What is Neutron star: Definition and 173 Discussions

A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes, and some hypothetical objects (e.g. white holes, quark stars, and strange stars), neutron stars are the smallest and densest currently known class of stellar objects. Neutron stars have a radius on the order of 10 kilometres (6.2 mi) and a mass of about 1.4 solar masses. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.
Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star. Neutron stars are partially supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle, just as white dwarfs are supported against collapse by electron degeneracy pressure. However, neutron degeneracy pressure is not by itself sufficient to hold up an object beyond 0.7M☉ and repulsive nuclear forces play a larger role in supporting more massive neutron stars. If the remnant star has a mass exceeding the Tolman–Oppenheimer–Volkoff limit of around 2 solar masses, the combination of degeneracy pressure and nuclear forces is insufficient to support the neutron star and it continues collapsing to form a black hole. The most massive neutron star detected so far, PSR J0740+6620, is estimated to be 2.14 solar masses.
Neutron stars that can be observed are very hot and typically have a surface temperature of around 600000 K. They are so dense that a normal-sized matchbox containing neutron-star material would have a weight of approximately 3 billion tonnes, the same weight as a 0.5 cubic kilometre chunk of the Earth (a cube with edges of about 800 metres) from Earth's surface. Their magnetic fields are between 108 and 1015 (100 million to 1 quadrillion) times stronger than Earth's magnetic field. The gravitational field at the neutron star's surface is about 2×1011 (200 billion) times that of Earth's gravitational field.
As the star's core collapses, its rotation rate increases as a result of conservation of angular momentum, and newly formed neutron stars hence rotate at up to several hundred times per second. Some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars. Indeed, the discovery of pulsars by Jocelyn Bell Burnell and Antony Hewish in 1967 was the first observational suggestion that neutron stars exist. The radiation from pulsars is thought to be primarily emitted from regions near their magnetic poles. If the magnetic poles do not coincide with the rotational axis of the neutron star, the emission beam will sweep the sky, and when seen from a distance, if the observer is somewhere in the path of the beam, it will appear as pulses of radiation coming from a fixed point in space (the so-called "lighthouse effect"). The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c (i.e., nearly a quarter the speed of light).
There are thought to be around one billion neutron stars in the Milky Way, and at a minimum several hundred million, a figure obtained by estimating the number of stars that have undergone supernova explosions. However, most are old and cold and radiate very little; most neutron stars that have been detected occur only in certain situations in which they do radiate, such as if they are a pulsar or part of a binary system. Slow-rotating and non-accreting neutron stars are almost undetectable; however, since the Hubble Space Telescope detection of RX J185635−3754 in the 1990s, a few nearby neutron stars that appear to emit only thermal radiation have been detected. Soft gamma repeaters are conjectured to be a type of neutron star with very strong magnetic fields, known as magnetars, or alternatively, neutron stars with fossil disks around them.Neutron stars in binary systems can undergo accretion which typically makes the system bright in X-rays while the material falling onto the neutron star can form hotspots that rotate in and out of view in identified X-ray pulsar systems. Additionally, such accretion can "recycle" old pulsars and potentially cause them to gain mass and spin-up to very fast rotation rates, forming the so-called millisecond pulsars. These binary systems will continue to evolve, and eventually the companions can become compact objects such as white dwarfs or neutron stars themselves, though other possibilities include a complete destruction of the companion through ablation or merger. The merger of binary neutron stars may be the source of short-duration gamma-ray bursts and are likely strong sources of gravitational waves. In 2017, a direct detection (GW170817) of the gravitational waves from such an event was observed, and gravitational waves have also been indirectly observed in a system where two neutron stars orbit each other.

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  1. S

    I Can proton/neutron decay be avoided in some conditions?

    I was wondering whether the decay of neutrons and protons (if they happen to be able to decay, as it is predicted by some GUTs) could be avoided in some cases. Let's begin with neutrons: In principle neutrons have a very short time when they are isolated (around 10 minutes) and they suffer...
  2. RyanJ

    I Energy Released From Dropping Things Onto Neutron Stars

    Hi all. I'm trying to get my head back onto mathematical thinking and I'm setting myself projects to undertake to facilitate that. It's been too long since I've worked with numbers like this. My first task was to work out how much energy would be released when dropping things onto a neutron...
  3. C

    A Has the merger of a neutron star and an anti-neutron star been modeled?

