Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Is proton decay considered in neutron star models (and LHC)?

  1. Jan 27, 2017 #1
    Although it is definitely not simple, there are many reasons to consider that baryon number can be violated, for example:
    - while baryogenesis there was created more matter than antimatter,
    - hypothetical Hawking radiation can finally turn any matter (mainly baryons) into massless radiation (photons),
    - some GUT models require proton decay: https://en.wikipedia.org/wiki/Proton_decay ,
    - while charge conservation is guarded by Gauss law, there is nothing like that for baryon number.

    Sure, the search for proton decay in huge room temperature water tanks was unsuccessful. However, if proton can be destroyed, it would require relatively huge energy – the assumption that it can spontaneously thermally localize on a single proton in room temperature water might be just wrong (?)
    In contrast, baryogenesis and Hawking radiation examples suggest that really extreme conditions would be necessary to destroy a proton (like temperature).
    So another candidate might be LHC, but if happening in tiny amounts, the calorimetry has no chance to catch it, and to consider it in Monte Carlo we would need the exact parameters … is proton decay considered for LHC?

    More important candidate as environment with the most extreme conditions is the center of neutron star.
    There are real issues with understanding the huge amounts of energy released in gamma-ray bursts – from Wikipedia: “The means by which gamma-ray bursts convert energy into radiation remains poorly understood".
    Or ultraluminous X-ray sources, especially the M82 X-2: pulsar radiating ~10 million times more energy than our sun.

    Hypothetically, reaching extreme conditions to start statistically essential “baryon burning” (total matter->energy conversion) in the center of neutron star, might help explaining these extreme energy sources.
    So I wanted to ask if proton/neutron decay is considered in neutron star models? Should it?
  2. jcsd
  3. Jan 27, 2017 #2
    If you add huge amounts of energy, then it's not really decay. Proton decay implies that protons are unstable when they're by themselves.

    Adding rediculously high pressure isn't forcing them to decay, it's simply crushing the protons. That's not decay, that's just being melted into their quark/gluon parts, which has been done at LHC and is predicted by QM. It's called a degenerate matter.
  4. Jan 27, 2017 #3
    The problematic/controversial(?) part of proton decay is violation of baryon number conservation, e.g.:
    proton -> positron + gammas
    this positron will annihilate, so finally we get total matter->energy conversion: mc^2 of energy, like for annihilation but without the need of antimatter, >100x larger energy density than from fusion.

    We probably just don't know if it is happening in LHC (?) - it seems very difficult to test (?)
    We assume that such violation of baryon number was happening during baryogenesis (just after Big Bang) and can happen in black hole through Hawking radiation as it effectively converts the (baryonic) matter into massless radiation (photons).

    From the perspective of star evolution, I have referred to it as "baryon burning" phase - hypothetical destruction of neutrons and protons in the center of neutron star, fully converting them into energy - releasing enormous amount of energy and preventing star from collapse.
    If possible, it would require reaching some really extreme conditions to destroy the structure of baryons in statistically essential rate - what might have essential consequences for models of neutron stars (?)

    The question is if such possibility is even considered in current models of neutron stars?
  5. Jan 27, 2017 #4
    Why would a positron annihilate? If the proton has decayed, that means that the proton is no longer there for the positron to react with.

    Neutron stars just aren't powerful enough. The forces can be calculated, and they simply don't reach the pressures needed to crush neutrons any further. Neutron stars also don't really have many protons in them, maybe a very thin layer of carbon atoms forming a crust, but mostly, it's neutrons. The protons have already been destroyed in this case.

    When a neutron star is formed, all of the atoms get crushed with such incredible heat and pressure that protons are no longer stable. That's a protons melting point, which is not the same as decay. Protons

    There are denser things than neutron stars (in theory,) so yes, the melting point of baryons is considered. A neutron star that is too massive will crush neutrons beyond their melting points too, which creates a quark-gluon plasma. Ill say it a different way: bayrons do not crush into pure energy, they just melt into their parts. These objects are called quark stars and they're even more extreme.

    You need to understand the equilibrium of neutron stars, it's not the same as normal stars. Normal stars are kept in equilibrium by the force of gravity pulling everything in, and the heat generated from nuclear fusion at the core. Neutron stars are completely different. The inward force is still gravity, but what keeps the neutron star from collapsing completely is neutron degeneracy pressure. When you overcome that with enough mass, then you can crush a little further until you run into quark degeneracy. If you create even more pressure and overcome that, then there is nothing that can stop gravity. We don't know what happens at such extreme energies that the elementary particles actually get crushed, but we know that no amount of energy can overcome the black hole that's formed.

