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The Star That Exploded At the Dawn of Time

samzenpus posted about 2 months ago | from the in-the-beginning dept.

Space 55

sciencehabit writes To probe the dawn of time, astronomers usually peer far away; but now they've made a notable discovery close to home. An ancient star a mere thousand light-years from Earth bears chemical elements that may have been forged by the death of a star that was both extremely massive and one of the first to arise after the big bang. If confirmed, the finding means that some of the universe's first stars were so massive they died in exceptionally violent explosions that altered the growth of early galaxies.

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Your official guide to the Jigaboo presidency. (-1, Flamebait)

Anonymous Coward | about 2 months ago | (#47726345)

Congratulations on your purchase of a brand new nigger! If handled properly, your apeman will give years of valuable, if reluctant, service.

INSTALLING YOUR NIGGER.

You should install your nigger differently according to whether you have purchased the field or house model. Field niggers work best in a serial configuration, i.e. chained together. Chain your nigger to another nigger immediately after unpacking it, and don't even think about taking that chain off, ever. Many niggers start singing as soon as you put a chain on them. This habit can usually be thrashed out of them if nipped in the bud. House niggers work best as standalone units, but should be hobbled or hamstrung to prevent attempts at escape. At this stage, your nigger can also be given a name. Most owners use the same names over and over, since niggers become confused by too much data. Rufus, Rastus, Remus, Toby, Carslisle, Carlton, Hey-You!-Yes-you!, Yeller, Blackstar, and Sambo are all effective names for your new buck nigger. If your nigger is a ho, it should be called Latrelle, L'Tanya, or Jemima. Some owners call their nigger hoes Latrine for a joke. Pearl, Blossom, and Ivory are also righteous names for nigger hoes. These names go straight over your nigger's head, by the way.

CONFIGURING YOUR NIGGER

Owing to a design error, your nigger comes equipped with a tongue and vocal chords. Most niggers can master only a few basic human phrases with this apparatus - "muh dick" being the most popular. However, others make barking, yelping, yapping noises and appear to be in some pain, so you should probably call a vet and have him remove your nigger's tongue. Once de-tongued your nigger will be a lot happier - at least, you won't hear it complaining anywhere near as much. Niggers have nothing interesting to say, anyway. Many owners also castrate their niggers for health reasons (yours, mine, and that of women, not the nigger's). This is strongly recommended, and frankly, it's a mystery why this is not done on the boat.

HOUSING YOUR NIGGER.

Your nigger can be accommodated in cages with stout iron bars. Make sure, however, that the bars are wide enough to push pieces of nigger food through. The rule of thumb is, four niggers per square yard of cage. So a fifteen foot by thirty foot nigger cage can accommodate two hundred niggers. You can site a nigger cage anywhere, even on soft ground. Don't worry about your nigger fashioning makeshift shovels out of odd pieces of wood and digging an escape tunnel under the bars of the cage. Niggers never invented the shovel before and they're not about to now. In any case, your nigger is certainly too lazy to attempt escape. As long as the free food holds out, your nigger is living better than it did in Africa, so it will stay put. Buck niggers and hoe niggers can be safely accommodated in the same cage, as bucks never attempt sex with black hoes.

FEEDING YOUR NIGGER.

Your Nigger likes fried chicken, corn bread, and watermelon. You should therefore give it none of these things because its lazy ass almost certainly doesn't deserve it. Instead, feed it on porridge with salt, and creek water. Your nigger will supplement its diet with whatever it finds in the fields, other niggers, etc. Experienced nigger owners sometimes push watermelon slices through the bars of the nigger cage at the end of the day as a treat, but only if all niggers have worked well and nothing has been stolen that day. Mike of the Old Ranch Plantation reports that this last one is a killer, since all niggers steal something almost every single day of their lives. He reports he doesn't have to spend much on free watermelon for his niggers as a result. You should never allow your nigger meal breaks while at work, since if it stops work for more than ten minutes it will need to be retrained. You would be surprised how long it takes to teach a nigger to pick cotton. You really would. Coffee beans? Don't ask. You have no idea.

MAKING YOUR NIGGER WORK.

