Talk:Neutron star/Archive 2

Archive 1

Archive 2

Archive 3

Introduction

I think the introduction has too much unnecessary jargon in it. I think it should be simplified and made more clear.17:25, 26 October 2008 (UTC) —Preceding unsigned comment added by 75.150.72.237 (talk)

Formation

The information on gravity and escape velocity don't belong in this section and since it is already included in the properties section it is also redundant. It should be deleted from this section
Furthermore, I think there should be, if possible, more detail put into the formation.Alexa7890 (talk) 19:00, 26 October 2008 (UTC)

This section is really short. Perhaps it would be a good idea to include the end of a neutron star and change it from just a "formation" section to a "formation and end" section.Alexa7890 (talk) 07:04, 27 October 2008 (UTC)

Properties

Is the information on the Equation of State correct? The citation that is given (#3) goes to the German page on neutron stars. I have come across articles that discuss the EoS for Neutron Stars which would imply that an EoS is known. Alexa7890 (talk) 13:16, 27 October 2008 (UTC)

No, the EOS is not known with ANY certainty. There are infact many competing modals. You should be cautious with neutron stars - they tend to publish "facts" about them decades before an issue is settled, or even properly explored. —Preceding unsigned comment added by 75.153.125.20 (talk) 01:42, 13 December 2008 (UTC)

The crust would appear black because all radiation is focused around the X-ray spectrum. Is this correct? Just because the radiation peaks in the X-ray doesnt mean it wint be radiating in the visible. Wont it look purple like other things that peak above the visible? Fig (talk) 12:37, 17 November 2008 (UTC)

Yes, that's wrong. When ideal black body is heated, maximum moves to shorter wavelengths, but partial luminosity grows in all spectral channel, there is no channels where it falls! IIRC, long wavelengt parts of spectrum (those far from peak) rise approx. proportionally T. As a result, bolometric luminosity rises proportionally to T^4.

Thus, neutron star is (unimaginably intense) white in visible light, because peak is so far away in X-rays, all colors of visible spectrum will have approximately same intensity. Hence, white. —Preceding unsigned comment added by 88.101.163.106 (talk) 01:10, 10 December 2008 (UTC)

The escape velocity is listed as 30% of speed of light and as 50% the speed of light, if it does vary that much it needs to be mentioned, as it is now it conflicts with the previous paragraph —Preceding unsigned comment added by Edman007 (talk • contribs) 16:59, 17 November 2008 (UTC)

Structure

The information of the density seems to belong in the properties section. The second paragraph needs to be considerably cleaned up. The "proceeding deeper" vocabulary isn't something that would be in an encyclopedia and the information should be made more clear. —Preceding unsigned comment added by Alexa7890 (talk • contribs) 23:14, 22 October 2008 (UTC)

Depth of The Crust

The crust is 1 meter or 1 mile thick? (section on structure). The text and the figure are contradicting themselves. 201.80.110.49 (talk) 05:31, 30 November 2007 (UTC)

The thing that is being referred to as 1 meter thick is the atmosphere, however from what I know this is incorrect. According to The Internet Encyclopedia of Science what can be called an atmosphere is maybe only a few micrometers thick. The figure is correct according to Universe Today and Space.com Alexa7890 (talk) 15:13, 22 October 2008 (UTC)

• Neither 1 meter nor a few micrometers are quite correct for the atmosphere: a typical depth scale in the neutron-star atmosphere is from a few millimeters to a few centimeters, depending on conditions (chemical composition, temperature, stellar mass and radius, magnetic field). 1 meter can be correct for the heat-blanketing envelope. For the entire crust (including the inner crust), the order of magnitude of 1 km is correct for typical neutron stars. Potekhin (talk) 08:12, 30 January 2009 (UTC)

Annd this was verified to be accurate by what means? —Preceding unsigned comment added by Trentc (talk • contribs) 03:24, 5 March 2009 (UTC)

Radius, volume, density in curved space

All the calculations regarding the volume and density of a neutron star that I have seen assume that the space inside a neutron star is flat. However, inside an object as massive as a neutron star, doesn't the curvature of space become significant? Wouldn't that mean that the internal volume is larger than the standard formula for a Euclidean sphere would suggest? I hope someone more familiar with General Relativity can answer these questions. Clement Cherlin 01:16, 16 November 2007 (UTC)

• All serious calculations of this kind are always done in frames of General Relativity. The flat spacetime may be considered as a simplification for general reader, because in many cases this approximation gives a correct order of magnitude for neutron stars. Potekhin (talk) 08:15, 30 January 2009 (UTC)

Magnetars categorised as rotation-powered neutron stars

Isn't a magnetar's power source it's magnetic field energy?

See http://solomon.as.utexas.edu/~duncan/magnetar.html#New_Kind_Of_Star

there is alot of argument over this. It seems like it is it's magnetic field - but the origin of the field itself is open to discussion. It's like saying your TV is electric powered - ignoreing the coal plant on the other end. Also, most neutron stars are rotation powered - the high field stars seem to be an exception, but we really don't know with any certainty. —Preceding unsigned comment added by 75.153.125.20 (talk) 01:44, 13 December 2008 (UTC)

89.48.108.46 (talk) 16:22, 11 December 2007 (UTC)

• This issue is not definitely solved yet. Most popular hypothesis is that the source is the magnetic field energy, but there are alternative models. Potekhin (talk) 08:17, 30 January 2009 (UTC)

SOLAR MASS

SOME ISSUES HERE WITH THE SOLAR MASS OF THE NEUTRON STAR AND THE SUN. IF IT IS 1.35 SOLAR MASSES, THEN IT WOULD NOT BE SMALLER THAN THE SUN —Preceding unsigned comment added by 155.214.128.4 (talk) 15:38, 26 February 2008 (UTC)

Yes, it can be smaller, if it is denser. And neutron star are very dense. --84.10.180.181 (talk) 14:36, 23 March 2008 (UTC)

Surface gravity

The value of 2×10¹² g is far too high. If approximated by Newton's Law of gravity a 2 solar mass neutron star with 10 km radius would have about 2.7×10¹² m/s² = 2.7×10¹¹ g. A 3 solar mass black hole would have about 5×10¹¹ g (at the Schwarzschild radius of 9 km}}. Although one would have to use the relativistic equations for a correct result the Newtonion equation should at least give the correct order of magnitude. I have therefore corrected the value in the properties section; the range of 2×10¹¹ to 2×10¹² g given a few lines above remains as a matter of further check (with relativistic formulae, if possible).--SiriusB (talk) 15:02, 26 December 2008 (UTC)

• Yes, relativistic formulae give corrections of a few tens percent at most, so the order of magnitude is the same as with the Newton's Law of gravity. For typical neutron stars the surface gravity is a few ×10¹⁴ cm/s² = a few ×10¹² m/s². And you are right, the range of 2×10¹¹ to 2×10¹² g given a few lines above is incorrect as well. According to the family of the equations of state presently considered in the literature, it is possible for a neutron star to have the surface gravity from 0 (for the minimum-mass neutron star) to about 7×10¹⁴ cm/s² (see, e.g., Bejger, M.; Haensel, P. (2004). Surface gravity of neutron stars and strange stars. Astronomy and Astrophysics 420, 987-991). However, most typical neutron stars with masses of 1 to 2 solar masses should have surface gravity somewhat between 1×10¹⁴ cm/s² and 5×10¹⁴ cm/s². I have therefore corrected that point in the "Formation" section. Potekhin (talk) 18:24, 29 January 2009 (UTC)

What happens to them eventually?