    So there is questions about what happens to matter at energy densities of black holes, but neutron stars are low energy by comparison and perfectly within our ability to calculate.
  6. Jan 27, 2017 #5
    Positron annihilates with electron (not proton).
    Assuming total charge is zero, the summary of (hypothetical) proton decay would be total matter->energy conversion (mc^2):
    proton + electron -> positron + gammas + electron -> gammas
    neutron -> proton + electron -> gammas (and some neutrinos)

    Regarding not being powerful enough - so what are the minimal required conditions for destroying baryons (into pure energy) in statistically non-negligible way?

    Remember that some neutron stars are believed to collapse into a black hole.
    Such collapse means that surface fall below the event horizon, but event horizon should start growing from the center of star.
    Like here: http://www.astro.ucla.edu/~wright/bh-st.html - blue lines represent the star, purple line is event horizon:
    As Schwarzschild radius is proportional to mass, mass to rho*r^3, the formation of event horizon seems to require reaching infinite density first (r ~ r^3*rho, so for r->0 we have rho->infinity) - exceeding any eventual threshold for complete destruction of baryons (?) - not just into a quark soup, but into pure energy.

    So it seems before collapsing into a black hole, neutron star should undergo some baryon burning phase in its center?
  7. Jan 27, 2017 #6
    No, there are no electrons in neutron stars. Protons and electrons get crushed together (with some energy) to create the neutron degenerate matter. You are still under the impression that neutron stars have normal atoms in them, they don't. There are no protons, no electrons, nothing except neutrons. They did not decay into neutrons, they were melted into them.

    Secondly, a positron and an electron will almost certainly not destroy each other in space. They have the same charge, and will repel each other.

    Neutron stars to do collapse into black holes, there are no theories that say that. You need something to trigger that (like two of them merging.) A big star dying, will not become a neutron star, it'll just blow right past that and collapse into a black hole directly.

    As for how much power it would actually take to obliterate a quark soup is far beyond our abilities to test, but it can be calculated. At those energies things get even less intuitive. The forces themselves stop being the forces that you know. Electromagnetism and the weak force become the electro-weak force. Then at even higher energy levels, the strong force also merges, so at that point, even talking about quarks (and anything that's made from them) is meaningless. The forces and particles as you know them fundamentally change.

    The ability to melt protons into other things is not limited to neutron stars. The LHC creates all sorts of things from protons collisions including the Higgs boson.
  8. Jan 27, 2017 #7
    There is no such thing as "pure energy", just like there is no "pure velocity".
  9. Jan 27, 2017 #8
    I write "baryon burning" also to emphasize that the ~1MeV difference between proton and neutron is practically negligible there - it corresponds to barely ~10^10K, while neutron stars start with ~10^11K ( https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature ).
    My point is that if baryon number can be violated, it doesn't matter if it is neutron or proton what is decaying, even if they are smeared into a quark soup - baryon burning would mean, exactly oppositely to baryogenesis, that the total number of baryons is being reduced, and energy is increased by ~1GeV per each of them.
    Like in black hole transforming baryons into massless photons of Hawking radiation, but before forming the infinite density central singularity (Einstein's spacetime is "spiky" there: not differentiable, what means infinite density) - while crossing the threshold for baryon burning on this way to infinite density central singularity.

    So in the Universe I live in ... they have opposite charge and annihilate: as ortho-, or finally more likely: para-positronium: https://en.wikipedia.org/wiki/Positronium

    Could you elaborate on the possibility of calculating conditions required for e.g. proton decay?

    weirdoquy, by pure energy I have meant not imprisoned in the structure of a particle (its rest mass) - I have meant massless particles like photons (...gravitons?).
  10. Jan 27, 2017 #9
    My mistake about the positron.

    Please stop using the word decay. That's different. A Higgs boson decays. Some theories include proton decay, but the standard model does not. They're just melting.

    The energies your are talking about are usually talked about in cosmology: https://en.m.wikipedia.org/wiki/Electroweak_interaction. 1GeV is still low energy, the EM and weak force combine at about 100 times that. 100 times that the strong force also couples to this new force, and without the strong force, I'm not really sure what baryon numbers do.

    Hawking radiation has never actually been observed either. We know that the only thing that reaches those energy densities are black holes.

