Questions regarding supernovae

[Graham Kennedy]

I am working on a science fiction story and I'd like a little clarification if possible.

In the story, a star is going to go supernova and the result will be a rapidly spinning pulsar. The issues I have are these :

First, how predictable are supernovas? What I want is for the characters not to realise that this particular star is going to blow until shortly before it does, so it comes as a surprise to them. Is that a feasible thing? I know you can say that a star might go bang sometime soon, but with soon meaning millions of years, but if you were up close to a star that was going to go supernova next month it would be really obvious? And what kind of sun are we talking here? A Red Giant?

Second, what would happen to a planetary system when the star did go supernova? Are all the planets vapourised, or is it possible that they would still be there afterwards? Might people on a planet even survive, if they had enough protection from radiation and such?

Third, from what I've read of supernovae, my mental image is of the star collapsing, then becoming massively bright - billions of times normal - whilst clouds of gas are being blasted up and away from it. And at the end of a few weeks you have a new pulsar. Is that about right? Would there be any other obvious stuff going on at the same time?

[korjik]

You might have a few hour/days notice. IIRC, the final stage of a type II supernova is silicon burining into iron, and the rate of burning the silicon is high enough that all is burned in a day or so. You might be able to tell what is burning in the core by using a couple neutrino telescopes.

I dont remember how long the silicon burning takes, or wether the core will collapse quickly after it done, or if the neutrino spectrum would be sufficiently different to beable to tell what is burning.

The planets are toast. Even if they dont get vaporized, the SN is probably bright enough to melt the surface. Then after the blast front of the SN passes, the orbits will get expanded to take into account the lower mass of the neutron star.

The only way people could survive is to be able to take the heat, and also have something that blocks the neutrinos. If you cant block the neutrinos, everyone will at the very least die of radiation poisoning, at the worst, get baked from the inside out.

I dont think that visually you would have any indication that the supernova is occuring. It happens quickly enough that the outer layers dont really know the collapse has occured until after the blast front passes.

[Graham Kennedy]

So if I read you right, even in the last stages it's pretty much a normal star, visually, and then suddenly the outer layers are being blasted off in a huge explosion, with no warning? But with neutrino detectors and such you might tell what is going on in the core over the last few days.

As for planets... blasted clean of life, surface melted, but still physically there?

I never thought about the orbits shifting to further from the sun, obvious really. How much mass is lost, typically? Would the orbits change a lot?

The only way people could survive is to be able to take the heat, and also have something that blocks the neutrinos. If you cant block the neutrinos, everyone will at the very least die of radiation poisoning, at the worst, get baked from the inside out.

I'm sorry, you'll get radiation damage from neutrinos? Did you mean to say neutrons here?

Thanks for your help, it's very informative so far!

[grant hutchison]

I'm sorry, you'll get radiation damage from neutrinos? Did you mean to say neutrons here?

Neutrinos. Supernovae produce a lot of neutrinos, and they escape before the explosion takes place. Depending on the energy spectrum, even the minuscule proportion of neutrinos that are stopped by human bodies could deliver enough energy to cause damage.

Grant Hutchison

[trinitree88]

As the star goes through it's sequence of isotopes fusing , the leakiness of neutrinos increases each time, requiring faster and faster fuel burning. A neutrino detector on a nearby planet ought to see that.
There might be an acoustical signal in the solar oscillations, too. Increased density of the core, and higher temperatures, ought to change the spherical harmonics, too, though one may compensate for the other.
The time for the iron core to accumulate varies a great deal from weeks to months in different models...even years, in some.
There should be a distinct change in the stars spectral signature as heavier elements accumulate in the mix. Old models said it doesn't mix but recent spectra of Alnitak say that's not quite kosher.....and led to my bet with Antoniseb, that it'd go in a few years...(Shhh! it's still there...and I paid up already...)pete

[Cougar]

First, how predictable are supernovas? What I want is for the characters not to realise that this particular star is going to blow until shortly before it does, so it comes as a surprise to them. Is that a feasible thing?

Well, in science fiction, you can give the population any level of intelligence that you want. An advanced civilization would be able to predict pretty accurately when it would occur by measuring the (changing) ratios of the elements and the shell temperatures. You'll want to study up on stellar evolution...

...if you were up close to a star that was going to go supernova next month it would be really obvious? And what kind of sun are we talking here? A Red Giant?

I believe if your star¹ was going to go supernova next month, your planet would already be sterilized by the huge stellar winds (if not consumed by the star's expansion). Stars massive enough to go supernova go through some fairly drastic changes long before the explosion....

Second, what would happen to a planetary system when the star did go supernova? Are all the planets vapourised, or is it possible that they would still be there afterwards? Might people on a planet even survive, if they had enough protection from radiation and such?

No, the only sensible thing to do would be to leave the system.

________________________
¹ Probably a Red Supergiant

[astromark]

And according to me we are watching some stars for just such changes... and have found. Betelgeuse and Omega Cent.,to be prime candidates. Also of interest is Antares and one of the obvious stars of the Jewel Box ( crux ) is very red.
Fortunately all of these are considered as safe from our point of view.