How does a neutron star end it's life, what happens to it? And how? It doesn't have fuel like a regular star, and it's gravity holds it together, how long can they stay that way? The snare (talk) 05:51, 19 August 2008 (UTC)

You don't know much about gravity do you? Gravity is the reason its smaller then earth... Gravity is crushing it. Thats why it has such high pressure. Ulitmatly it would porably either be crushed or the nuetrons would escape.--Jakezing (talk) 13:19, 27 October 2008 (UTC)

Jakezing, I asked my astronomy professor about this and she said that a neutron star will remain mostly static, although they will cool down a bit Alexa7890 (talk) 02:26, 28 October 2008 (UTC)

He may be a professor but that dosn't make him right.--Jakezing (talk) 22:20, 28 October 2008 (UTC)

Who is youtr daddy and what does he do? Who are you and what are your credentials?. Reeks of pungent arrogance. -220.255.7.249 (talk) 11:27, 24 December 2008 (UTC)

A neutron star will end it's life quietly - the professor is correct. At least for most stars. And yes, that doesn't make him necessarily correct, but noone is ever necessarily correct. Vacuous statement. —Preceding unsigned comment added by 75.153.125.20 (talk) 01:45, 13 December 2008 (UTC)

I'm still a little confused, so it will cool down, but then what? Break apart and dissipate somehow? And how will it do that? The snare (talk) 03:20, 24 January 2009 (UTC)

Why do you think something else must happen? Assuming the neutron star is isolated and no external matter is falling in, it would be pretty safe to say that nothing will happen. Now, it's possible that after an extremely long amount of time (something like a trillion trillion trillion times the age of the universe) pending confirmation that baryonic matter can decay into non-baryonic matter (never been observed), the neutrons might decay into lighter particles (mesons and leptons) and eventually the star would evaporate. That scenario must be considered speculative. Dauto (talk) 05:12, 29 January 2009 (UTC)

So, you're saying neutron stars are eternal as far as we know? When there is nothing but photons left in the universe, there will also be neutron stars literally forever? Also, don't neutrons become protons, at least when they are alone and not in a nucleus? The snare (talk) 02:22, 2 February 2009 (UTC)

That's right. Neutrons left alone become protons in 15 minutes, but neutrons in a neutron star are stable. Unless all baryonic matter converts in nonbaryonic matter (hypothetical possibility as mentioned by Dauto), an isolated neutron star will be eternal. But if a neutron star accretes matter, it may eventually collapse into a black hole. Potekhin (talk) 05:28, 2 February 2009 (UTC)

Don't atoms (normal ones, so a deuterium atom in this example- just so we have one neutron) eventually break down and dissipate? They don't last forever, so I've been told, they aren't perpetual motion machines, don't know about neutron stars though. The snare (talk) 03:14, 16 April 2009 (UTC)

Deuterium is stable, and does indeed last forever. Tritium is the unstable isotope of hydrogen. It beta-decays, transforming one of its neutrons into a proton, and continues as helium-3, which lasts forever. Matter changes forms, but doesn't generally disappear (barring exotic processes like proton decay, which hasn't been observed). The key concept is that the amount of mass (or energy) involved remains constant. --Christopher Thomas (talk) 21:52, 27 May 2009 (UTC)

Don't forget about the gravity of the thing. It's really strong and makes it hard for matter to escape, so the example with deuterium doesn't really apply here. And yes, neutron star isn't a perpetual motion machine, it emits a lot of energy during it's lifetime - that's why it cools down. Regarding the topic, it's really hard to say how does the star end it's life because we can't see the really old ones - they're too cool and therefore emit too little energy to be observed. In theory they can live forever or collapse into a black hole as said by Potekhin or maybe they change into a basket full of oranges ;), we will probably never be sure of that. --Siberie (talk) 04:55, 24 May 2009 (UTC)

Question

How is it possible for a neutron star to be very hot. Atoms and molecules are to be in motion for the flow of charge of heat while there is no charge on neutron star. Myktk (talk) 15:36, 21 October 2008 (UTC) Khattak

I think it has to do with compressing the core of a star into something smaller then earth and having all of it be neutrons, Pressure and heat go hand in hand and neutron stars are like black holes just less gravity..--Jakezing (talk) 13:18, 27 October 2008 (UTC)

heat and charge are two very different things, temperature is the average speed its molecules/particles are moving at, see Heat and Temperature, charge is in basically from charged particles (protons/electrons) see Electric_charge, with a lot of the high temperature things the heat can separate the electrons from the nucleus, leaving many charges particles (ions) which allow the plasma to become "charged" which is what your thinking of see Plasma_(physics), with a neutron star the pressures become so great that the electrons combine with the protons (a + and - charge equals a 0 charge), and if you have no charged particles you have no charge as a whole (see Degenerate_matter#Neutron_degeneracy) Edman007 (talk) 06:01, 24 November 2008 (UTC)

The above poster claiming that charge and heat are different is correct. But to answer your question more fully - Temperature is related to the ratio of a change in entropy to a change in energy. A very small change in entropy here requires a massive change in energy, because the star has such high density. The result is that the temperature is very high. To the poster who claimed that neutron stars are like black holes - thats really not a fair comparison. Black holes violate in principle every law of physics. People like Hawking, Wheeler, and Unruh have spent their lives figureing out how our laws of thermodynamics can exist next to black holes - forget working INSIDE them! —Preceding unsigned comment added by 75.153.125.20 (talk) 01:49, 13 December 2008 (UTC)

