good.

At least, that is the impression I got looking at some documentrary about what the sun could potentially do at the worst of its cycle.

David

[JamesBannon]

That is, assuming the lead time is 3 hours. Intuitively, one would expect the lead time to vary with where the supernova is and what kind it is.

[David B]

That is, assuming the lead time is 3 hours. Intuitively, one would expect the lead time to vary with where the supernova is and what kind it is.

The more pressing question, statistically, would seem to be getting some sort of response to abnormalities from the sun.

Get them in place, and understand the process of going supernova and its precursors better, then slotting supernova warnings in wouldn't seem much of a problem.

A few years ago solar activity came close to seriously damaging the Canadian grid, I understand. Now things in the electrical infrastructure are much closely connected, on the one hand, and the blip of the sun's activity that caused it was big, but nowhere near as big as worst case.

According to the very plausible documentary I watched - though I can't remember what it was called or on what channel - this is something that seriously needs addressing.

David

[Jobar]

I agree that a huge solar flare and CMA (coronal mass ejection) is a much more serious danger to our power transmission systems, and that anything which would help deal with that would also be just the sorts of things that would protect us from any potential supernova (that wasn't so close it would fry us in a way similar to Greg Egan's tale, which I mentioned in post #28.)

Loren, you mentioned the 3-hour difference between the arrival of SN1987A's neutrinos, and its photons. That neutrino burst, generated at the moment of core collapse, escaped the star at lightspeed. The neutrinos that heat the star and actually cause the supernova explosion are converted into gamma photons, which then must 'percolate' through the exploding matter of the star. So, I'm thinking that 3 hours should be pretty much constant for most supernovas- except the ones which have blown off most of their outer layers and have formed a neutron star which then absorbs enough matter to trigger collapse to a black hole.

More mass in the outer layers would mean a somewhat longer interval, less mass a shorter one. But still, we'd always see the neutrino wave before we see the photons; will that interval usually be on the order of three hours, no matter the distance away from us?

[lpetrich]

David B, I think that you are mixing up a gamma-ray-burst supernova and a regular Type II supernova. A GRB supernova would most likely be a Type Ic one.

A GRB supernova will most likely emit its flash of gamma rays when it emits its flash of neutrinos, because of the high temperatures necessary.

So a regular Type II supernova would not emit a GRB because of its thick outer layers. However, its neutrinos can still get through those layers.

What happened 3 hours after SN 1987a's neutrino flash was its shock front reaching the surface and brightening it. Red supergiants like Antares, Betelgeuse, and VY CMa are much larger than SN 1987a's progenitor, meaning that the shock will take longer to reach the surface for them.

I've found some class notes (http://www.astro.princeton.edu/~burrows/classes/541/shock_breakout.pdf) that include some calculations of shock breakout times.

For a blue supergiant, it's about 2 hours, while for a red supergiant, it's about 20 hours.

Now for some sizes:

Red Supergiant: 500 - 1000 RSun
Blue Supergiant: 25 - 50 RSun
Wolf-Rayet: 5 - 10 RSun

[Jobar]

So the delay between neutrino burst and photon flash is closely related to the stellar radius- more exactly, related to the distance between the forming neutron star in the core and the visible surface of the star, and the density of the outer layers. I'm a bit surprised that it takes so long for a red supergiant, but not greatly so.

There's an answer for James Bannon. Since we know VY CMa is a very large red supergiant, we can expect that we'll detect the neutrino burst from it around 20 hours before the photons arrive. That would be enough time to do a lot of things to guard our electronics, if the radiation front was going to be intense enough to do us any real damage.

[JamesBannon]

If I'm reading the "sciency" stuff correctly, Vy CMa is unlikely to form a GRB anyway, since it's not massive enough. However, a Wolf-Rayet star might well be massive enough to give off a GRB when it collapses under its own weight. And, since it has lost much of its outer atmospheric layers, the delay between the "front guard" and "main strike" will be much shorter, since the photons don't have to migrate through a large gas cloud.

[Jobar]

Well, it IS massive enough- 20 to 25 solar masses. But because it still has so much of its outer layers, the gamma rays will be converted to longer wavelengths coming through them.

[Jobar]

Here's a good YouTube explanation of neutron star "fromation", which is what powers a supernova. Some of the related videos are also well worth watching.
http://www.youtube.com/watch?v=jT2wkbPfUYc

A more basic explanation of supernovas-
http://www.youtube.com/watch?v=bSS7xgr5P8c&feature=related

[David B]

David B, I think that you are mixing up a gamma-ray-burst supernova and a regular Type II supernova. A GRB supernova would most likely be a Type Ic one.


:o Yes, I think I was:(

I'll check out Jobar's links when I've caught up with the board.

David

[Eudaimonist]

A nearby nova seems like a good time to detect "gravity waves". When would those arrive, assuming they exist?


eudaimonia,

Mark

[lpetrich]

The shock-breakout times of 2 hours for blue supergiants and 20 hours for red ones are likely for "average" ones; I'd have to find what assumed sizes were used in these calculations to be sure. This would make the breakout time for VY CMa something like 2 or 3 days (it's that big).

Resolved picture of Betelgeuse: HubbleSite - NewsCenter - Hubble Space Telescope Captures First Direct Image of a Star (12/10/1996) - Release Images (http://hubblesite.org/newscenter/archive/releases/1996/04/image/a/)

I've also found Shedding Light on Betelgeuse and VY Canis Majoris as Future Supernovae | Gemini Observatory (http://www.gemini.edu/node/11206)

I can't find much on Antares, however.

Gravitational radiation? It travels at c, the speed of light in a vacuum, so it would arrive when the neutrino flash arrived.