Niggers are very, very averse to work of any kind. The nigger's most prominent anatomical feature, after all, its oversized buttocks, which have evolved to make it more comfortable for your nigger to sit around all day doing nothing for its entire life. Niggers are often good runners, too, to enable them to sprint quickly in the opposite direction if they see work heading their way. The solution to this is to *dupe* your nigger into working. After installation, encourage it towards the cotton field with blows of a wooden club, fence post, baseball bat, etc., and then tell it that all that cotton belongs to a white man, who won't be back until tomorrow. Your nigger will then frantically compete with the other field niggers to steal as much of that cotton as it can before the white man returns. At the end of the day, return your nigger to its cage and laugh at its stupidity, then repeat the same trick every day indefinitely. Your nigger comes equipped with the standard nigger IQ of 75 and a memory to match, so it will forget this trick overnight. Niggers can start work at around 5am. You should then return to bed and come back at around 10am. Your niggers can then work through until around 10pm or whenever the light fades.

ENTERTAINING YOUR NIGGER.

Your nigger enjoys play, like most animals, so you should play with it regularly. A happy smiling nigger works best. Games niggers enjoy include: 1) A good thrashing: every few days, take your nigger's pants down, hang it up by its heels, and have some of your other niggers thrash it with a club or whip. Your nigger will signal its intense enjoyment by shrieking and sobbing. 2) Lynch the nigger: niggers are cheap and there are millions more where yours came from. So every now and then, push the boat out a bit and lynch a nigger.

Lynchings are best done with a rope over the branch of a tree, and niggers just love to be lynched. It makes them feel special. Make your other niggers watch. They'll be so grateful, they'll work harder for a day or two (and then you can lynch another one). 3) Nigger dragging: Tie your nigger by one wrist to the tow bar on the back of suitable vehicle, then drive away at approximately 50mph. Your nigger's shrieks of enjoyment will be heard for miles. It will shriek until it falls apart. To prolong the fun for the nigger, do *NOT* drag him by his feet, as his head comes off too soon. This is painless for the nigger, but spoils the fun. Always wear a seatbelt and never exceed the speed limit. 4) Playing on the PNL: a variation on (2), except you can lynch your nigger out in the fields, thus saving work time. Niggers enjoy this game best if the PNL is operated by a man in a tall white hood. 5) Hunt the nigger: a variation of Hunt the Slipper, but played outdoors, with Dobermans. WARNING: do not let your Dobermans bite a nigger, as they are highly toxic.

DISPOSAL OF DEAD NIGGERS.

Niggers die on average at around 40, which some might say is 40 years too late, but there you go. Most people prefer their niggers dead, in fact. When yours dies, report the license number of the car that did the drive-by shooting of your nigger. The police will collect the nigger and dispose of it for you.

COMMON PROBLEMS WITH NIGGERS MY NIGGER IS VERY AGGRESIVE

Have it put down, for god's sake. Who needs an uppity nigger? What are we, short of niggers or something?

MY NIGGER KEEPS RAPING WHITE WOMEN

They all do this. Shorten your nigger's chain so it can't reach any white women, and arm heavily any white women who might go near it.

WILL MY NIGGER ATTACK ME?

Not unless it outnumbers you 20 to 1, and even then, it's not likely. If niggers successfully overthrew their owners, they'd have to sort out their own food. This is probably why nigger uprisings were nonexistent (until some fool gave them rights).

MY NIGGER BITCHES ABOUT ITS "RIGHTS" AND "RACISM".

Yeah, well, it would. Tell it to shut the fuck up.

MY NIGGER'S HIDE IS A FUNNY COLOR. WHAT IS THE CORRECT SHADE FOR A NIGGER?
A nigger's skin is actually more or less transparent. That brown color you can see is the shit your nigger is full of. This is why some models of nigger are sold as "The Shitskin".

MY NIGGER ACTS LIKE A NIGGER, BUT IS WHITE.

What you have there is a "wigger". Rough crowd.

IS THAT LIKE AN ALBINO? ARE THEY RARE?

They're as common as dog shit and about as valuable. In fact, one of them was President between 1992 and 2000. Put your wigger in a cage with a few hundred genuine niggers and you'll soon find it stops acting like a nigger. However, leave it in the cage and let the niggers dispose of it. The best thing for any wigger is a dose of TNB.

MY NIGGER SMELLS REALLY BAD

And you were expecting what?

WHERE SHOULD I STORE MY DEAD NIGGER?