It's not clear to me what the original poster meant with that question. He mentions the fact that neutrons are not charged particles but does not explain why he thinks that the presence of charged particles should be required in order for something to be very hot. He might want to better explain his position. He seems to believe that only charged particles can have a temperature. That's simply not true. Dauto (talk) 05:21, 29 January 2009 (UTC)

I've wondered this too. Heat is determined by how fast the electrons are moving, but since a neutron star is all neutrons and no electrons, how can it have heat? The snare (talk) 03:10, 16 April 2009 (UTC)

Heat is determined by the energy of the moving particles. Boltzmann's constant says that on average a particle will have 1.38×10⁻²³ Joules/Kelvin . This is true for electrons in most metals because they act as a gas. It is true for molecules in a gas and nuclei and electrons in a plasma. Neutrons will jostle around in a neutron star just like molecules in a gas. At 1×10⁶ K , their mean velocity will be about 128 km/s which is ~c/2000. They are likely superconductors of both heat and electricity. The later may explain the huge magnetic fields in neutron stars. Trojancowboy (talk) 02:37, 28 May 2009 (UTC)

"The nuclei become smaller and smaller until

the core is reached, by definition the point where they disappear altogether." (a quote from current article) I wonder about the accuracy or at least the clarity. The sentence seems to be saying that a "neutron star" must "by definition" have at least some location where matter exists only as neutrons(and thus must at least have it in the core), but I doubt astronomers think that way. Astronomers probably identified some objects that they suspected had that property, and called them neutron stars, but they're not defined by that, but probably by observational characteristics, whether or not astronomers now know if some or all neutron stars have matter of this form.Astronomers don't define their universe, they (try to) describe it.--Richard Peterson75.45.97.146 (talk) 18:10, 7 May 2009 (UTC)Rich (talk) 21:12, 7 May 2009 (UTC)

Neutron stars are defined as bodies supported by neutron-degeneracy pressure (though the term as used by astronomers will also cover things like quark stars and other stars with exotic hadrons). Whether the nuclei grow smaller as you move deeper within the star is debatable, as that depends on the equations of state for nuclear matter, which are poorly understood. What people will agree on is that near the surface, you'll have ordinary nuclei and a degenerate gas of electrons. Deeper in, it becomes energetically favourable to convert electrons and protons into neutrons, so you end up with nuclei past the neutron drip line that are stabilized by external fluid pressure. A bit deeper, and it's energetically favourable for some of these neutrons to un-bind from nuclei and be shared as a degenerate gas of neutrons (like the Fermi gas of electrons in a metal). This may happen piecemiel, with smaller nuclei within the gas (either as a solid or moving as a fluid), or it may happen all at once, with a sharp transition between matter composed of nuclei and a neutron-degenerate fluid (someone's probably figured out which of these happens, but you'll have to dig up relevant papers to find out which occurs). Either way, past a certain depth, you have neutron-degenerate matter without distinct nuclei. I'm told this ends up acting like a superfluid (behavior is dominated by quantum effects rather than classical). Even farther in, the neutron-degenerate matter may or may not convert to other forms of matter (quark soup or strange matter). Whether or not it does this depends on the equations of state of all of these forms of matter (it'll happen if and only if it's energetically favourable to do so at the pressures and temperatures found within the star). --Christopher Thomas (talk) 20:18, 7 May 2009 (UTC)

you obviously know a lot more than me about it, and what you said seems to partially support my point, so let's fix the sentence in question.75.45.97.146 (talk) 21:03, 7 May 2009 (UTC)Rich (talk) 21:12, 7 May 2009 (UTC)

I just changed it to something I think is a better approximation to current understanding, but you probably should write it the way you think best.Rich (talk) 21:12, 7 May 2009 (UTC)

More Questions

"Outside the nucleus, free neutrons are unstable and have a mean lifetime of 885.7±0.8 s (about 15 minutes), decaying by emission of a negative electron and antineutrino to become a proton:[6]" Source: http://en.wikipedia.org/wiki/Neutron So its life time should not be more than 15 second.

Also, if surface gravity of neutron star increases 7x10^14 every meter in one second then is this figure higher than speed of light? 96.52.178.55 (talk) 17:00, 31 May 2009 (UTC)Khattak

I think you mean "15 minutes", not "15 seconds". The key concept here is that particles are stable when decaying would cost them energy, and are unstable when decaying would produce extra energy. In vacuum, or in an environment like Earth's, neutrons are unstable, because a proton plus an electron has lower energy (rest mass plus minimum kinetic energy) than the original neutron. Within the neutron star, however, matter is packed very densely (dense enough to be degenerate matter). In degenerate matter, all particles have to occupy different energy levels (they aren't allowed to have the same energy, angular momentum, and quantum spin as another particle). The energy levels allowed for electrons under these conditions are much higher than the energy levels allowed for neutrons, so neutrons decaying (into proton-plus-electron pairs) would require extra energy. The neutron is the lower-energy state under these conditions, so inside a neutron star, neutrons are stable.

With regards to surface gravity, the important thing to realize is that gravitational acceleration and escape velocity are very different things. Gravitational acceleration tells you how fast you're picking up speed when falling towards an object, and escape velocity tells you how fast you have to leave the surface in order to escape the object. When you're right near the surface of a neutron star, it'll pull you towards it very quickly. However, the neutron star is small compared to other celestial bodies, so the distance over which you speed up this quickly is relatively small. As a result, the speed needed to escape is still less than the speed of light.

I hope this answers your questions. --Christopher Thomas (talk) 07:37, 1 June 2009 (UTC)

Yes, I meant 15 minutes. Thanks.96.52.178.55 (talk) 04:29, 3 June 2009 (UTC) khattak

Stability

Neutron stars are very hot and are supported against further collapse because of the Pauli exclusion principle. - This statement is not entirely correct. Of course the exclusion principle is important here, but it's too weak to support the star. The major contribution to force that counters gravity are repulsive nuclear forces which come into the game because of huge density. I think it should be corrected. Any comments? Siberie (talk) 14:57, 25 May 2009 (UTC)

The "repulsive nuclear force" you refer to is degeneracy pressure. As density increases, confinement requires energy to increase as well. Net result is a repulsive force. See degenerate matter for the derivation. The Strong force is purely attractive, and the Weak force is mostly mediating the transformation between neutrons and electron-proton pairs.--Christopher Thomas (talk) 21:42, 27 May 2009 (UTC)

Yup, You're obviously right. I had to be really tired to write such a BS. Thanks for correcting it. Siberie (talk) 13:31, 30 May 2009 (UTC)

Enormous Magnetic Fields

This subject is not even discussed and needs to be a prominent part of the article. Magnetic fields of 10×10⁸ Tesla are common or 100 million times greater than a rare earth magnet This is one of the MAIN properties of a neutron star. Magnetic poles are usually not aligned with the axis of rotation which gives a pulsar.Trojancowboy (talk) 03:02, 28 May 2009 (UTC)

Actually it is mentioned 8 times. But I too think it deserves a section to itself. I'll get out my college textbook and look it up. Marx01 ^{Tell me about it} 00:20, 28 September 2009 (UTC)

Where is the closest neutron star?