[DarkHorse220]

Second, what would happen to a planetary system when the star did go supernova? Are all the planets vapourised, or is it possible that they would still be there afterwards? Might people on a planet even survive, if they had enough protection from radiation and such?

Even the Xeelee pack up and high-tail it out of there when a supernova comes calling. Anybody less than that would not have a good day.

[Graham Kennedy]

Okay, it seems that my original plot isn't going to be scientifically plausible so I'll have to rework it (how often do you hear that! )

For a bit of context, the original idea was that they were going to study a star that was close to supernova, with close meaning "could be as little as a million years!" When they got there they would have found that it was actually very, very close indeed - and as it turned out it would go bang a couple of weeks later. In terms of survival I had hoped to have a few characters get stranded on one of the planets when their ship was occupied and have to ride out the supernova there, perhaps by letting them shelter in deep caves or at the bottom of an ocean or something.

So now I'm thinking that you would have months or even years of notice, which means the whole "wow, it's about to blow" aspect would actually have to happen as they approached the star and got to within a few light years and then light months of it.

I'd still like to strand some people... have to think about that one. Perhaps if they were on the far side of a large tidally locked planet. Though they would need protection from the neutrinos still - and by the way, thanks for that, the idea of having so many neutrinos that they can actually affect a person just tickles me after so long of thinking them as being the next best thing to totally insubstantial!

I may have more questions, but for now that's hugely for all the contributions! I have to rework half my story!

[chornedsnorkack]

________________________
¹ Probably a Red Supergiant

Quite generally, stars massive enough to be a supernova of first kind are too massive, and too shortlived on the main sequence, to be a good primary for a longlived planet.

However, you could have a rather unpleasantly close supernova in the neighbourhood...

It does not have to be a red supergiant. Sanduleak 69202 was an unremarkable blue supergiant on main sequence.

And then you have supernovas of first kind. Whose progenitors are rather long-lived white dwarfs.

You might have a triple star whose one component explodes as a supernova...

[Cougar]

Quite generally, stars massive enough to be a supernova of first kind are too massive, and too shortlived on the main sequence, to be a good primary for a longlived planet.

Ooh, right.

However, you could have a rather unpleasantly close supernova in the neighbourhood...

There you go.

It does not have to be a red supergiant. Sanduleak 69202 was an unremarkable blue supergiant on main sequence.... And then you have supernovas of first kind. Whose progenitors are rather long-lived white dwarfs.

Quite right - there are several different kinds of supernovas. In all cases, you'll have to be at a fair distance for the possibility of survival.

...the original idea was that they were going to study a star that was close to supernova...

If they're advanced enough for interstellar travel, they should have a very good estimate for when the star is going to go off.

[timb]

Quite generally, stars massive enough to be a supernova of first kind are too massive, and too shortlived on the main sequence, to be a good primary for a longlived planet.

Supernovae of the "first kind" versus

And then you have supernovas of first kind. Whose progenitors are rather long-lived white dwarfs.

supernovae of the "first kind"?

It does not have to be a red supergiant. Sanduleak 69202 was an unremarkable blue supergiant on main sequence.

There are no supergiants on the main sequence.

[chornedsnorkack]

Supernovae of the "first kind" versus



supernovae of the "first kind"?

Sorry. The massive stars are supernovae of second kind.

[slang]

I believe if your star¹ was going to go supernova next month, your planet would already be sterilized by the huge stellar winds (if not consumed by the star's expansion). Stars massive enough to go supernova go through some fairly drastic changes long before the explosion....

Graham did not stipulate that the unpleasantly suprised characters in his story were on their homeplanet, or did he? So it could be some sufficienty radiation protected interstellar expedition (maybe even interplanetary, if they're alien enough) that just happened to be a little to close for the main event. The fact that the star was doing some weird stuff might even have been the reason for the expedition. Did I save your story, Graham?

[Kwalish Kid]

There is a possible scenario that might fit the needs of the narrative.

Say, from a distance, the crew sees a white dwarf star orbiting a young star. Given the rate at which the young star is losing gas to the dwarf, they could predict when the dwarf star would reach the Chandrasekhar limit and then go supernova. When the crew got there, they could find out that the dwarf star drifted into the solar system, where it began to orbit the young star, so there are planets in the system of the young star. Then, later, the crew could discover that the solar system was originally a binary system and that the other star in the system will be coming close enough to the dwarf star to tip it over the edge very soon.

Now, the real questions are, "Will the supernova leave anything of the planets?" and, "Can the crew survive in the planet the two months it will take for the supernovae to build to peak output and then trail off?"

[StupendousMan]

There is a possible scenario that might fit the needs of the narrative.

Say, from a distance, the crew sees a white dwarf star orbiting a young star. Given the rate at which the young star is losing gas to the dwarf, they could predict when the dwarf star would reach the Chandrasekhar limit and then go supernova. When the crew got there, they could find out that the dwarf star drifted into the solar system, where it began to orbit the young star, so there are planets in the system of the young star.

The chance that a white dwarf will be captured by an isolated star as it passes through the system is very, very small -- and if such a capture _did_ happen, it would very probably leave the white dwarf in an elliptical orbit which would not accrete matter in a predictable manner.