When you came in here, did you see a sign that said " Dead nigger storage"? That's because there ain't no goddamn sign.

Re: Your official guide to the Jigaboo presidency. (-1)

Anonymous Coward | about 2 months ago | (#47726395)

You are a horrible person. This is also hilarious.

Re:Your official guide to the Jigaboo presidency. (-1)

Anonymous Coward | about 2 months ago | (#47726455)

That was pretty good, I lol'ed, bravo

Please Don't Feed The Trolls (-1)

Anonymous Coward | about 2 months ago | (#47728379)

Thanks.

Why can't hydrogen cool? (3, Interesting)

ShanghaiBill (739463) | about 2 months ago | (#47726349)

From TFA:

The big bang produced only hydrogen, helium, and a little lithium, and gas clouds containing only these elements can't cool.

Can someone please explain this? What would prevent a cloud of primordial elements from cooling?

Re:Why can't hydrogen cool? (1)

Grow Old Timber (1071718) | about 2 months ago | (#47726401)

It burns and can't condense(cool?)

Re:Why can't hydrogen cool? (4, Informative)

tysonedwards (969693) | about 2 months ago | (#47726405)

It's deceptive. At this point in time, the universe was quite small relatively speaking. As such, the density of those materials was still sufficiently high that the materials were in a persistent plasma state even though they weren't a "star", however fusion was still taking place converting Hydrogen to Helium. At this point, we're talking about all matter in the Universe occupying something not much larger than the Milky Way after all, maybe a little larger considering that we're talking about very, very fast expansion of the universe and the difference of a second amounts to a light year or so of growth. As the Universe continued to expand outwards and the material became less dense, it allowed for the material to actually split apart from one giant clump of hydrogen, helium and lithium and begin to actually get some empty space. As that empty space formed, then this plasmatic cloud could coalesce into the first stars. As long as there was these plasma clouds and not "empty space", then yes, there was "nothing" yet in which the material could *cool* into.

Re:Why can't hydrogen cool? (5, Informative)

ShanghaiBill (739463) | about 2 months ago | (#47726459)

I appreciate your explanation, but honestly, what you say makes no sense. To be blunt, I don't think you know what you are talking about. You say that the Universe was the size of the Milky Way, and expanding by a light year per second. Since the Milky Way is only 120,000 light years across, if the Universe was really expanding that quickly, it would be bigger than the Milky Way in ONE DAY. You also say that hydrogen fusion was occurring, but according to this graph [wikipedia.org] , fusion stopped three minutes after the big bang. There is nothing that you say that would only apply to H-He-Li and would not apply to heavier elements.

I found the following explanation here [harvard.edu] :

Hydrogen and helium are, by far, the most abundant elements in interstellar clouds. However, these elements are very poor coolants because they cannot be collisionally induced to emit photons at the low gas temperatures characteristic of molecular clouds. Two decades of theoretical studies have consistently predicted that a large fraction of the total cooling is borne by a few other atoms and molecules, notably gaseous water (HO), carbon monoxide (CO), molecular oxygen (O), and atomic carbon (C).

Re:Why can't hydrogen cool? (1)

mdsolar (1045926) | about 2 months ago | (#47727767)

You've got this right. Rotational transitions are the important ones (aside from atomic carbon). For molecular hydrogen, these are at higher energy so the most abundant molecule does not contribute much to radiative cooling normally. It does become important in primordial gas, but then the gas has to be warmer to excite those transitions.

Re:Why can't hydrogen cool? (-1)

Anonymous Coward | about 2 months ago | (#47728099)

Too bad Phil Plait wasn't around to answer some of these questions more intelligently... he only comes around when he's pimping himself and doesn't care about informing the ignorant. It's all about the dollars with Phil.

"expanding by a light year per second" (1)

mrops (927562) | about 2 months ago | (#47728633)

Further how is this possible, if the speed of light is absolute... well you can't move matter more than 1 light second in one second and that too requires infinite enregy, no?

Re:"expanding by a light year per second" (1)

Anonymous Coward | about 2 months ago | (#47728727)

Matter wasn't moving that fast; space itself was expanding that fast.

Re:"expanding by a light year per second" (1)

ShanghaiBill (739463) | about 2 months ago | (#47731043)

Matter wasn't moving that fast; space itself was expanding that fast.