I found some lists of known neutron star on Gooogle but some without distances. I'm wondering how far away the closest is. —Preceding unsigned comment added by 71.186.61.183 (talk) 13:10, 14 July 2009 (UTC)

You can find a list of a few neutron stars at Category:Neutron_stars. These should include position and distance information. You can also try entering the name of a neutron star you find on Google into Wikipedia or into Google again, to get location information (right ascension, declination, and distance). Typical values seem to be 500-600 light-years for the ones we know about.

There might also be selection bias involved. We'll have found neutron stars that are observable as pulsars, but these are only the ones that are a) still strong radio emitters and b) aligned so that their radio beams cross Earth. We'll have found neutron stars that are observable as x-ray sources, but these are only the ones that are either newly-formed or consuming matter from a companion. We'll have found those that are young, by looking for radio and x-ray emissions near supernova remnants, but older neutron stars could easily have moved away from the remnants (asymmetries in the supernova explosion can kick the neutron star out at considerable speeds). So, there will be many neutron stars that we can't detect, either because they're pulsars that don't sweep across Earth, or because they're old and far from their birthplaces, or both.

I hope this helps answer your question! --Christopher Thomas (talk) 06:14, 15 July 2009 (UTC)

Conversion of protons and electrons to neutrons

I came to this article looking to find out how a conventional star made up of atoms (protons/neutrons/electrons) ends up with the protons and electrons gone and the neutrons remaining. Any chance there's a guru out there that can explain it? After all, that's sort of the whole neutron star formation thing. Grumpyoldgeek (talk) 21:00, 11 June 2009 (UTC)

This is covered to some extent in a thread a bit farther down this page. The short version is, the Weak Nuclear Force allows a proton and an electron to convert to a neutron (plus an electron neutrino), and also allows a neutron to convert to a proton and an electron (plus an electron antineutrino). The most common place where this process occurs is beta decay of neutron-rich elements. The reaction can go in either direction. Which direction it goes in depends on whether "proton plus electron" or "neutron" is the lower-energy state. Under normal conditions, "proton plus electron" has lower energy, so free neutrons are unstable and normal matter doesn't spontaneously transform into neutrons. Within the neutron star, though, the star's mass is confined into a small enough volume that keeping most of that matter as neutrons is the lower-enregy state (detailed reason is that electrons, being light, have longer wavelengths for a given energy, so confining that many of them to a volume as small as a neutron star requires giving them extremely high energies, compared to the energies you'd need to give neutrons to confine them in that volume).

I hope this helps! --Christopher Thomas (talk) 02:51, 12 June 2009 (UTC)

Nicely said, thank you.Grumpyoldgeek (talk) 17:38, 12 June 2009 (UTC)

The concept of the atom can be boiled down to it's being an almost in contact accumulation of deuteron pairs plus extra neutrons and surrounded by a cloud of electrons. And a Neutron star concept further whittles the size down such that the space for the cloud of electrons is eliminated. And the presumption of neutral atomic charge pretty much assumes that each electron must return to it's associated proton. So everything is neutral. And the concept of the continued existence of individual nucleons requires a packing system similar to what exists in the nucleus of the normal atom, which is pretty closely packed. But it's hard on the accumulated repulsive force theory and might require some rethinking about that. And it makes you wonder about the quark electrostatic charge existence and change mechanism logic, but we wouldn't want to do that.WFPM (talk) 19:07, 4 May 2010 (UTC)

Schwarzschild radius

How does this article relate to the Schwarzschild radius? http://en.wikipedia.org/wiki/Schwarzschild_radius Should there be a connection of ideas between these two ideas?

Reddwarf2956 (talk) 19:40, 31 August 2009 (UTC)

I would think so since a neutron star has quite a bit of mass to it, crushed into little more than ten kilometers. However I calculated an estimate for the radius of a 10 km neutron star with a density of 10¹⁴ and ended up with 5.2x10^-41, and I'm not sure if I screwed up somewhere or that is the actual value, but if you can I would put the numbers into consideration before writing it. Thanks for bringing that up! Marx01 ^{Tell me about it} 01:39, 17 September 2009 (UTC)

There isn't much of a relation between the articles. Mostly, a neutron star represents the most compact possible object that does _not_ collapse into a black hole (no other known forms of degeneracy kick in past neutron degeneracy, with the possible exception of quark degeneracy as mentioned in the article). Neutron stars have a mass of about 1.5-3 times that of the sun, giving equivalent Schwarzschild radii of about 4.5-9 km. --Christopher Thomas (talk) 02:11, 17 September 2009 (UTC)

How close

How close (what range of distance) to a neutron star does pair production happen? It is know that near heavy dense atoms in which a two times electron rest mass energy gamma ray comes close pair production happens. How much mass is gained/loss by this production?

Reddwarf2956 (talk) 19:52, 31 August 2009 (UTC)

Pair production could happen when a sufficiently energetic photon passes near any of the nuclei in the star's crust. There are probably interactions with free neutrons within the star that could do it to, but you might need more than one neutron to get all of the quantum numbers shuffled to the right places (not sure). "Near" in this context means within a few wavelengths of the gamma ray, if I understand correctly, so as far as the gamma ray is concerned it doesn't matter if the nuclei it's interacting with are part of a star or not. To the best of my knowledge, you aren't going to get interactions that affect the star as a whole (with the possible exception of degeneracy tweaking the threshold energy within the star's core, due to constraints on how the energy and momenta of individual particles can change).

Pair production converts some or all of the gamma ray's kinetic energy into the rest energy of the pair of particles produced. Some additional kinetic energy and momentum can get shuffled between the nucleus, the gamma ray, and the particles produced, but the gamma ray is the only thing that loses energy. --Christopher Thomas (talk) 02:08, 17 September 2009 (UTC)

German wikipedia as Reference

The sixth source in this article is said to be the germans wikipedia. i dont think that is right. could someone mark that as unverified and get someone to get a verifiable source for that information 66.90.164.132 (talk) 18:55, 5 November 2009 (UTC)HTU-Student

 Done with this edit, summary: "replace one german wikipedia reference with cite of Corvin Zahn, remove others; need relativity expert to check my hopefully correct treatment of natural units" -84user (talk) 16:17, 22 December 2009 (UTC)

Invalid Density Reference

At the end of the second paragraph, the article states, "This density is approximately equivalent to the mass of the entire human population compressed to the size of a sugar cube."

