May 7, 2007 8:56 PM   Subscribe

posted by spock at 9:16 PM on May 7, 2007 [2 favorites]

There was a theory that stars massing over 100 solar masses would "hypernova" -- the core collapse would be so rapid and massive that the core would become a black hole almost instantly, leaving a much larger void in the center of the star than a normal type II supernova would, and the resulting crush of infalling matter would result in a very bright, very long lived explosion.

They were initially posited as a candidate for gamma ray bursts, but have since fallen out of favor. This may need to be revisited -- this looks very similar to the initial hypernova descriptions.

Or maybe it's something else. Science is like that.
posted by eriko at 9:19 PM on May 7, 2007

You know, I knew it was a mistake to compile all the names of God.
posted by Astro Zombie at 9:25 PM on May 7, 2007 [4 favorites]

No kidding. That's clearly a job for Lisp or Perl, not some silly compiled language.
posted by eriko at 9:30 PM on May 7, 2007 [1 favorite]

(Sounds like a crazy scheme to me)
posted by b1tr0t at 9:54 PM on May 7, 2007

Oops, my bad. I knew I shouldn't have crossed the streams.
posted by Foosnark at 11:24 PM on May 7, 2007

yes, it's true. burned too brightly for its own good :)
posted by mrballistic at 11:28 PM on May 7, 2007 [1 favorite]

If you don't compile the names of God, though, you'll be crippled by interpreter errors.
posted by fleacircus at 11:28 PM on May 7, 2007 [1 favorite]

The original article is here. It's surprisingly readable.
posted by ikkyu2 at 11:29 PM on May 7, 2007

Actually, hypernovae are still the most popular theory for long-duration gamma ray bursts (as opposed to short-duration bursts, which are not nearly as well understood, but are thought to be neutron star or neutron star-black hole collisions), though it's by no means settled. The idea is that you have a massive (40 solar masses or more), rapidly rotating progenitor that explodes and forms jets, which we see as the gamma ray burst.

As for the supernova mentioned in the article, the working hypothesis is that it's a pair-instability supernova. Basically, these stars are so massive (between 150 and 260 solar masses) that the core gets hot enough for photons to collide and form electron-positron pairs (which quickly collide and turn back into photons), which causes the star to become unstable and (wave hands) causes an explosion energetic enough to rip the star apart before it can collapse to a black hole.

Pair-instability supernovae are thought to be common in the first stars in the universe, when matter was pretty much just hydrogen and helium. The reason is because stars much above 100 solar masses are very hard to produce in the modern, "polluted" universe. The more massive the star, the more light it produces, and elements like carbon and iron are very good at "catching" light and blowing the star apart before it has a chance to form. For similar reasons it's hard to keep a star very massive throughout it's life. The metals in the outer layers catch the star's light and the star peels off it's outer layers as it ages. But in the very early universe, there weren't any metals (well, very little), so stars could get big and stay big, thus becoming pair unstable. This discovery has big implications for both massive star evolution and for the study of the early universe.
posted by dirigibleman at 11:53 PM on May 7, 2007 [4 favorites]

Wait, so sayin' that this supernova is fueled by antimatter? Is that what I'm reading, dirigibleman? Because, that's super cool to this man who's astronomy studies ended in High School.
posted by Mister Cheese at 12:15 AM on May 8, 2007

Urk, that should read, "so you're saying". I'm not to clear on what pair instable means. Photons have mass? They can collide to form electrons and positrons?

On one level it's so abstract that it defies true understanding for me, but on the other hand it just feels so much cooler/grander than human biology. I always wished that I'd the guts to major in astronomy.

I guess I shall just have to be content with reading stuff on the internets.
posted by Mister Cheese at 12:22 AM on May 8, 2007

If a photon's got more than about a megaelectronvolt of energy then it can, in the right circumstances, convert into an electron and a positron. By the right circumstances I mean it needs something to dump momentum on, as a photon on its own can't just turn into a positron and electron on its own whilst conserving both energy and momentum. This'd normally be an atomic nucleus or something, which obviously are quite common inside stars, so this can happen quite easily.

