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B The lifespan of a neutron star

  1. Mar 24, 2016 #1
    How durable are the neutron stars, ie how long can they last? Will they "evaporate" like black holes or something else will happen with them after a very long period of time (eons)? Or are they immortal?
    I'm asking because I have found nothing clear about the lifespan of a neutron star.
     
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  3. Mar 24, 2016 #2

    jedishrfu

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    Here's more info than you'd ever want to know informally about a neutron star:

    https://www.astro.umd.edu/~miller/nstar.html

    and from this NASA website an estimate 10 billion years for some oldest known pulsars:

    http://imagine.gsfc.nasa.gov/ask_astro/neutron_star.html

     
  4. Mar 24, 2016 #3

    Ken G

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    I don't think there's any known physical process that would make the neutron star last for less time than an infinite time. Of course, a lot can happen in infinite time.
     
  5. Mar 25, 2016 #4
    Nothing can last forever, not even the Universe, so I doubt that a neutron star could have an infinite lifespan. A physical process that could make a neutron star to last for less than an infinite time could be the quantum tunneling.
    Are there are some theoretical estimates for the lifespan of a neutron star?
     
  6. Mar 25, 2016 #5

    Ken G

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    No known physics could come up with a reasonable timespan that we could have any confidence in.
     
  7. Mar 25, 2016 #6

    Chronos

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    The most ancient known star is a type K dwarf star called SMSS J031300.36- 670839.3, with a confirmed age of 13.6 billion years - re:http://arxiv.org/abs/1402.1517. As neutron stars go they are extremely faint and difficult to detect - and even harder to to assign a reliable age. Pulsars can be detected much further out, but, pulsars spin down and lose the ability to 'pulse' [hence become undetectable] in relatively short order. The slowest known pulsar in J2144-3933 with an amazingly long period of 8.5 seconds. It is estimated to be about 34 million years old. In theory a neutron star should outlive any other type of star. So the oldest neutron star is probably at least as old as the oldest known star, or nearly the age of the universe.
     
  8. Mar 25, 2016 #7
    I think neutron stars are as close to immortal heavenly bodies as one might hope to find. They won't evaporate, as far as I know. They could accumulate enough mass to collapse into a black hole. They could collide with a white dwarf, neutron star, or black hole. These are rare events. Outside of that, they would go on forever.
     
  9. Mar 26, 2016 #8
    Neutron stars, white dwarfs, planets are all stable. They all only cool with time and on the scales of ~100 billion years all activity such as thermal light emissions, geology, quakes on them stops. A relatively small residual magnetic field may remain.

    They may be not infinitely stable if nucleons are unstable ("proton decay", also affects neutrons despite its name).
     
  10. Mar 27, 2016 #9
    I'm pretty sure they have about a 10 billion year lifetime. They might collapse and form a black hole, the star would have to have at least 25 solar masses in order for it to successfully form a black hole.
     
  11. Mar 27, 2016 #10

    mfb

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    Every collection of matter will evaporate, assuming the universe continues to expand at an exponential rate. The expansion leads to a background temperature of about 1/(16 billion years) in natural units, or 10-28 K - order of magnitude estimate. At this temperature, it is extremely unlikely that thermal fluctuations kick out an electron or an atom of a neutron star - but it will happen, and over ridiculously large timescales (something like 101040 years) neutron stars will evaporate.

    If protons are unstable, then neutron stars will evaporate much faster due to hadron decays.


    This is not their lifetime, it is a lower bound on the maximal lifetime.
     
  12. Mar 27, 2016 #11

    Ken G

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    Extrapolating physics theories vastly beyond the regimes in which they have ever been verified is one technique for learning about our physics theories, but has a poor track record as a means of learning about what actually happens.
     
  13. Mar 27, 2016 #12
    This would violate conservation of energy: the mass of neutron star is 20% less than mass of all its neutrons (and other lesser constitutients) when they all are pulled away and are "free particles".

    Temperature fluctuations are just statistical behavior of large collection of randomly moving particles. In some cases statistical approximation is not exact enough.

    Here, at very low temps, when combined kinetic energy of all particles in the body is less than what you need to kick out even one neutron from neutron star to infinity, neutrons no longer can escape.
     
  14. Mar 27, 2016 #13

    mfb

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    You have the energy - it is coming from the cosmological expansion. There is no global conservation of energy in general relativity anyway.
    Something else might happen before, but unless that destroys the neutron star (which does not change the conclusion), a lot of time and exponential expansion (=assumptions I made) are sufficient.
     
  15. Mar 27, 2016 #14
    2 solar mass NS contains about 3*10^57 neutrons. To escape from NS, single neutron needs ~200 MeV of kinetic energy. When temperature of NS falls below ~ 10^-44 K, total kinetic energy of all neutrons in the NS is not enough to give 200 MeV to a single one. If NS can get that cold, then it will be absolutely stable against thermal evaporation.
     
  16. Mar 27, 2016 #15

    mfb

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    It won't get that cold with current cosmology.

    Also, you still have the environment which also has fluctuations.
    The surface has normal atoms, so you would start by removing those. Would give an interesting object.
     
  17. Mar 28, 2016 #16

    Ken G

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    The number 101040 years came up. My money says that the time it takes up to come up with a new expectation about what will happen to the universe in the next 101040 years is a whole lot less than 101040 years. But we can still talk about what our current theories say.
     
  18. Mar 29, 2016 #17

    mfb

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    ALL our statements are always "within the current theories". And speculations beyond current theories are against the forum laws anyway.
     
  19. Mar 29, 2016 #18

    Ken G

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    The issue is whether or not we have any good reason to expect our current theories to be right. Usually, we are working within some observational framework that can give us confidence. I don't think that's the case when numbers like 101040 years come up. It's the same issue with the general gedankenexperiment concept-- we confuse what empirical science is if we think gedankexperiments are experiments. They are only ways to talk about a theory, nothing more. Our shooting percentage drops rapidly the farther we leave behind the realm of experiments we have actually performed.
     
  20. Mar 31, 2016 #19
    Yes - neutrons undergo beta-decay near the surface; the weak interaction reverses the decay only at very high pressures of the interior. So neutron star have coronas with degenerate electron matter and outside that still lower density with ionized matter. A weak stellar wind would be offset by infalling atoms from nearby space.

    A remnant magnetic field would diffuse outwards, because the back-and-forward weak interactions cause diffusion of the otherwise 'frozen-in' field. Very low activity levels, but the neutron star is not absolutely 'dead' to the universe.
     
  21. Mar 31, 2016 #20

    Ken G

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    The problem with a neutron star having a wind (after it has spun down) is that it is energetically disfavored. Degenerate matter that loses mass must expand, so the gravitational potential energy must increase (it must go to smaller magnitude, but it is negative). So energy must be added to both the lost matter in the wind, and also everything that stays behind, and this will soon become impossible. Making matters worse is that both beta decays, and the inverse weak interaction, both result in the emission of neutrinos (the Urca process), so escape of those neutrinos would produce yet another energy loss channel. With all these energy losses going on, there will come a point where the wind too must die. Ultimately, neutron stars (and black white dwarfs) must be about the deadest objects we can imagine.
     
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