With over 7 million humans currently inhabiting the Earth, within the parameters of errors, deaths, and unrecorded populations (tribes disconnected from the outside world), this is not a valid argument. Likewise, without a statistical date, one could describe the density of a neutron star as being similar to that of the human population of the plague-ridden medieval age. For something so immensely dense as a neutron star, it likely doesn't matter much the mass of humans it would take to approximate the density of a neutron star. It's a simple fact that the original statement is too vague to be a valid statement.
Christopher, Salem, OR (talk) 12:53, 18 May 2010 (UTC)

Since my last posting on the discussion of this article, I have taken note of the addition of the reference as I requested. Though I am unfamiliar with Ankit Srivastava page (http://www.ankitsrivastava.net/2010/06/neutron-stars-sugar-cubes-and-squeezed-humans/), I feel that this reference goes above and beyond at clarifying the statement, "This density is approximately equivalent to the mass of the entire human population compressed to the size of a sugar cube."

Well done. Now there's some numbers to wrap 'round our brains.
Christopher, Salem, OR (talk) 10:51, 18 June 2010 (UTC)

Small Fact about Neutrons

This is my first time on a talk page, so please forgive and correct me if I do anything wrong.

There is a small fact in the top paragraph stating that neutrons have roughly the same mass as protons. Would it be acceptable for me to change that to "a slightly larger mass than protons"?

I decided to go with the "be bold" principle. And for anyone who is worried, I will watch my spelling in actual article edits.

KKPie (talk) 15:36, 18 June 2010 (UTC)

Pressure at/after/near collapse

Could the article mention that the core degeneracy pressure at collapse approaches the maximum possible theoretical pressure of P = pc² , where p is the density? 172.129.30.241 (talk) 01:19, 18 August 2010 (UTC) BG

1. Can the article give an approximate range for estimated core pressures in a neutron star? For starters wouldn’t the non-relativistic core pressure of a neutron star be given approximately by P(c) = KGM²/(πR⁴), where K is a constant dependant on the density profile, but nominally equal to 1. For 1.35 to 2.1 solar mass stars, this would give estimated pressures of about 1 X 10³⁴ to 2 X 10³⁴ kg/m². The magnitude of this approximate pressure is mind boggling. It would be equivalent to about the entire weight of the sun pressing down on 1 cm² at the earth’s surface. This is a sloppy calculation and maybe others could improve it. It would be nice if someone could give a better equation for core pressure or at least the results. Does someone have Tolman–Oppenheimer–Volkoff equation solutions for a neutron star? I don't accept the TOV equation but many others do.

2. To diverge, why should collapse of this type structure lead to a point singularity? If during collapse the mass not blown away is large enough to form a black hole, shouldn’t the resulting high temperature essentially convert all this mass into contained radiation? The basic pressure formula for this intense radiation would likely be P = pc² (where p is the equivalent mass density of the energy). This should prevent collapse to a singularity since this pressure has no limit and increases as 1/R³, faster than the increase of gravitational force. 172.162.242.8 (talk) 19:59, 23 September 2010 (UTC)BG

As was explained to you at talk:black hole, relativity can't be neglected when doing this calculation, as its effects dominate. That is why the Chandrasekhar and TOV limits occur.

Also as was explaiend to you at talk:black hole, Wikipedia really isn't the place to ask about this. I suggest asking on one of the physics newsgroups. --Christopher Thomas (talk) 22:56, 25 September 2010 (UTC)

Good idea. Your comments are welcome at http://www.physicsforums.com/showthread.php?p=2905538#post2905538 ````BG —Preceding unsigned comment added by 172.129.106.208 (talk) 00:29, 29 September 2010 (UTC)

Maybe you directed me to the forums as punishment. Perhaps some there believe a BH is made of chocolate pudding. Now I long for the days when conversations were dominated by singularity advocates. 172.163.115.55 (talk) 18:37, 29 September 2010 (UTC)BG

I directed you there because detailed discussion is on-topic/appropriate there, unlike here. No more, no less. There were several other venues mentioned in the banner at Talk:Black hole; by all means try some of the others if the forum is not to your taste. --Christopher Thomas (talk) 18:56, 29 September 2010 (UTC)

Yes. Radiation pressure of pc^2 or (pc^2)/3 shows why collapse should not occur in the core of a black hole. But it does not explain why collapse should not occur at the black hole surface. But based on E = mc^2, the absolute maximum pressure P that matter should be able to support is P = pc^2, where p is the density of the matter. Its interesting that neutron star cores at collapse approach this pressure.172.162.222.11 (talk) 13:18, 5 October 2010 (UTC)BG

It would be interesting to know if neutron star core collapse occurs at a pressure of (pc²)/3, at pc², or somewhere in between. Does anybody have this information or an estimate? Possibly it could be added to the article. 172.130.75.73 (talk) 19:42, 17 October 2010 (UTC)BG

Copyrighted section removed

I was bold and removed the Disrupted Recycled Pulsar section as it was copyrighted. The origin of this section was from this link http://www.scientificcomputing.com/news-DS-Einstein-at-Home-Citizen-Scientists-Discover-New-Pulsar-081210.aspx

Notice at the bottom of the article "Science Express, August 12, 2010". This section was added on August 31, 2010 as shown in this link: http://en.wikipedia.org/w/index.php?title=Neutron_star&oldid=382083718

Obviously a copyright violation. Good information if worded differently but until that is done, we can't have it on Wikipedia. —Preceding unsigned comment added by 97.112.196.161 (talk) 00:01, 1 September 2010 (UTC)

Question about rotation and life span

How come the slow down rate/ rotation occur after a century or million years when we all know that free neutrons undergo beta decay with a half-life of about 10 minutes and are not readily found in nature, except in cosmic rays.68.147.41.231 (talk) 04:55, 7 November 2010 (UTC)khattak#1

Neutrons within neutron stars are stable. A neutron star is compact enough that an equivalent number of electrons within it would have to have extremely high energies, due to being a degenerate gas. This makes it energetically unfavourable for neutrons to decay (the resulting proton plus electron would have more energy than the original neutron), so they don't. --Christopher Thomas (talk) 08:25, 7 November 2010 (UTC)

Neutrons are also found within nuclei. And they are stable there as well. Dauto (talk) 03:04, 5 February 2011 (UTC)

Reifying Language

The first paragraph has the following: "Neutron stars are very hot and are supported against further collapse because of the Pauli exclusion principle." The principle describes the force, it is not the force itself. Can this be rephrased so that it doesn't sound as if our theories cause the phenomena? —Preceding unsigned comment added by 24.22.166.163 (talk) 00:16, 10 December 2010 (UTC)

Neutron Star

The statement that "Neutron stars ... are supported against further collapse because of the Pauli exclusion principle." is incorrect. Pauli's exclusion principle is a very important physics principle, but in itself it does not generate the force that prevents a neutron star from further collapsing. There is a confusion here of a "principle" with a "force". — Preceding unsigned comment added by Macedonio5 (talk • contribs) 22:00, 4 February 2011 (UTC)

You're mistaken. The article is correct. Dauto (talk) 03:00, 5 February 2011 (UTC)

---

Formation

I wish this section could be considerably improved. It doesn't really contain any information on how a neutron star is formed.