    If a neutron star and an anti neutron star collided, would they 1) completely annihilate each other, 2) form a black hole, or 3) partially annihilate each other with the remaining stars being pushed away from each other by the energy created?
  4. PeterDonis

    I Physics Error in Larry Niven's "Neutron Star

    In the short story "Neutron Star" by Larry Niven, the narrator, Beowulf Shaeffer, is piloting a spaceship on a hyperbolic orbit that is supposed to make a close approach to a neutron star. He says at one point that he sees incoming light from distant stars blueshifted in all directions, and...
  5. C

    I Is it possible to unbind a neutron star?

    Type 1a supernovas unbind a white dwarf. Is there some theoretically possible scenario in which a neutron star could be unbound and thus turned into degenerate matter or even regular matter? For example, by a high speed glancing collision with another neutron star or by tidal disruption by a...
  6. K

    I Primordial neutron star -- a new candidate for dark matter

    could this explains the 3rd peak of the CMB and dark matter cold Primordial neutron star High Energy Physics - Phenomenology [Submitted on 7 Sep 2022 (v1), last revised 12 Sep 2022 (this version, v2)] Primordial neutron star; a new candidate of dark matter M. Yoshimura Z-boson exchange...
  7. D

    B What Could Explain the Mysterious Beam of Plasma Seen in the Sky in 2017?

    Basically, after seeing a meteor transit our atmosphere below 30,000 feet altitude too fast for my eyes to register yet leaving what looked like a beam of plasma from hanging from 1 side of the sky to the other for 3 seconds which I realized was a trail of smashed atoms of the atmosphere that...
  8. K

    B Object Weight on Magnetar vs Neutron Star: Attract or Repel?

    Probably a misguided question, but would the intense magnetic field of a magnetar increase the overall pull an object would feel at the surface of the magnetar as compared to a regular neutron star? Or would it possibly lessen the amount of gravitational pull the object would feel at the...
  9. B

    Statistical physics, using the ideas of Fermi Energies, etc. for a star

    a) V=(4/3)pi(r^3) N=M/m_n (M=mass of neutron star, m_n=mass of neutron) Subbed into E_f = (hbar^2 / 2m) (3(pi^2)N / V)^(2/3). T_F = E_F / k_B b) dU = (dU/dS)_s dS + (dU/dV)_s dV p = -(dU/dV)_s dV V=(4/3)pi(r^3) -> r = cubedroot(3V/4pi) subbed into U_g = -(3/5)(G M^2 / r) take (dU/dV) plug into...
  10. Grinkle

    B Maximum mass of a neutron star

    I read this - https://www.sciencedaily.com/releases/2018/01/180116093650.htm And I see this - "However, there are indications that a neutron star with a maximum mass would collapse to a black hole if even just a single neutron were added." And I think the maximum mass of a neutron star is...
  11. B

    B Collapse of a neutron star - strong nuclear force vs gravity

    I understand that gravity causes a neutron star larger than about 10 solar masses to collapse into a black hole. I also understand that gravity is the weakest of the four forces. So I find this counterintuitive and I'm puzzled that why is it gravity that causes the collapse and NOT the strong...
  12. Y

    I 9 y.o. question: will a spoon of neutron star matter explode?

    Greetings All, Well, this is the question from my 9 y.o. son: what will happen if a famous Everest heavy spoon of neutron star matter is actually removed from the star? I am inclining to his version that it will explode rather quickly, e.g. neutrons will quickly decay into protons-electrons...
  13. phinds

    I Discover the Rare Black Neutron Star

    This BBC article posts no references so I wonder if anyone has any idea how significant it is? https://www.bbc.com/news/science-environment-53151106
  14. T

    I What happens when a Neutron Star forms a Black Hole?

    Supposing the total mass of a stationary, non rotating Neutron Star is just one Kg below the mass required to form a black hole. Based on the wiki reference below the Schwarzschild radius must be just beneath the surface of the Neutron Star sphere. Now supposing an object with a mass of one Kg...
  15. T

    B What is the Cooling Time of a Neutron Star?

    Neutron stars have surface temperatures of 1,000,000 degrees K. Yet they are not creating energy like a normal star. They are just cooling off. How long does it take for such a star to cool to room temperature, 300 degrees K.?
  16. Attu

    B Neutron Star Paradox: Understanding Coulomb & Gravitational Forces

    For instance let's take that a neutron star mass is so high that the gravitational force is more than the coulumb force. If this happens then then the electrons will go down and alpha particle will be left . This is not observed in the star so how will the particle stay normal By the way I am...
  17. Moon Shine

    B Are supernovas more likely to produce neutron stars or black holes?

    I read that after explosions supernovas can ”transform” into a neutron start or into a black hole? And now I’m curious of therer any factors which can predict what thing we’re going to get after the supernova’s explosion.
  18. S

    I Neutron Star Core: Empty Obloid Cavity & Exotic Content?

