What is Neutron stars: Definition and 109 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. C

    Semi Empirical Mass Formula and Neutron Stars

    Sorry, the equations are messy. I already know the answer to the actual homework problem, but I don't really know why certain terms are neglected. I know that the equation will only include the volume term, symmetry term and the extra added gravity term. I just want to understand why I know...
  2. Astronuc

    B Vulpecula, pulsars and neutron stars

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  3. A

    B Mass transfer between neutron stars in a binary pair

    When we read about the mass transfer between neutron star pairs in a binary system, how is it that the one receiving the matter can increase its spin rate. Adding mass to a spinning object ought to slow due to conservation of momentum. Where does the energy come from?
  4. P

    B Interested in Black Holes, Neutron Stars, and White Dwarf Stars

    How did you find PF?: duckduckGo search. My math is very weak and I don't like explanations done using math. I read books with very little math. I try to use reason based on what I've read. My understanding is time slows down in gravity and it will actually stop at the event horizon (see...
  5. jedishrfu

    B There's Gold in Them Neutron Stars - or - Maybe Not

  6. Leonardo Muzzi

    I Why the center of black holes should be different from neutron stars?

    Physically speaking, why the insides of the least massive black hole should be any different from the heaviest possible neutron star?
  7. L

    B Colliding Neutron Stars Collapse into Black Holes

    Here is a presentation on the discovery of two colliding neutron stars and the resulting phenomena such as gravity waves, gamma ray bursts, and synthesis of high atomic number elements. The author is a theoretical physicist who is involved in the research. He says that the neutron stars most...
  8. D

    Semi-retired engineer, seeking knowledge of the greatest field in science

    I have a rudimentary understanding of classical physics and some (lesser) level of relativity and quantum mechanics. All came from undergrad studies before most of you were born. I tried to jump into the quantum world, only to find it necessary to relearn the basics of maxwells equations and...
  9. M

    B Can neutron stars lose energy?

    Since electromagnetic radiation is emitted as electrons decay from higher to lower states of excitation, I would assume that neutron stars cannot lose energy by blackbody radiation. That would leave tidal drag and evaporation as the only ways a neutron star can lose energy...True?
  10. Cerenkov

    B What are the maximum masses of White Dwarves and of Neutron stars?

    Hello. I'm very interested to find out more about the maximum masses of white dwarf stars and of neutron stars. Please note that while my level in this forum is Basic, I am familiar with the role that the Chandrasekhar limit has played in our understanding of white dwarves. I was therefore...
  11. Michaela SJ

    B Further collapse of Neutron Stars

    First post and I am not a scientist - just a curious soul. What stops a neutron star/magnetar from collapsing further into a black hole?
  12. Simon Peach

    B Why is the gravity of a neutron star stronger than that of its original star?

    I've just watched a vid about jets of matter and neutron stars. It was stated in it that a neutron star is a star that's been compressed from say a sun sized star to the size of a city, every thing OK upto now. Then it goes on to say that it has, the neutron star, enormous gravity, this is were...
  13. Spinnor

    B Galactic Collision Creates a Ring of Black Holes and Neutron Stars....

    From, https://www.syfy.com/syfywire/wham-bullseye-galactic-collision-creates-a-ring-of-black-holes-and-neutron-stars ..."“So you have a nice, normal spiral galaxy, right, just out there doing its thing, when BAM! A smaller galaxy careens right through the middle of it like a bullet! Chaos...
  14. Leonardo Machado

    I Neutron Stars mass and radii observation data

    Hello everyone. I'm currently working on NS mass relations and trying to plot a curve with predicted masses-radii and observations on NS. There are some free data at this website: http://xtreme.as.arizona.edu/NeutronStars/index.php/neutron-star-radii/ . I downloaded the .tar file and tried to...
  15. E

    I 2 second delay at the merger of two neutron stars in August 2017

    Some new papers appeared about processes in the collision of the two neutron stars, measured in August 2017. Is now more clear, why 2 second delay between gamma rays and gravitational waves happens?
  16. wolram

    B If Quark stars exist why do Neutron stars become Black holes?

    From Wikipedia: Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for...
  17. 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...
  18. G

    Why do neutron stars have such powerful magnetic fields?

    The sources I've looked at claim the magnetic field is present because there are still some electrons in the neutron star. Here is how I understand their reasoning: a star's radius significantly decreases when it collapses into a neutron star, ultimately decreasing its moment of inertia. In...
  19. J

    I Determining Mass & Info of Merging Neutron Stars from LIGO Signal

    How does one determine/calculate the masses, orbital period, and separation of two merging neutron stars from the characteristics of its gravity wave LIGO signal? And how does this information allow one to calculate the distance to the galaxy that housed the merger? And how can one calculate...
  20. A

    Question about the radiation around Neutron Stars or Pulsars

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  21. J

    B Black holes cause neutron fusion in neutron stars

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  22. Vanadium 50

    I Merging Neutron Stars: What We Know So Far

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  23. Ethan Singer

    I What causes pressure in White Dwarfs and Neutron Stars?