    Neutron stars are well understood and obey the laws of physics as the standard model predicts. They are well below the energy levels where the forces themselves break. They do not need to be held up by running anything, the quantum states get filled, that's what prevents it from collapsing. It's completely independent of heat, even an ultra cold neutron star will not collapse.
  11. Jan 28, 2017 #10
    If you want to ignore hypothetical Hawking radiation as example of violating the baryon number conservation, there still remains baryogenesis: how Big Ban has created more matter than anntimatter? Otherwise, we should e.g. observe 511keV halo from positron annihilation ...

    Ok, let's focus on examples I have already given in my first post above:
    Wikipedia article says "M82 X-2 is an ultraluminous X-ray source (ULX), shining about 100 times brighter than theory suggests something of its mass should be able to."
    Do you classify 100x divergence as "well understood"?
    Baryon burning could explain it (total matter -> energy conversion, coincidentally >100x energy density than from fusion) - what other energy sources could lead to such enormous luminosity?
  12. Jan 28, 2017 #11


    User Avatar
    2017 Award

    Staff: Mentor

    I've counted seven times, that you have used this term on this page alone which appears as a promotion rather than an accepted concept. Do you have any scientific (peer reviewed) references of what you mean by it, so we could debate it on a common basis? Or do you know of any newer papers than this outdated paper from 1993?


    I'm asking, for we do not want to discuss personal theories on PF.
  13. Jan 28, 2017 #12
    Proton decay, baryogenesis and Hawking radiation are all well known concepts considered for many decades - violating baryon number conservation.
    I have written "baryon burning" only as a mind shortcut, but if it is a problem I can use the complete phrase of what I have meant by that: "violation of baryon number conservation which releases energy of their rest mass".

    Exactly like in hypothetical Hawking radiation, but before forming the black hole - I am not claiming that it is possible, only ask about it.
    Also asking about energy source for ULX like M82 X-2: "shining about 100 times brighter than theory suggests something of its mass should be able to" - what are official hypotheses for such energy source?
  14. Jan 28, 2017 #13


    User Avatar
    2017 Award

    Staff: Mentor

    Then please find a reference that suggests this would happen more often at conditions found in neutron stars or at the LHC.

    Proton decay is typically assumed to be an effect of grand unifying theories, at 1016 GeV, way beyond the reach of neutron stars or accelerators. It can happen at lower temperatures, in the same way beta decays can happen at low energies - it is just unlikely, so we need big experiments with many nucleons. Adding a few MeV thermal energy doesn't change beta decays, and neither will it change proton decays.

    The event horizon forms before a stellar remnant is fully collapsed, see e.g. figure 1 here. Whatever happens in the late phases of the collapse does not matter - we don't see it.
  15. Jan 28, 2017 #14
    Ok, I accept that the answer to my question from the title is "no". Thank you.

    However, it means there is still a real problem with e.g. M82 X-2: "shining about 100 times brighter than theory suggests something of its mass should be able to" - so what are the official hypothetical explanations of such enormous energy source? (not violating baryon number conservation)
  16. Jan 28, 2017 #15


    User Avatar
    2017 Award

    Staff: Mentor

    There is nothing "official". Funneling of in-falling material along magnetic field lines as possible explanation is mentioned in the Wikipedia article.

    Note that an internal energy source is ruled out: no matter how it would look like, it could not lead to a luminosity above the Eddington limit. While we don't know how it is so bright, we know that it is not due to baryon decays inside.
  17. Jan 28, 2017 #16
    I will have to take a closer look at Eddington luminosity: from https://en.wikipedia.org/wiki/Eddington_luminosity
    "the maximum luminosity a body (such as a star) can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward."
    It seems that shifting the energy source to the falling material doesn't solve the problem: still being larger than Eddington luminosity should prevent further material from falling.

    There are a few ways mentioned in the article to go around the Eddington, for example using turbulences or extreme magnetic field - in this quickly rotating pulsar, far from being a spherically symmetric system.

    Do you have some stronger evidence to support your claim that internal energy source is already excluded - that it has to be an external one? (falling material)
  18. Jan 28, 2017 #17


    User Avatar
    2017 Award

    Staff: Mentor

    All those things are interesting, but they also work with all other power sources (including just a hot interior cooling rapidly). The question how it can appear so bright is independent of interior mechanisms of energy release.

    This is similar to stars: You have to know about fusion to understand how stars can live for billions of years. But you don't need it to explain how stars shine right now, other fusion cross sections or completely different energy sources would lead to very similar results.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Is proton decay considered in neutron star models (and LHC)?
  1. Neutron star (Replies: 9)

  2. Neutron Star (Replies: 14)