    I have a question regarding Neutron Star cores that perhaps PF could clarify for me. Given a millisecond spinning NS, and given that its gravity decreases toward the center, being a spherical body, does centrifugal force displace the core material outwards to form an empty obloid-shaped cavity...
  19. K

    I Neutron Star Cores: Study Quantum Gravity Effects?

    Would neutron star cores be a good system to study quantum gravity? Core densities are higher than nuclear material. Is it possible cores exhibit QG effects?
  20. J

    B What would happen if we teleport 1mm^3 of neutron star core outside?

    Summary: hypothetical experiment, how would neutron core behave in such a circumstance such as, if we teleport 1mm^3 of neutron star core from it outside. how would the 1mm^3 neutrons behave? 1. Would it be stable/no change 2. Would it decay into cosmic radiation 3. would it decay into...
  21. AndrzejBania

    B What Size Would the Universe Be if Compressed to Neutron Star Density?

    Specifically, if you took all the regular matter that we believe to be in the universe and condensed it down to ‘neutron star’ levels of compression (Rather than ‘black hole’ levels)... How big a sphere would it make? I’ve always wondered, but never seen an answer posted anywhere Hopefully...
  22. P

    A Dark Matter Accretion Disk for Black Hole (Neutron Star)

    Hello! Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object. DM particles could be trapped and settled in around...
  23. P

    I Neutron vs electron degeneracy pressure

    How is neutron degeneracy pressure able to support a much higher density object such as a neutron star where electron degeneracy pressure only supports a comparatively less dense object such as a white dwarf. Conceptually I would think electron degeneracy pressure to be stronger due to the...
  24. P

    I Can a White Dwarf Collapse into a Neutron Star Without a Supernova?

    Is it possible for white dwarf star in binary system where it is feeding off its partner star to collapse directly into a neutron star? Or is something inherent in the formation of neutron stars where they must be formed from supernova?
  25. Grinkle

    B Observing a Beacon Impact a Neutron Star/Event Horizon

    If I am observing a pinging beacon free-falling into a neutron star from a distance far enough away that I am in approximately flat spacetime, I think I observe the pings redshifting as the beacon gets deeper into the gravity well, in other words I see the clock of the beacon slowing with...
  26. J

    I If we teleport 1mm^3 of a neutron star outside it what hapens?

    if we teleport a small amount of millimeter cube of a neutron star outside it, will it remain still as a very dense heavy neutron clump or will it revert back into its components (iron) or will the neutron destabilize and turn into cosmic radiation of neutrons which then turn back into hydrogen?
  27. T

    B Neutron Star Collisions: Creation of Heavy Elements and Their Fate

    When neutron stars collide, heavy elements, such as gold, are created. Are these elements ejected from the system to be found, say, here on earth? Or do they fall back into the newly created black hole?
  28. donielix

    I White dwarf collapses into a neutron star and Energy is released

    Hello everyone. I am trying to solve a problem whose statement reads as follows: Neutron stars have radii of ##\sim 10## km. If we assume that before the collapse the nucleus of the white dwarf precursor has a mass equal to that of Chandrasekhar, estimate the energy generated in the collapse...
  29. A

    B The Search for a Neutron Star or Black Hole Nearby

    If this is true where is the core of that star, either a neutron star or a black hole should exist near by, right?
  30. phyzguy

    A Neutron star collisions as a heavy element source

    There was a lot of discussion after the recent observation of the merger of two neutron stars about whether or not these events are the source of the heavier elements. See this thread, for example. This recent paper has some new analysis. Especially interesting is Figure 10, that I've...
  31. Arman777

    B MPEG movie: traveling to a black hole or a neutron star

    I find a very interesting site that shows us what it would be like to travel to a black hole or a neutron star. https://apod.nasa.gov/htmltest/rjn_bht.html Have fun !
  32. bbbl67

    I What is the minimum mass of a neutron star?

    We just discovered the maximum mass of a neutron star, discovered after the recent neutron star merger event back in Aug. They say that the maximum mass of a neutron star is approximately 2.16 solar masses. So I always assumed that the lowest mass for one is 1.4 solar masses, the Chandresekhar...
  33. wolram

    B Maximum weight of a Neutron star

    https://www.sciencedaily.com/releases/2018/01/180116093650.htm This article gives a maximum weight of 2.16 solar masses, and an infinitesimal addition would turn it into a Black hole. I can not find a paper to support this article so do you think it is correct?
  34. D

    B Gravastar vs. Neutron Stars: A New Theory for Black Hole Formation?