Except that the super luminal inflation of space was over 1e-32 seconds after the big bang. I doubt if many stars were forming in that trillionth of a trillionth of a billionth of a second.

Re:"expanding by a light year per second" (2)

HiThere (15173) | about 2 months ago | (#47732259)

You sure about that? I was under the impression that it was probably STILL expanding faster than light, if measured from edge to edge (which, of course, you can't do, but can only calculate). In fact I was under the impression that it was believed that many areas of the universe may still be rapidly inflating, just not around here.

FWIW, (and in my understanding) there are theoretical reasons to believe that inflation will continue forever. They're just beyond our light cone. Perhaps this "problem" has been generally agreed to be resolved, but if so I haven't heard about it.

OTOH, I am not a cosmologist.

Re:Why can't hydrogen cool? (1)

mmell (832646) | about 2 months ago | (#47726553)

I know that hyperexpansion is the most widely accepted theory these days to account for our observations of the Universe's size, density and composition, but it is not universally accepted and (for obvious reasons) not proven - at least not yet.

I personally have doubts. After all, we can't observe the "edge" of the Universe now, only where the "edge" was some fourteen billion years ago. That "light cone" problem also sorta puts a damper on how detailed an observation we can make. Not saying it's a bad theory, just that I'm having a hard time seeing how it's falsifiable. Besides, everyone knows it's turtles all the way down . . .

Re: Why can't hydrogen cool? (0)

Anonymous Coward | about 2 months ago | (#47726959)

also at this early time isnkt the matter vs antimatter effect being overlooked?

Re: Why can't hydrogen cool? (1)

mdsolar (1045926) | about 2 months ago | (#47728549)

No, that was happening much earlier. Antimatter in the form of positrons is important in the pair instability though.

Re: Why can't hydrogen cool? (0)

Anonymous Coward | about 2 months ago | (#47726411)

I am not an astronomer.

The wording in this article seems really odd to me. The science also sounds dubious at best.

Any matter in the universe should cool down and not require heavier elements to do so.

It's possible that this article was trying to talk about the very early universe when things were still really hot and hadn't had much time (relatively speaking of course) to actually cool off.

Re:Why can't hydrogen cool? (0)

Anonymous Coward | about 2 months ago | (#47726415)

gravitational attraction, condensation and the eventual ignition of fusion all generate heat in these clouds.
not to mention that the universe was really REALLY fuckin hot for millions of years after the big bang, so it is technically correct, if awkwardly phrased.

Re:Why can't hydrogen cool? (3, Interesting)

mmell (832646) | about 2 months ago | (#47726527)

It can - now. Back then, where would the heat go . . . out of the Universe?

Re:Why can't hydrogen cool? (0)

Anonymous Coward | about 2 months ago | (#47727455)

That's a bit obtuse. Unless someone or other opened a window the heat still cannot escape from the universe.

Re:Why can't hydrogen cool? (1)

mmell (832646) | about 2 months ago | (#47731911)

Congratulations on demonstrating an understanding of the first law of thermodynamics.

Re:Why can't hydrogen cool? (2)

mdsolar (1045926) | about 2 months ago | (#47728129)

The universe cools as it expands. Once the background radiation is cool enough then the heat of contraction can dissipate. Initially, growth of structure in the universe happens only in dark matter because the normal matter smooths out destiny fluctuations. But after recombination, the normal matter begins to catch up. http://books.google.com/books?... [google.com]

Re:Why can't hydrogen cool? (1)

mmell (832646) | about 2 months ago | (#47731935)

Technically - the local temperature drops, the Universe has as much "heat" now as it had in the instant after the big bang. A lot of that energy is presumably tied up in the quantum foam, but none of that heat has left the Universe - unless the Universe has sprung a leak.

Re:Why can't hydrogen cool? (1)

HiThere (15173) | about 2 months ago | (#47732309)

Well, that's the current theory, but I still have trouble accepting dark matter. Perhaps they'll actually find some soon. It *does* fit with the math, so it's easy to understand why it's been proposed and believed in, but "believed in" feels more appropriate for religion than for science. I'll grant that it's the best current theory, but until they actually catch some, or explain why they can't in a convincing way, I'm going to remain iffy about it.

Re:Why can't hydrogen cool? (1)

david_thornley (598059) | about 2 months ago | (#47733311)

I don't understand,. I have no difficulty in believing there might be something like slow, heavy, neutrinos. If I didn't know about neutrinos, dark matter would sound more dubious.