---

— Preceding unsigned comment added by Macedonio5 (talk • contribs) 22:00, 4 February 2011 (UTC)

Cleanup for Properties section

The Properties section seems to have some discussion in it (e.g. the third paragraph calls the previous paragraph invalid.) RJFJR (talk) 18:03, 16 February 2011 (UTC)

Crust?

"The neutron star's density varies from below 1×109 kg/m3 in the crust,"

There is a crust? Or just a surface? — Preceding unsigned comment added by Darsie42 (talk • contribs) 18:57, 6 January 2013 (UTC)

• Yes, there is a crust, at mass densities up to 10¹⁴ g cm^-3. Depending on the temperature and magnetic field, the solid crust may or may not be covered by liquid ("ocean") and gaseous ("atmosphere") layers at still lower densities. Potekhin (talk) 16:58, 10 January 2013 (UTC)

1 mass?

The side illustration in Properties has the following "In natural units, the mass of the depicted star is 1". This does not state the units of mass. John W. Nicholson (talk) 16:42, 7 January 2013 (UTC)

• From the description in the primary source of this picture it follows that here the "geometric units" are implied. I have now fixed the wikilink there. Potekhin (talk) 17:08, 10 January 2013 (UTC)

Thanks --John W. Nicholson (talk) 02:10, 12 January 2013 (UTC)

Gravitational red shift?

With the idea of high mass and this statement "Even at 1 million kelvin, most of the light generated by a neutron star is in X-rays." I could not help but think of Gravitational red shift. How strong is it? Are x-rays shifted into visible light? John W. Nicholson (talk) 02:15, 12 January 2013 (UTC)

It's not near the Schwarzschild radius, so the red shift is going to be no more than 2. Still X-Rays, or far ultraviolet. — Arthur Rubin (talk) 05:36, 14 January 2013 (UTC)

$M_{solar}={M_{\odot }}$?

Is $M_{solar}={M_{\odot }}=1.98844\times 10^{30}\,kg$ correct? Currently, it is stated as $M_{solar}=1.98844\times 10^{30}\,kg$. — Preceding unsigned comment added by Reddwarf2956 (talk • contribs) 10:43, 12 January 2013 (UTC)

this is footnote 9

"Neutron stars, sugar cubes, and squeezed humans By Ankit | June 3, 2010 The wikipedia article on Neutron star says the following,

'The density of a neutron star is approximately equivalent to the mass of the entire human population compressed to the size of a sugar cube.'

I hope we can all agree that whoever came up with the idea of measuring the density of stars in the units of compressed human beings was a great visionary. Too bad for him, then, that wikipedia shackles his imagination by demanding facts. In this case, the above statement is followed by a superscript saying 'citation needed.' When someone has come up with such a great idea, I thought it's my moral duty to carry on his legacy and provide some concreteness to his ideas by doing some small calculations.

The problem we want to solve is to calculate approximately how many human beings need to be compressed to the size of a sugar cube in order to have the same density as that of a neutron star. A neutron star has a density 3 E^17 kg/m^3. One sugar cube, according to Yahoo answers, is half an inch (1.27 cm) long per side. Which makes the volume of the sugar cube to be 2.05 E^-6 m^3. If the sugar cube has the density of a neutron star, the total mass it should contain is 615 billion kg. Taking the average weight of a human to be about 80 kg, about 7.7 billion people are needed to be squeezed together in order to attain the astronomical densities we are talking about - which is not too different from the current population of the world.

If we are only talking about order of magnitude approximations, the wikipedia comment is acceptable. But we can go further. The current population of the world is about 6.8 billion and growing at about 1.1% which means that the magic figure of 7.7 billion will be reached sometime near 2021. At around that time, with the assumption of an average weight of 80 kg, the wikipedia statement would be truer than it is today. But then the assumption of 80 kg is obviously on shaky grounds. With so many kids who invariably fail at tipping the weighing machine beyond the 30 kg mark, our noble aim is but a mirage. For all these underweight human beings, it is upon McDonalds and Burger King to maintain the required balance. If it was not for these noble institutions, humanity would still be decades away from the day when sugar cubes, neutron stars and squeezed humans could be spoken of in one single sentence.

Anyway, I hope this little calculation added to our understanding of neutron stars. I think the citation that the wikipedia article required has finally been found" 76.218.104.120 (talk) 04:54, 6 February 2013 (UTC)

I don't think the sugar cube of humans is a helpful comparison, and now it has elicited its own citation. How about deleting this sugarcube stuff?76.218.104.120 (talk) 05:01, 6 February 2013 (UTC)

Source of the magnetic field

I simply wish to know the source of the magnetic field, what mechanism creates it? Misibacsi (talk) 08:53, 10 February 2013 (UTC)

An earlier edit contradicts this one. citation needed.

An earlier version of this article claimed that electrons and protons makes up a substantial fraction of a neutron star. The introduction here claims the star is "almost entirely" neutrons. A citation is needed. Can someone clean this terrible article up? There are random fragments of sentences and poorly structured paragraphs all over! I owuld do it myself if I felt I was competent to do so. 173.189.75.106 (talk) 10:27, 25 March 2013 (UTC)

Visible Spectrum

The article includes this: " In visible light, neutron stars probably radiate approximately the same energy in all parts of visible spectrum, and therefore appear white.". If it is approximately a black body, that is incorrect, the colour would be pale blue as shown below, just slightly more blue than Sirius (apologies for the large size, I can't see how to specify something smaller): George Dishman (talk) 11:22, 8 June 2013 (UTC)

Nuclear Pasta

It has been suggested in June 9th 2013 of the journal Nature Physics that there is evidence to suggest that matter in the core of a neutron star exists as a type of "Nuclear pasta", perhaps the article should be edited to include these findings? Sonicology (talk) 19:03, 1 August 2013 (UTC)

Giant Nucleus

This section states the nucleus is hold together by the strong force. I'm sure it's hold together by the weak force (or at least, as I've often read, "nuclear decay is mediated by the weak force"). Does someone know better (can they explain it)

Never mind. "Residual strong force" does not mean "not particularly significant force".