    Has anyone else heard of that gravity waves may be the result of another type of supernova remains, called a Grav-Star? It seems almost to physically mimic a neuron star but stopped just shy of becoming a black hole, yet it still has enough of a gravity well to prevent light from escaping. Is...
  35. Leonardo Machado

    I Why is neutron star interesting to physics ?

    I've seen many people who is studying it.. but why ? is there any contributions to physics at a foundamentalist level ? I mean, the properties of matter inside nêutron stars is the interesting part to theoretical physics and not the whole object right ?
  36. T

    I Low mass limit of a neutron star

    Note: this is QM question, not about stellar science. I am not asking what are the lightest neutron stars found in the Universe. The same star (say, 1 sun mass) can exist both in a form of a white dwarf and a neutron star. Both states are stable. However, let's say I start to stripe outermost...
  37. D

    I Understanding Neutron Star Formation Through Feynman Diagrams

    Hello, I recently watched a video as an introduction to Feynman diagrams for my own self-interest. The video gave a link to practice problems, and one of them was as follows: In a neutron star gravitational collapse causes valence electrons to combine with protons. Draw a Feynman diagram...
  38. S

    B Acceleration of a proton/electron toward a neutron star

    So, I have this scenario: A neutron star with radius R = 13 km Time for 1 rotation is 3,150807 ms, so frequency f about 317,379008 Herz Mass 1,97 times the Sun's which is then 1,97*(1,9884*10^30) kg Extra given information: the magnetic axis is aligned with its rotational axis (not that likely...
  39. W

    Does gravitational collapse limit Neutron Star size?

    Is there a theoretical limit to the size of neutron stars? It seems likely neutron stars are not simply electrons orbiting a proton so what is their life cycle? Can they just evaporate slowly by neutron decay?
  40. Borek

    I Neutron star merge why didn't all EM radiation came at once?

    Bear with me, I am just a chemist. Observations took several days (up to two weeks if memory serves me well). What I wonder is - why had different types of the EM radiation came at different times? Gamma burst was observed at almost exactly the same time gravitational waves were detected, but...
  41. M

    I Heavy elements from neutron star collisions?

    I have seen it claimed online that the recently announced observation of a neutron-star merger by LIGO provides strong support for the hypothesis that heavy elements - gold and platinum were mentioned in particular - are mostly created in neutron-star collisions rather than in supernovas. Is...
  42. B

    Safe distance from a neutron star

    what is the goldilocks range from a neutron star?
  43. K

    I Glueball with a mass of a neutron star

    new scientist July 15, 2017 current issue has article on boson stars, objects with the size and mass of stars, but composed of bosons. boson stars could mimic black holes. that got me thinking. if you had glueballs gravitational bound and the size and mass of a neutron star - or even larger -...
  44. S

    A Neutron star mass-radius relation plot

    Hi there... I have a question about the tipical mass-radius relation plot for a neutron star, something that looks like this for different equations of state: My question is, what is exactly happening at the ends of the EOS lines? I know that after passing the maximum mass the curve starts...
  45. C

    B Fast Radio Burst Pinned Down to Giant Stellar Nursery

    This appears to be a New Scientist scoop: Fast Radio Burst Pinned Down to Giant Stellar Nursery by Ken Croswell A young neutron star is probably the source of a repeating signal previously tracked to a dwarf galaxy 2.4 billion light-years away. Link: New Scientist
  46. W

    I Neutron Stars: Flipping Up Quarks to Down Quarks

    I am a casual follower of physics and was recently watching a YouTube video on Neutron stars. I am looking for a "simple" answer to this question. Per the video when the star collapses with the right mass to form a neutron star, at some point gravity forces electrons into protons and flips an...
  47. D

    Stargazing А neutron star and a photon sphere

    Wikipedia(https://en.m.wikipedia.org/wiki/Photon_sphere): 'This equation entails that photon spheres can only exist in the space surrounding an extremely compact object (a black hole or possibly a neutron star)' But how can a neutron star? I have a doubt because 1. When а mass of а star...
  48. J

    B Surface Temperatures - White Dwarf vs Neutron Star

    Hi, My textbook has a multiple choice question about which stellar object has the highest surface temperature and the answer was a white dwarf. However, one of the options was a neutron star. Neutron stars are much denser and have been crushed by gravity even more plus they are rotating at...
  49. J

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

    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...
  50. a1call

    B Neutron Star Becomes Black Hole: How Can 2 Realities Coexist?

    If a neutron star can be seen dense enough in some inertial frames of reference (due to relativistic length contraction) to form a Black-Hole, but not in others, how could the two realities coexist? Thank you in advance.