    Before today, I'd been led to believe that collections of only one (or few) types of matter could never exist: And to my surprise it is indeed possible to have degenerate matter, resulting from the death of less massive stars! So I'm curious: If these lesser massive stars collapse due to their...
  24. J

    B Are Black Holes Actually Giant Neutron Stars Cloaked in an Event Horizon?

    I was just wondering if there is anything to suggest that black holes are anything but giant neutron stars cloaked in an event horizon created by their own gravity. I mean if a neutron star is just on the cusp of having enough mass to be a black hole, and then gains that mass, what's to say it...
  25. N

    B Do neutron stars have a minimum volume?

    Do neutron stars have a minimum volume? Anything "in the way" of perhaps baseball sized neutron star? Or would something like that be an impossibility? How neat to have one in a laboratory...or not lol
  26. C

    How can neutron stars have magnetospheres?

    Neutron stars are neutral by definition. How can they have magnetospheres which are polar by definition?
  27. A

    B Mini Neutron Stars: What is the Smallest Possible?

    I know there is theoretical possibility of making mini black holes in particle acclerators, but what about mini neutron stars, or even mini quark stars? I realize the neutron decays in 15 mins if left all alone. What is the minimum number of neutrons needed inside a nuclei for it to be stable...
  28. L

    B Neutron Stars and Angular Momentum

    Some observed neutron stars rotate hundreds of times per second. Speeds at the surface of these stars are as much as 15% the speed of light. These huge speeds are generated because angular momentum is conserved when a large rotating pre-super nova star collapses into a neutron star. The...
  29. Irfan Nafi

    B What kind of supernova do binary neutron stars produce?

    I was wondering if a binary system of neutron stars were to collide what kind of nova or supernova would it be. Is it different if the final mass of the neutron star is sufficient enough for a black hole or if it still a neutron star?
  30. J

    B Do Atoms in Neutron Stars Touch Each Other?

    I have heard that in neutron stars, the atoms do not repel nor do they attract. In a sense, could this mean that these atoms nucleuses could touch each other, or could the atoms touch in general?
  31. J

    Initial Mass Function Question (white dwarfs, neutron stars and black holes)

    Homework Statement Calculate the number of white dwarf, neutron star and black holes the galaxy will have after 5Gyr of evolution. M<8(solar mass) for white dwarf 8(solar mass) < M < 40(solar mass) for neutron star M > 40(solar mass) for black hole Initial mass function is ξ(M) = AM-s...
  32. Elbert Anstein

    B Pulsars and Neutron Stars debunked?

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  33. R

    B How is the characteristic age of pulsars typically calculated?

    Hi everyone. I'm trying to derive the formula for the characteristic age of a pulsar. What I'm starting with is the following differential equation. dP/dt=K*P2-n What i think is odd, is several places they say solving this differential equation gives the following solution...
  34. B

    B "Gravitational Compression in Neutron Stars"

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  35. Jonathan Scott

    X-ray bursts might not happen for larger neutron stars?

    A method of definitely distinguishing a neutron star from a possible stellar black hole is that it produces X-ray bursts, which have a sharp rise time and may last for an extended period. I had previously thought these occurred when hydrogen fell to the surface and was immediately fused to...
  36. A

    Neutron Stars from White Dwarf Mergers: Under 1.4 SM?

    I think this could be a good chance that we see how neutron stars form from White Dwarf mergers. The combined mass of the two are less that than required for a type Ia Supernovae. Won't they merge and collapse into a neutron star? What does everyone else think might happen. I want to be sure if...
  37. Low-Q

    Can Neutrons Emit Light Without Electrons to Swoosh Them Away?

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  38. D

    Why don't all neutron stars collapse into black holes?

    If they are so insanely dense and their gravity is so mind-numbingly great, what prevents a neutron star from immediately collapsing into a black hole?
  39. Alex299792458

    Do neutron stars, pulsars, magnetars etc. have weather?

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  40. TheTuringTester

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  41. I

    Neutron stars and high density

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  42. D

    Creation of spinning neutron stars and pulsars

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  43. T

    About neutron decay in neutron stars

    Hi, I was reading about free neutron beta decay the other day and it came to me the idea of neutron stars. As I understand, neutron stars are held together by gravity instead of strong force interaction (which I think is the mechanism that gives stability to neutron in common nuclei). So one...
  44. Iulian Ionescu

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  45. skujesco2014

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  46. jlefevre76

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  47. A

    Why don't black holes look like neutron stars to outside observer?

    Yesterday, I read about Hawking's new proposal regarding the firewall paradox. A more general thought about standard black holes occurred to me. Black holes including stellar black holes are of course always presented as if the event horizon is an invisible barrier, which the unfortunate...
  48. I

    Neutron Stars vs Atoms: A Comparison

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  49. P

    Neutron stars on collision course.

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  50. R

    Neutron Stars: Quantum or Classical Objects?

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