— Preceding unsigned comment added by 68.7.59.69 (talk) 20:54, 28 December 2013 (UTC) 

note 'a' is no longer valid

Does anyone know how to find this graph to be added to the page or should the note be removed?

A neutron star's density increases as its mass increases, and its radius decreases non-linearly. (NASA mass radius graph)

http://ixo.gsfc.nasa.gov/old_conx_pages/images/science/neutron_stars/ns_mass_radius.gif

Jgoemat (talk) 21:23, 5 December 2013 (UTC)

This is a current alternative for the EoS: Neutron star equation of state

File:Http://phys-merger.physik.unibas.ch/~hempel/mr sneos.png

default

George Dishman (talk) 13:00, 4 February 2014 (UTC)

Sentence from the lead

"having only the diameter of a city" - city is a loose term which can be a specific incorporated area, a community or even consolidated into something larger such as a prefecture. Therefore you can't describe something as being "the diameter of a city", as it could mean three miles or twenty miles. In fact, why not just put miles in the lead. Rcsprinter (chatter) @ 19:21, 14 January 2014 (UTC)

The size dpends on the equation of state which is poorly understood but the graphic I posted above shows the range is likely to be 11km to 15km. George Dishman (talk) 13:12, 4 February 2014 (UTC)

Temperature

Will a Neutron star ever "run out" of temperature? The article just makes comments to the temperature at the beginning of the life span of a Neutron star and that it cools in its first year, but not what happens afterwards. How long will it last until the temperature of a Neutron star reaches approximately 0 K?--31.17.153.69 (talk) 07:20, 25 March 2014 (UTC)

Nickel 62

From the article:

> Larger nuclei, particularly rich in neutrons, are formed, and materials that on Earth would be radioactive are stable in this environment, such as nickel-62.

Nickel-62 is stable on Earth, so I've removed the reference to it.

2601:0:AF00:226:A288:B4FF:FEC0:218C (talk) 14:23, 2 April 2014 (UTC)

Inaccurate figure given for surface gravity

I almost just removed the figures quoted because 1) they just seemed so implausible and 2) they were unsourced, but I figured it would be best to bring the issue up here. Maybe there is some factor at play that I just don't understand.

The entry reads "The neutron star's density also gives it very high surface gravity, up to 7×10^12 m/s^2". It also goes on to say "One measure of such immense gravity is the fact that neutron stars have an escape velocity of around 100,000 km/s". That doesn't make any sense to me. How can the surface gravity be 70 million times greater than the escape velocity? To add to that, if something were to be accelerated at 7×10^12 m/s for one second, wouldn't it be going 23349.5 times faster than the speed of light? I understand that if something were accelerated like that it wouldn't exceed the speed of light, but just add an insane amount of relativistic mass, but with those numbers wouldn't we be dealing with a super-supermassive black hole or something?

Apologies if this is just me not understanding physics and astronomy, but these numbers just don't make any sense to me. 50.174.135.49 (talk) 01:39, 27 June 2014 (UTC)

It's just you.

7×10^12 m/s^2 for gravity and 10^8 m/s for escape velocity doesn't seem out-of-line. To be precise, the Newtonian formula for escape velocity is ${\sqrt {2gr}}$; substituting r = 1.2×10^4 m and g = 7×10^12 m/s^2 , you get an "escape velocity" of 4.1×10^8 m/s. The article mentions the possibility of an escape velocity greater than c, making it a black hole. I don't presently have access to the formulas for relativistic gravity and escape velocity; suffice it to say the the Newtonian approximation is not adequate. — Arthur Rubin (talk) 04:36, 27 June 2014 (UTC)

• The numbers are not incorrect. The figure "7×10¹² m/s^2" does not imply a constant acceleration measured in an inertial reference frame during exactly one second. In fact, it is a measure of gravitational force per unit mass. The first number corresponds to a neutron star with mass of 2.5 Solar masses and radius 10 km. The second is just an order of magnitude, not an exact number. However, the first number also cannot be determined that precisely, given the current uncertainties in the neutron-star equation of state, therefore I've replaced it by an order-of-magnitude estimate also, namely "~10¹³ m/s^2". As concerns sources, about a half of the sources listed in the "References" section will give you this order of magnitude. I have now added just one of them. Potekhin (talk) 09:28, 27 June 2014 (UTC)

Thanks for the explanation, folks. Now I'm really glad I didn't mess up your article out of my own ignorance and incredulity! 50.174.135.49 (talk) 17:38, 27 June 2014 (UTC)

It looks like the maximum size of neutron stars is about 2 solar masses. Measured radius is about 10 – 15 km? A 2 SM neutron star has a Schwarzchild radius of 6 km which should contain light up to 12 – 18 km, so wouldn’t a 10-km neutron star have some light containment? There should be formulas for the effectiveness of light containment of a neutron star or black hole based on internal star radius. A hypothetical compact star or internal black hole star of 3GM/(c^^2) radius should contain light, but not as effectively as a Schwarzchild radius star or point singularity. When matter falls into a black hole, wouldn’t infalling matter eject more radiation (jets?) if the black hole contained a finite sized star instead of a point singularity? 72.69.11.171 (talk) 16:56, 26 July 2014 (UTC)BG

N

wwwwwwwwwwwwwwwwwwwwwwwww Bold text — Preceding unsigned comment added by TheBluePotato646 (talk • contribs) 16:26, 6 December 2014 (UTC)

Maximum neutron star mass is about 2 solar masses

NS mass is limited by some process, and measured data indicates this is about 2 solar masses. (My vote is this is because above 2 SM neutrons in the core collapse into mostly radiation and some quark matter .... the radiation would exit the star and the quark matter would quickly recombine to neutrons.) Apparently the radius of a neutron star does not increase much with mass, so IF a stable neutron star 3 SM or greater existed it would partially contain light and we could call it a black hole. 72.69.11.171 (talk) 23:41, 31 July 2014 (UTC)BG

Dated?

