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Neutron Star Contemplation

  1. Mar 14, 2014 #1
    Hi everyone!

    First of all, I'm a brand new member and am looking forward to spending time on this forum, learning a bit more about science, and getting to know some of you.

    Anyway, here's what's been on my mind lately:

    I've heard that a thimbleful of neutron star material weighs as much as a mountain does on Earth, so I've been wondering...

    Scenario: Two neutron stars collide with each other and a thimbleful of material is ejected from the system onto a collision course with Earth.

    1) As the thimble sized chunk of material leaves the neutron star system, does it remain thimble sized, does it grow to be mountain sized, or does it explode into a mountain's worth of little bits of matter? In other words, is the matter capable of returning to a normal state after being subjected to such intense forces?

    2) If the material remains the size of a thimble, will it burn up in Earth's atmosphere, like other rocks of that size? Or, would it do damage to Earth as if it were mountain sized?

    Note: My formal education in science amounts to a 4 credit hour physics course, which was required for my accounting degree, so bare with me. I'm well aware that this question could be silly and/or meaningless, but I hope it's not.

    Last edited: Mar 14, 2014
  2. jcsd
  3. Mar 14, 2014 #2


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    Welcome to the forum.

    Not bad questions at all. I'm no expert on this but I do recall that there was a discussion of neutron star material and I'm pretty sure I recall the answer being that if magically transported away from the neutron star, a chunk of material would explode because of the sudden release of the ENORMOUS pressure that it is under.

    That being the case, the question about what it would do to the Earth doesn't apply, BUT ... you could consider a very small black hole of similar size (and big enough not to evaporate quickly, which the little ones do) hitting Earth.

    The result would be very similar to the answer reported by Mark Twain as having been given by a sea captain when a dowager spotted an iceberg in the distance and asked the captain what would happen if the ship collided with it. The captain thought for a moment and then said very gravely "The iceberg, madam, would continue onward as though nothing had happened".

    With any significant speed, the mini black hole would just keep on going. If you posit a very slow speed or a slightly bigger black hole, then it would probably oscillate in and out of the Earth, turning the earth into Swiss cheese, followed by no cheese at all.
  4. Mar 15, 2014 #3


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    The normal thing for neutrons to do, if not bound in a nucleus or under huge gravitational compression, is to radioactively decay.

    For example an isolated neutron might decay into a proton and an electron (with some extra radiation).

    Or four neutrons might spit out 2 electrons and remain a positive charged helium nucleus (two protons and two neutrons bound in a stable configuration)

    You could look up "neutron" in Wikipedia and learn about the ways neutrons can decay and how quickly they do it if not bound with roughly equal numbers of protons in some stable combination like an atomic nucleus

    Also Wikipedia would say how rapidly they decay. (quite quickly, like 15 minutes)

    To more directly answer I personally would guess that if two neutron stars collide there would be a larger neutron star (or black hole) plus a lethal hot gas cloud of RADIOACTIVE DEBRIS.

    I guess you would NOT see intact chunks of neutron matter flying out from the collision, any debris would not be neutron matter because that would not be stable, it would already have decayed into electrons and (often radioactive) ordinary-matter-type nucleuses. No intact chunks but a big hot mess.
  5. Mar 15, 2014 #4
    A chunk wouldn't be ejected. If it did, it would explode immediately. It contains great pressure, so once the pressure is released it would explode.

    Let's suppose it somehow stays intact. It would penetrate the Earth's atmosphere as a meteor. The surface area is quite small, so not all that much heat would be generated. It would strike the Earth and pass through as though it were nothing. I think there would not be much disturbance. A thimble can't do much damage.

    If it somehow exploded inside the Earth that would be cataclysmic.
  6. Mar 15, 2014 #5
    phinds, this makes a lot of sense to me. Thanks for your input.
  7. Mar 15, 2014 #6
    That´s the only thing it can do.
    They´d need to be together somehow.

    Dineutron is not a bound state. And neither is hydrogen 4.

    Large amounts of neutrons should mainly decay to tritium. Unless there is some source of nuclei with at least 9 nucleons... in which case rapid beta decay along neutron drip like should go to over 200 nucleons.
  8. Mar 16, 2014 #7


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    It's believed that decompressed neutron star material expands (explodes) into ordinary matter which is composed of heavy neutron-rich elements. In fact, many astrophysicists believe that most of the elements here on Earth heavier than iron (gold or uranium for example) were produced from decompressed neutron star material that was ejected when two neutron stars coalesced to form a black hole. Try looking up this paper, for starters.
  9. Mar 16, 2014 #8

    It would seem to me that such a process is too rare to account for the observed amount of heavy metals. I thought that they came from supernovas. But who knows?
  10. Mar 16, 2014 #9


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    Estimates of the rate of neutron star mergers vary a lot, but it seems like 10 mergers/million years in a galaxy like the Milky Way is a reasonable estimate. We already know of at least three binary neutron stars that will merge in the next few billion years, and we only have surveyed a tiny fraction of the galaxy. Also, it is believed that short Gamma Ray Bursts are produced by neutron star mergers, and we see short GRBs every day (although we are sampling a very large number of galaxies). Since the Milky Way is ~10 billion years old, there have been perhaps 100,000 of these mergers. It's clear that the elements up to iron are produced in supernovae, but there is currently a lot of debate as to whether there is enough production of the elements heavier than iron to account for the observed abundances. The neutron star hypothesis has been advanced as an alternate hypothesis for the production of these elements. Which is correct remains to be seen.
  11. Mar 16, 2014 #10
    Don't underestimate the amount of material ejected, either. I suspect the numbers are "staggering".
  12. Mar 16, 2014 #11


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    Not really. The paper I linked earlier has run simulations of neutron star mergers and concluded that for each merger, between 4E-2 and 4E-3 solar mass of neutron star material is ejected into space. Taken together with the merger rate, this is at least the right order of magnitude to explain the abundances of the heavy elements.
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