Your post goes on to posit the existence of a THIRD star in this system, one which was part of an original binary before the white dwarf came along. That third star would increase the chances that the white dwarf might be captured, but, in that case, I think it's very likely that the third star would be ejected from the system as a result.

Sigh. This is a tough scenario to create :-/

[chornedsnorkack]

A simple scenario for a supernova of first kind to be associated with planets is a hierarchical triple. Like Keid or Algol.

Two unequally massive stars orbiting close to each other - the third (less massive than either of the two) further away, with its planets.

When A finishes main sequence, it becomes a red giant, then white dwarf - C is far enough that the planets are not seriously harmed by the red giant. Then B becomes red giant - and white dwarf A picks up mass. Leading to nova and finally supernova explosion.

BTW, there are several recurrent novae. Are there any stars which have been both a nova and a supernova?

But getting a supernova of second kind, which leaves a pulsar, to be associated with an old star and planets is harder... supernovae of second kind are young.

How do diffuse nebulae interact with old, low-mass stars? If an old star enters into, or gets in the way of, a cold and massive gas cloud, could a massive star form because of the gravity of the old star?

[timb]

A simple scenario for a supernova of first kind to be associated with planets is a hierarchical triple. Like Keid or Algol.

Two unequally massive stars orbiting close to each other - the third (less massive than either of the two) further away, with its planets.

When A finishes main sequence, it becomes a red giant, then white dwarf - C is far enough that the planets are not seriously harmed by the red giant. Then B becomes red giant - and white dwarf A picks up mass. Leading to nova and finally supernova explosion.

BTW, there are several recurrent novae. Are there any stars which have been both a nova and a supernova?

But getting a supernova of second kind, which leaves a pulsar, to be associated with an old star and planets is harder... supernovae of second kind are young.

How do diffuse nebulae interact with old, low-mass stars? If an old star enters into, or gets in the way of, a cold and massive gas cloud, could a massive star form because of the gravity of the old star?

That would just be a nearby star going supernova. That can happen anyway. A Type II going off a few light years away would be damaging, though I don't think planets would be vaporized.

Stellar fusion could cause an unusually long delay between star formation and supernova. If, say, a pair of twin B stars in a very close binary merged due to orbital decay, the resultant star might be massive enough to supernova. Of course anyone orbiting would experience a large increase in irradiance due to the merger, and B stars don't last very long anyway.

[chornedsnorkack]

That would just be a nearby star going supernova. That can happen anyway. A Type II going off a few light years away would be damaging, though I don't think planets would be vaporized.

If an old star enters into a dense, star-forming gas cloud/protostar cluster, could the old star (and its planets) be captured into a binary star with a massive star as it forms - or indeed cause a star to form in its vicinity? Well closer than a few lightyears, that is?

[trinitree88]

The latest type 1-a models indicate that a companion needs to be at the helium burning stage for the white dwarf to explode properly.

[timb]

The latest type 1-a models indicate that a companion needs to be at the helium burning stage for the white dwarf to explode properly.

That sounds unlikely to me. The CO white dwarf explodes when its mass reaches the vicinity of the Chandrasekhar limit. That could happen without it even having a companion.

[korjik]

That sounds unlikely to me. The CO white dwarf explodes when its mass reaches the vicinity of the Chandrasekhar limit. That could happen without it even having a companion.

Why does it sound unlikely?

By far the easiest way to get to carbon burning in a CO wd would be to have mass transfer from a binary companion. Easiest way to get a mass transfer is to have a companion fill its Roche lobe. Easiest way to have the Roche lobe fill after the creation of the wd is to have the companion start helium burning after the wd is created.

To have a type Ia otherwise would require the wd to be pretty big in the first place. With a mass transfer, you may be able to have a comparatively small wd get bulked up enough to boom

[Hornblower]

That sounds unlikely to me. The CO white dwarf explodes when its mass reaches the vicinity of the Chandrasekhar limit. That could happen without it even having a companion.

Without a companion, there would be no source of material to bulk it up and over the limit.

[timb]

Why does it sound unlikely?

By far the easiest way to get to carbon burning in a CO wd would be to have mass transfer from a binary companion. Easiest way to get a mass transfer is to have a companion fill its Roche lobe. Easiest way to have the Roche lobe fill after the creation of the wd is to have the companion start helium burning after the wd is created.

You should learn the difference between necessity and possibility.

Without a companion, there would be no source of material to bulk it up and over the limit.

Stars can collide with objects that are not companions.

[Hornblower]

You should learn the difference between necessity and possibility.



Stars can collide with objects that are not companions.

That is true, but the odds against a collision are collossal, while binaries are commonplace.

[korjik]

You should learn the difference between necessity and possibility.



Stars can collide with objects that are not companions.

I'm the one who should learn the difference?!?

My example is one of the more common situations in the universe and your is something that may happen twice when Andromeda collides with the Milky Way.

My example can get almost any wd to SNIa, yours requires a wd right on the cusp to have a collision with a massive object.

One of us needs to learn the difference, and it is not me