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Space

The Star That Exploded At the Dawn of Time 55

Posted by samzenpus from the in-the-beginning dept.
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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The Star That Exploded At the Dawn of Time More

The Star That Exploded At the Dawn of Time

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  • Why can't hydrogen cool? (Score:4, Interesting)

    by ShanghaiBill ( 739463 ) on Thursday August 21, 2014 @11:44PM (#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?

    • It burns and can't condense(cool?)

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

      by tysonedwards ( 969693 ) on Friday August 22, 2014 @12:03AM (#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? (Score:5, Informative)

        by ShanghaiBill ( 739463 ) on Friday August 22, 2014 @12:22AM (#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).

        • 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.

        • 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: (Score:1)

            by Anonymous Coward

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

            • 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: (Score:3)

                by HiThere ( 15173 )

                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 b

      • Comment removed based on user account deletion

    • Comment removed (Score:4, Interesting)

      by account_deleted ( 4530225 ) on Friday August 22, 2014 @12:40AM (#47726527)
      Comment removed based on user account deletion
      • 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]
        • Comment removed based on user account deletion

        • Re: (Score:2)

          by HiThere ( 15173 )

          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.

          • 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: (Score:2)

              by HiThere ( 15173 )

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

      • 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

    • 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 molecu

    • 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...

    • 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: (Score:2)

        by HiThere ( 15173 )

        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 cu

    • Re: (Score:1)

      by Anonymous Coward

      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 t

  • 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?

  • I took this for granted (Score:2, Interesting)

    by Anonymous Coward

    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.

  • Is ancient ! .. All that gold !!!

  • Pair-instability Supernovae (Score:3)

    by Rich0 ( 548339 ) on Friday August 22, 2014 @07:45AM (#47728211) Homepage

    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?

  • Pair Instability Super Novae (Score:3)

    by mdsolar ( 1045926 ) on Friday August 22, 2014 @08:01AM (#47728345) Homepage Journal
    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 thought 'extremely massive' stars were supposed to end up as black holes when they collapsed?

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