Re:Why can't hydrogen cool? (1)

HiThere (15173) | about a month ago | (#47736533)

If they find "slow, heavy, neutrinos", then I'll believe them. Now I just think it makes sense to look.

Re:Why can't hydrogen cool? (1)

Vitriol+Angst (458300) | about 2 months ago | (#47732075)

Where does the heat go NOW? It's a closed system (as far as we know).

Heat is energy, and it's either going into matter or more energy. So it becomes more Complex.

However, we have more Space -- so it's better to say that "heat has diffused, or become a more complex interaction." For instance, if all force at one time went in one direction, it "seems" like there is less energy if there is equal and opposing force. Also, is all particles in a system are headed in one direction - they still have force, but the energy seems to "be at rest" relative to that system. At least if we keep things in a Newtonian Universe.

I think however, that much of the energy has "sublimated" -- or is at a frequency we don't interact with. Like what is called quantum fluctuations or "vacuum energy". The "cold matter" we interact with, has a much lower frequency and so rides on top of a lot of the energy (like a carrier wave) that existed from the Big Bang. Not sure if that is accepted theory, but it's the obvious answer that springs to mind if I'm sticking with a General Relativity Universe.

To think about it is kind of awesome; right now, there is as much energy and activity as when the Universe first "exploded" into existence -- however, I theorize we have a 12 dimensional Universe, so a lot of the energy is being traded to a subset of 4 dimensions while we "appear" to have more empty space. The side effect of this interaction produces what we call gravity. However, that's just my theory, but it seems more simple than the other models. ;-)

Re:Why can't hydrogen cool? (2)

stevelinton (4044) | about 2 months ago | (#47727565)

Basically the conditions (temperature, density, amount of ionizing radiation around) thought to apply, the gas would be made up of atoms that tend to simply bounce off one another when they collide. This doesn't change the total energy in random motion of the cloud, ie the temperature.

More complex atoms or molecules can interact in more complicated ways when they collide, so that part of the energy ends up as vibration in a molecule, or extra energy of an electron in an excited state. These vibrating molecules or excited atoms then relax back to their ground state releasing a photon and so actually cooling the cloud.

Re:Why can't hydrogen cool? (1)

bigsexyjoe (581721) | about 2 months ago | (#47728805)

The article doesn't say they couldn't cool in the conditions of the early universe, it says such a cloud could never cool.

I'm not a chemist, but I would guess it's because the electrons cannot fall to a lower energy state, which converts heat to radiation. Since the heat is not radiated, it stays heat inside the cloud.

Or the article gets the details wrong...

Re:Why can't hydrogen cool? (1)

Vitriol+Angst (458300) | about 2 months ago | (#47731993)

To explain this, not only will the Higgs Boson be created to explain away the aether, and Dark Matter to explain why there's more gravity at a distance than up close, but now we need learn that particles cannot cool unless they are affected by the "Snoop Dog" field.

Re:Why can't hydrogen cool? (1)

HiThere (15173) | about 2 months ago | (#47732383)

You're being silly. There are good reasons that the clouds of hydrogen couldn't (easily) cool, and they remain true today. Of course these days the clouds are "polluted" with various heavy elements which radiate well and allow the clouds to cool relatively easily. (Even under current condition radiative cooling is rather inefficient.) Hydrogen just has a hard time radiating. It can, a little bit, but not very well. If the cloud is too hot, there aren't any bound electrons, so you don't even get the current (poor) radiation that hydrogen can provide, because radiative cooling depends on an electron slipping from an excited state to a non-excited state, and emitting a photon in the process.

I trust you don't want me to go on.

Re:Why can't hydrogen cool? (1)

Anonymous Coward | about 2 months ago | (#47732537)

In order for a particle to cool it either needs to collide with another particle, which is cooler, so that it can transfer kinetic energy to it, or it needs to have electrons in unstable (high energy) orbits so that it can release photons when the electron returns to a lower energy state. Back in those days the molecular hydrogen was really hot, so hot it couldn't even hold on to it's electrons (a plasma) and collisions with other hydrogen atoms would not have reduced the kinetic energy of those atoms, so the temperature of the cloud remains unchanged. Increasing the volume of the cloud would cause cooling but gravity was trying to do exactly the opposite.