Those neutrinos would likely be detected by participants in the SNEWS (Supernova Early Warning System) (http://snews.bnl.gov/) network. They are set up to alert when they see a big flash of neutrinos, and if several places see such neutrino events, then they send the word out to look for visible evidence of a supernova.

[Eudaimonist]

Betelgeuse? What a tiny star!

...compared to VY Canis Majoris (http://en.wikipedia.org/wiki/VY_Canis_Majoris)...


eudaimonia,

Mark

[lpetrich]

:D

More pictures of Betelgeuse:

Surface imaging of Betelgeuse (http://www.mrao.cam.ac.uk/telescopes/coast/betel.html)
Mang's Bat Page: Betelgeuse, Betelgeuse, Betelgeuse! (http://mangsbatpage.433rd.com/2009/01/betelgeuse-betelgeuse-betelgeuse.html)
Sharpest views of Betelgeuse reveal how supergiant stars lose mass Unveiling the true face of a behemoth | SpaceRef - Your Space Reference (http://www.spaceref.com/news/viewpr.html?pid=28852)

[Loren Pechtel]

They were emitted about 3 hours before that supernova was observed in the visible.

Let's call those neutrinos the "advanced guard". Detecting them means we have approximately 3 hours before the "main force" strikes. That's not an awful lot of time. By the time anyone gets to hear of it, the main force will have arrived and scorched us, assuming that is what will happen.

If this was taken seriously and prepared for, it would give an hour to verify that we were in deep shite, another hour to broadcast on every channel, and get the cops going through the streets with loudspeakers, that people should switch everything off, and pull all the plugs. And another hour for the people running the power system to switch off and get as much as possible isolated from everything else.

Even if it means blowing down power lines. Isolating things is good.

At least, that is the impression I got looking at some documentrary about what the sun could potentially do at the worst of its cycle.

David

But how would you know if the gamma ray burst was heading for us or not? The odds of it scoring a hit are quite low.

Anyway, you don't need to blow them down. Open every circuit breaker everywhere and short across anything connected to a long wire. The surge will take the short rather than the opened breaker.

[Jobar]

http://www.gemini.edu/images/stories/websplash/ws2008-25/fig3.gif

That looks weird.

What causes those asymmetrical lobes? It seems I recall reading an article in Scientific American some years back, about core conditions inside stars which have gone off the main sequence and are beginning to fuse elements above hydrogen. There may be localized 'clumps' of material which reach temperatures hot enough to start off higher-order fusion processes, if I'm recalling correctly; this would result in vast explosions which might blow pieces of the outer layers free of the star's gravitational well. That figure makes such asymmetrical explosions look very plausible.

[lpetrich]

What causes those asymmetrical lobes?
Large-scale turbulence on its surface, I think. Like what happens on the Sun: coronal mass ejections.

I found a Wikipedia article on the solar storm of 1859:
On September 1–2, 1859 the largest recorded geomagnetic storm occurred, causing the failure of telegraph systems all over Europe and North America. Auroras were seen around the world, most notably over the Caribbean; also noteworthy were those over the Rocky Mountains that were so bright, the glow awoke gold miners, who began preparing breakfast because they thought it was morning.

[Eudaimonist]

Just so long as the Earth's magnetic field still protects us from the worst radiation, I think we'll be fine. Just don't be on a Mars mission at that time.


eudaimonia,

Mark
But, gamma rays aren't particles.

Except insofar as a photon is a particle. However, uncharged.

I thought that there was some protection offered by a magnetic field from cosmic radiation. Here is what I was talking about.

http://science.nasa.gov/headlines/y2009/23dec_voyager.htm

The fact that the Fluff is strongly magnetized means that other clouds in the galactic neighborhood could be, too. Eventually, the solar system will run into some of them, and their strong magnetic fields could compress the heliosphere even more than it is compressed now. Additional compression could allow more cosmic rays to reach the inner solar system, possibly affecting terrestrial climate and the ability of astronauts to travel safely through space.


eudaimonia,

Mark

[Schneibster]

CJO - Abstract - Did a gamma-ray burst initiate the late Ordovician mass extinction? (http://journals.cambridge.org/action/displayAbstract;jsessionid=1C5F2761949DF806C1F90DC BF6D1A6BC.tomcat1?fromPage=online&aid=240775)

Gamma-ray bursts (GRBs) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average two or more times per billion years. At least five times in the history of life, the Earth has experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRBs may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. A special feature of GRBs in terms of terrestrial effects is a nearly impulsive energy input of the order of 10 s. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.

This is the Ordovician–Silurian extinction event

The main problem with the GRB hypothesis is the failure to find any traces in the rocks of anything that can plausibly be interpreted as being specifically caused by a GRB. Nothing like the K-T iridium layer, which implies that something or other had spewed or blasted a lot of iridium-containing dust into the air at the exact time of that extinction. However, we may not know what to look for, and someone may find some geochemical clue for recognizing (say) increased solar UV.I've seen a fair bit of the evidence for this and I don't think so. The evidence is quite good for an ice age due to Gondwana covering the South Pole; and there is excellent evidence that a continent over a pole causes an ice age due to shutting down the thermohaline cycle.

While a GRB remains a possibility, it's probability is much lower.

[lpetrich]

What a GRB could have done here was to induce the starting of that ice age. This would happen by creating a nitrogen-oxide haze, which would block some sunlight and which would cause a cold snap for a few years. The resulting very cold winters and cool summers would cause snow to fall over larger areas and melt much slower, causing that ice age.

[Schneibster]

Right, but putting a continent over a pole seems to cause an ice age every time it happens. I'm pretty skeptical of a GRB coming along conveniently every time that happens.