It's not the resulting positron and electron annihilating that's the 'fuel' for the supernova though. After all, that energy just came from the photon you used to make the pair. The problem is that until this process starts those photons were the major component of the pressure supporting the star, and if you start having a certain proportion* disappear and get replaced with electron-positron pairs you've lost a significant chunk of the pressure, and the star collapses inwards.

It's that (rather sudden) inwards collapse that sets off more nuclear reactions in the core and makes the whole thing go kablooie (to use the technical term).

*the pairs will start forming and annihilating all the time, so you'll get new photons back, but the forwards-and-backwards process will still result in a troublesome loss of the pressure from the radiation.
posted by edd at 3:53 AM on May 8, 2007

Oops, change that. It seems the pair annihilations don't give you back photons but tend to pop out neutrinos instead, so you really would have quite a dramatic loss of pressure.
posted by edd at 3:55 AM on May 8, 2007

One word: Galactus.
posted by the sobsister at 5:00 AM on May 8, 2007

It seems the pair annihilations don't give you back photons but tend to pop out neutrinos instead

Yes -- you release 100 Foe worth of energy as Neutrinos -- much more in a hypernova. One of the big gaps in the supernova model is "How does the neutrino flux blow the star apart?"

If we hand wave the first second after the collapse, and accept that 1% of the neutrino flux is captured by the infalling mass, we get a model that matches the observed data quite well. Problem: Neutrino -> mass interaction rates, as we understand them, don't support transferring that much energy to the infalling mass.

IOW, under our current understanding of neutrinos, instead of 99 Foe escaping, we should see 99.9 Foe escaping, and the start doesn't blow up.

you really would have quite a dramatic loss of pressure.

Yes. Between the iron core of the star becoming degenerate matter (or, in a hypernova, a black hole) and the neutrino flux, a whole lot of matter that was at the core goes elsewhere very quickly.
posted by eriko at 5:14 AM on May 8, 2007

Why is this on the front page? This happened 240 million years ago.
posted by Pastabagel at 7:00 AM on May 8, 2007 [9 favorites]

I guess my critical-reading skills aren't what they once were, because when I read "too bright" I started thinking "too bright for what or whom?" and didn't feel like the linked article answered that question. What I got was that the phenomenon of hypernovae was poorly understood but really interesting.
posted by pax digita at 8:32 AM on May 8, 2007

eriko: these stars don't get to the point where they have an iron core: the core collapse caused by the loss of light pressure triggers a conflagration where all the oxygen and silicon (IIRC) in the core burns (by nuclear fusion) pretty much at once to heavier elements, and the amount of energy absorbed is greater than the gravitational binding energy of the star.

A similar kind of conflagration is what happens to type Ia supernovae, but on a much smaller scale — the outcome is the same however in that there's nothing left of the core of the star afterwards, it's all been blown apart into the interstellar medium.

This article has some more details.

(it feels a little odd to be able to describe a type 1a supernovae as being 'on a much smaller scale' — these hypernovae are incredibly powerful.)
posted by pharm at 9:53 AM on May 8, 2007

I was just doing some research into Eta Carinae a couple of weeks ago. It's really hard to get your mind around the idea of something that... big.

This is a link I saw on Mefi not that long ago. Notice how friggin' big Antares is? Eta Carinae is almost ten times bigger.

It's really really really unimaginably big.


posted by quin at 11:17 AM on May 8, 2007 [1 favorite]

I blame Guitar Hero.
Someone is just rocking SO hard they’re influencing celestial events.
Those young stars lived fast and exploded violently.
Don’t you kids go doing that. Stay in school. Don’t do drugs.

Interesting stuff btw. pharm - I wasn’t aware mass loss could be driven by nuclear pulsations, or that there were nonrotating pulsational instabilities. Makes sense though, you think “pulsar” and it rotates etc. So what if it doesn’t, but it’s got a lot of extra energy. Yeah.
posted by Smedleyman at 11:29 AM on May 8, 2007

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