As the article points out, it takes a whopping big cloud of hydrogen plasma for it's gravity to overcome it's outward pressure due to temperature.

Population II stars and globular star clusters (2)

torsmo (1301691) | about 2 months ago | (#47726453)

Why are they present mostly in the galactic halo? Also, stars like SM0313 are supposed to have formed only a 100mn or so years after the Big Bang. Is that enough time for Population III stars to have formed and gone supernova?

Re:Population II stars and globular star clusters (1)

mmell (832646) | about 2 months ago | (#47726515)

Something to do with how galaxies form?

Re:Population II stars and globular star clusters (1)

mdsolar (1045926) | about 2 months ago | (#47729211)

The question is more why are Population I stars mostly in the disk. The answer is that the disk formed later. The main sequence lifetime of massive stars is about a million years so there is not big timing issue related to that. http://en.wikipedia.org/wiki/M... [wikipedia.org]

I took this for granted (2, Interesting)

Anonymous Coward | about 2 months ago | (#47726995)

Big Bang -> a few ridiculously massive stars -> a few little Bangs -> many massive stars -> many hypernovae -> many many large stars -> many many supernovae -> ... -> ... -> Michael Bay

It's explosions all the way down.

All the gold (1)

invictusvoyd (3546069) | about 2 months ago | (#47727399)

Is ancient ! .. All that gold !!!

It's called "theory" for a reason (0)

osiaq (2495684) | about 2 months ago | (#47727861)

It's called "theory" for a reason

Re:It's called "theory" for a reason (1)

cupantae (1304123) | about 2 months ago | (#47729269)

It's called "theory" for a reason

Because that's the word that has come to represent the meaning of the word "theory"?
I'm sorry, I can't work out what point you're trying to make.

Re:It's called "theory" for a reason (1)

Bob_Who (926234) | about 2 months ago | (#47730303)

It's called "theory" for a reason

Because that's the word that has come to represent the meaning of the word "theory"? I'm sorry, I can't work out what point you're trying to make.

I think it might be circular logic, which might suggest a closed universe (and reruns).

Its like deja vu all over again.

I just want to bang, bang, bang!

Re:It's called "theory" for a reason (1)

HiThere (15173) | about 2 months ago | (#47732453)

He's probably expecting that if we were sure about it we'd call it a law. He's ignoring the game-rule of science that says you should never be sure anything is correct. All you can do is prove things wrong. And if there's no way to test whether it's wrong it's meaningless. (This is not the same as, and does not imply, "if there's no additional way to test whether it's wrong it's meaningless.")

Re:It's called "theory" for a reason (1)

cupantae (1304123) | about a month ago | (#47736023)

Yeah, but without even referencing the theory that's supposedly conjecture.
What lazy idiocy.

Pair-instability Supernovae (2)

Rich0 (548339) | about 2 months ago | (#47728211)

So, I don't get why pair-instability supernovae happen in the first place, and the Wikipedia article certainly isn't helping.

The argument is that at some point a star gets hot enough that its photons start creating electron/positron pairs, and this causes a collapse. Then that collapse leads to a runaway nuclear reaction.

What I don't get is how the star would ever become supercritical from a nuclear reaction perspective. I get that there might be some kind of transition in pair creation as the whole star gradually increases in temperature and perhaps a large portion of the star crosses some threshold temperature at the same time. I get that this could reduce pressure in the star and allow it to start collapsing.

However, while the transition in pair-creation behavior might happen quickly (this is an event at the quantum level), the collapse of the star involves huge masses of gas falling inwards at macroscopic speeds. I don't see how the migration of a few dozen sun's worth of H/He towards the core is going to happen at a rate anywhere near the rate at which individual H/He atoms are colliding throughout the core. So, if the density started to rise such that you got an increase in nuclear reactions, wouldn't that create additional pressure that stops the collapse?

For there to be an explosion you need to build up potential energy of some kind and then release it all at once. If you light C4 with a match it just burns from the surface which doesn't lead to a dramatic release of energy. If you send a shockwave through it that travels faster than the speed of sound in the medium then the initiation of combustion of the C4 propagates faster than the shock wave produced by the combustion, and as a result the energy of the entire explosive is released seemingly at once. Likewise if you ignite a cloud of pure hydrogen surrounded by normal air it will just burn at the surface hotly, but if you premix hydrogen and air to a stoichiometric mix and light a match, it will detonate, because in that case the ignition will naturally propagate faster than the speed of sound (and is not limited by the diffusion of oxygen/hydrogen to allow mixture).

