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    15 Aug '19 16:091 edit
    https://phys.org/news/2019-08-total-annihilation-supermassive-stars.html

    Not long ago, it was not known if such supermassive stars could actually exist as they were merely theorized. But now it appears they do. What makes this type of supernova from the explosion of supermassive stars interesting is that, unlike other supernova from explosion of supermassive stars, this type results in the WHOLE of the star being blown completely apart outwards thus INCLUDING its core, thus leaving no black hole or neutron star remnant behind.
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    16 Aug '19 20:571 edit
    My above misedit;
    "Not long ago, it was not known if such supermassive stars..."
    should be
    "Not long ago, it was not known if such pair-instability supernovae from exploding supermassive stars..."
  3. Subscribersonhouse
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    16 Aug '19 23:09
    @humy
    Do they have any idea on how that could happen? I wonder if it was just an 'ordinary' supernova that just blew its remains away like with an asymmetric explosion or some such where the core is now light years away from the explosion site.
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    17 Aug '19 06:082 edits
    @sonhouse said
    @humy
    Do they have any idea on how that could happen? I wonder if it was just an 'ordinary' supernova that just blew its remains away like with an asymmetric explosion or some such where the core is now light years away from the explosion site.
    I certainly don't pretend to understand the physics on the particle level but, no, the core isn't light years away from the explosion site because, unlike in a normal supernova, the effect of what happens in the core on the particle level is to make the core explode outwards so to cease to exist (as a core) rather than to make it implode. The core itself thus, unlike in a normal supernova, becomes just part of the highly dispersed expanding gas/ions from the explosion i.e. just part of the nebula.
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    17 Aug '19 12:51
    @humy said
    I certainly don't pretend to understand the physics on the particle level but, no, the core isn't light years away from the explosion site because, unlike in a normal supernova, the effect of what happens in the core on the particle level is to make the core explode outwards so to cease to exist (as a core) rather than to make it implode. The core itself thus, unlike in a normal ...[text shortened]... ust part of the highly dispersed expanding gas/ions from the explosion i.e. just part of the nebula.
    The energy of gamma rays in the core depends on the core's temperature. If the core is hot enough the energy of the gamma can exceed twice the mass of an electron which allows pair production. The electron positron pair does not generate the pressure the photon did so the core shrinks. This causes it to heat more. If the process runs away the entire core can undergo fusion in something of the order of a second releasing enough energy to gravitationally unbind the star. I think it happens as a result of the star getting hotter as it burns fuel - as is the sun.
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    17 Aug '19 12:521 edit
    @sonhouse said
    @humy
    Do they have any idea on how that could happen? I wonder if it was just an 'ordinary' supernova that just blew its remains away like with an asymmetric explosion or some such where the core is now light years away from the explosion site.
    I think in most cases the nebula looks asymmetric as a result and they can search for the remnant. Since pair instability supernovas do not leave a remnant eliminating this possibility would be part of justifying the claim.
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    17 Aug '19 14:31
    @DeepThought
    I guess they can work out how old the nova event is and then figure out the maximum sphere in which to find a rogue core.
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    @sonhouse said
    @DeepThought
    I guess they can work out how old the nova event is and then figure out the maximum sphere in which to find a rogue core.
    Assuming they can get a distance measurement they can work out the size of the nebula and do a calculation to get an estimate of how long ago the event was, which gives them a sphere to search in. Since the remnant isn't necessarily luminescent they may be relying on gravitational anomalies. Finding a remnant rules out a pair instability supernova. Not finding a remnant just means we haven't found a remnant. What doing the search does is check there isn't an obvious alternative explanation that they should have seen rather than guarantee that they've got it right.
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    23 Aug '19 18:07
    @DeepThought
    It is hard to see how gravitational anomalies would help find a rogue core when it would be light years from the nearest object except the nebula that spawned it.
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    23 Aug '19 23:41
    @sonhouse said
    @DeepThought
    It is hard to see how gravitational anomalies would help find a rogue core when it would be light years from the nearest object except the nebula that spawned it.
    I think the main way they're detected is by X-ray emissions. There's about 10 million stars within a light-year of Sagittarius A* so near the Galactic bulge it's plausible neutron stars or black holes could be detected by gravitational anomalies.
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    24 Aug '19 13:12
    @DeepThought
    By gravitational anomalies I assume you mean a shift in the orbit or course of movement of some star under the influence of said missing core.
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    24 Aug '19 18:32
    @sonhouse said
    @DeepThought
    By gravitational anomalies I assume you mean a shift in the orbit or course of movement of some star under the influence of said missing core.
    That's correct. This is way off my field, I don't know how difficult it is, however I think it's possible at a statistical level - the instantaneous velocities don't make sense given the rest of the visible matter.
  13. Subscribersonhouse
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    08 Sep '19 19:31
    @DeepThought
    Hey Deep Thought, your computer finally gave the answer for 42😉

    https://www.sciencedaily.com/releases/2019/09/190906134011.htm

    Funny how Adams used a number that turned out to be the hardest one to solve for the sum of 3 cubes problem!
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