Nuclear reactors don't explode, because they aren't significantly supercritical - they stay near equilibrium. A nuclear bomb reaches supercriticality because for a very short moment in time the inertial of the collapsing fissile mass allows it to continue to collapse before the energy produced by the initiating chain reaction can blow it apart.

Is that the case for these supernovae? Does it take long enough for the nuclear reactions to start that the mass of the falling gas has enough inertia to allow it to continue to compress even after passing the critical point?

Re:Pair-instability Supernovae (0)

Anonymous Coward | about 2 months ago | (#47729907)

I think you've got it: after pair-creation suddenly decreases the pressure, the outer layers of gas acquire considerable momentum, falling in towards the centre of the star, before the fusion rate starts dramatically increasing. That momentum keeps the core compressed long enough for fusion to release a lot of energy, before that energy eventually reverses the momentum and blows the outer layers of the star away.

The article [harvard.edu] that another replier linked seems to mostly take this implicitly rather than stating it outright, but the following passage makes it fairly clear:

More massive stars with higher entropies become unstable at lower temperatures. During the collapse they acquire a greater inward momentum, and reach a higher temperature at the reversal of collapse. There is a greater energy release from the oxygen burning, and so the explosion following the collapse is of greater intensity.

(In this case, "oxygen burning" means the nuclear reaction that occurs is oxygen-oxygen fusion.)

As you pointed out, this is analogous to what happens in a nuclear bomb: the inward momentum of the fissile material (and sometimes also a heavy "tamper" designed for this purpose), driven in this case by explosives rather than by gravity, keeps the fissile material confined long enough for a lot of fission to take place.

Pair Instability Super Novae (2)

mdsolar (1045926) | about 2 months ago | (#47728345)

The instability that causes the collapse of a stellar core and subsequent explosion comes from turning gamma rays into pairs of electrons and positrons. This turns energy into matter and cuts the pressure that the energy provides. http://en.wikipedia.org/wiki/P... [wikipedia.org] It turns out that these explosions may make observing the early universe easier. One of the most important abundance ratios is the interstellar medium is the ratio of oxygen to carbon. The strength of the carbon monoxide bond is so strong that these two really pair up. Whichever runs out first determines the remaining chemistry to a large degree. Mass losing carbon rich stars produce carbon rich dust, while mass losing oxygen rich stars produce silicate dust for example. But, primordial Pair Instability Super Novae may produce lots of oxygen with little carbon or silicon to combine with. So the very early solid phase of the ISM may be mostly water ice. This happens to increase the far infrared emissivity of this solid phase making early objects brighter in the red-shifted sub-millimeter. Thus very early object may be easy to find in surveys at that wavelength. http://iopscience.iop.org/0004... [iop.org]

I got you one better, Mr. Fancy Pants Ancient Star (0)

Anonymous Coward | about 2 months ago | (#47728655)

The atoms that make up my body were created in the Big Bang itself, and half of them, statistically, were once antimatter.

Re:I got you one better, Mr. Fancy Pants Ancient S (1)

mmell (832646) | about 2 months ago | (#47731971)

Not quite. If yon atom is heavier than lithium, it's a fair bet it wasn't created until well after the big bang.

Now, the quarks making up those newfangled heavy atoms - those have been around since the beginning.

Best Title (0)

Anonymous Coward | about 2 months ago | (#47729067)

This is the best title of a Slashdot news story to be repurposed as the title of a rock song.

Block Holes? (1)

MrL0G1C (867445) | about 2 months ago | (#47731341)

I thought 'extremely massive' stars were supposed to end up as black holes when they collapsed?

Re:Block Holes? (1)

mdsolar (1045926) | about 2 months ago | (#47731715)

At low metalicity there is a range of stellar mass where the star is completely disrupted. Look at slide 36 here: http://www.mpa-garching.mpg.de... [mpa-garching.mpg.de]

Re:Block Holes? (1)

mmell (832646) | about 2 months ago | (#47731983)

No, a lot of them just end up on the talk show circuit.
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