From my reading the current thinking is that collapsed stars with a mass over about 2 MSun are not composed of neutrons but either have quark matter cores or are entirely quark matter. That makes the designation "neutron star" inappropriate. http://arxiv.org/find/astro-ph/1/ti:+AND+quark+star/0/1/0/2012,2013,2014/0/1?per_page=100 Is this too new for inclusion? Qemist (talk) 03:08, 25 April 2014 (UTC)

As I understand the situation, this is still purely hypothetical, since the equations of state of quark matter are poorly known, both experimentally and theoretically. Any quark matter content is still purely hypothetical, no matter how likely such hypotheses are based on collider experiments. There is no true substitute for a direct detection. Furthermore, Wikipedia or Wikipedia talk is not a forum for settling scientific questions such as if compact stars should be called neutron stars or not; as long as the scientific community calls them neutron stars, they are neutron stars here also. Also, arxiv is not a reliable source, and much less a scientifically reliable source, because no scientific peer review is required to publish there. (Not even all peer-reviewed articles are good!) Moreover, search POST actions cannot be sources in the first place. Sorry for the broadside, but again, an encyclopedia must be much more selective than a general text such as a blog or magazine. --vuo (talk) 20:49, 25 April 2014 (UTC)

Thanks but I was hoping for a response from someone more knowledgeable about the topic than I. Qemist (talk) 06:07, 26 April 2014 (UTC)

Recent observations indicate neutron stars over about 2 SM do not exist. See recent edits and comments below. Apparently there are no compact stars between about 2 - 5 SM. The smallest observed black holes are 5 SM and they could be quark matter and radiation. There might be a simple explanation why there are no black holes smaller than 5 SM: A collapsing 4 SM neutron core is about equal to its Schwarzchild radius (12 km) and about 5 SM total is contained. A hypothetical about 3 SM neutron star isn't strong enough to contain its contents Schwarzchild style but collapses and ejects radiation as it pops down to below 2 SM where it is stable. 72.69.11.171 (talk) 14:26, 7 August 2014 (UTC)BG

You should indent your responses appropriately. I couldn't make much sense of what you said. Could you provide some links? arxiv is fine. Qemist (talk) 01:17, 10 August 2014 (UTC)

Links on what specifically? Maximum observed mass of neutron stars? Minimum observed mass of black holes? — Preceding unsigned comment added by 72.69.11.171 (talk) 06:54, 10 August 2014 (UTC)

velocity units

The article makes several references to acceleration, escape velocity and speed of light using km/s. The speed of light is just under 300,000,000 m/s. It looks like some of the units are incorrectly marked km/s. From the text: ..."and would do so at around 2000 kilometers per second." Sherumgroup (talk) 16:42, 20 August 2014 (UTC)

No it isn't. 2000 km/s is just 0.007c. Also, if you do a rough recalculation you'll see the reference is correct. 1 solar mass (2e30 kg) in a 14 km sphere gives you a local g of 1.334e20 N/kg from Newton's law of universal gravitation. Given that the kinetic energy density (E_k/m) of an object dropped from a height is the g times distance (work = force × distance, divide by mass), you can calculate the velocity by solving the formula for kinetic energy, E_k/m = ½v², for v. This gives v = √2gh, and inserting g = 1.334e20 N/kg and h = 1 m gives you 2.333e6 m/s, or about 2000 km/s, just as in the source. Objects move up to ca. 70 km/s even in the Solar System, so this is just two orders of magnitude higher. --vuo (talk) 19:08, 20 August 2014 (UTC)

Mass range in lede

The range of masses in the lede is confusing and probably wrong. It states compact stars of less than 1.44 solar masses are white dwarfs, yet there are neutron stars in the literature with well constrained masses less than that, e.g. the companion to PSR J1756-2251 (1.230+/-0.007 MS), PSR J0737−3039 B (1.25 MS), and PSR J1906+0746 (also 1.25 MS). Then it states that compact stars between this limit and 3 MS "should" be neutron stars, but later that the maximum mass of a neutron star is about 2 MS. That is contradictory as to the state of objects with masses between 2 MS and 3 MS. Qemist (talk) 02:14, 10 August 2014 (UTC)

I didn't write the article but added some corrections, probably not all the corrections that would be desirable. 2 SM is the maximum observed mass of neutron stars based on a significant data base. The way I read it is 3 SM neutron stars might be possible based on the TOV equation. I think if the article says "neutron stars are" than what should be presented is observational data and not theoretical data, no disrespect to the theorists. I'm not sure the TOV equations allow up to 3 SM neutron stars (maybe the article is wrong on this) but if TOV equations predict this its OK to state it.

Please indent your responses appropriately. I agree observational data should take precedence over theoretical predictions and that the article should clearly distinguish between them. At the moment the article presents too much theory as fact. At the moment any object that is too small and dense to be a white dwarf and isn't a black hole is called a "neutron star". Their composition is unobserved and the idea that they are composed of neutrons is based on theory. There are competing theories that suggest they are composed at least partly of some sort of non-baryonic "exotic matter". The fact that no neutron stars with masses constrained to be strictly greater than 2M_S have been observed does not mean that they don't exist; it may be they just haven't been sufficiently well observed. There are suggestions that some "black-widow" pulsars have higher masses, e.g. PSR J1311–3430 and PSR B1957+20. Qemist (talk) 11:42, 10 August 2014 (UTC)

Don't be too harsh on this good article, its a field still in flux. You make a profound point about the composition of "neutron" stars. (My personal thoughts are neutrons are probably about right.) Thanks for the info on these 2 stars .... the large mass is disturbing. I will take the safe cowardly route and for now modify the max observed mass of neutron stars to "about 2 SM". There is good reason to be skeptical a 2.4 SM compact star exists but if a 2.4 SM compact star existed it should be able to have some relativistic matter containment. Then it might be something between a neutron star and a black hole, neither a neutron star nor quite a conventional black hole, and it probably shouldn't be called a neutron star. Maybe the correct max mass for neutron stars is close to 2.0 SM. Food for thought. 72.69.11.171 (talk) 13:07, 10 August 2014 (UTC)

The figure of 2.4 SM is incorrect. Do you have a source for this other than the Black Widow Pulsar Wiki article? From this source the lower mass limit for this neutron star is about 1.6 SM: http://arxiv.org/abs/1009.5427 See the Wiki articles on PSR_J1614-2230 AND PSR J0348+0432. 72.69.11.171 (talk) 22:28, 13 August 2014 (UTC)

Lets consider for now 2$M_{\odot }$ is the max for a neutron star and 5$M_{\odot }$ the min for a black hole. A 5$M_{\odot }$ 22.5-km radius ultra-relativistic star has about the same gravitational acceleration and core pressure of a 2$M_{\odot }$ 13-km neutron star, yet a 5$M_{\odot }$ 22.5-km ultra-relativistic star theoretically contains light and a 2$M_{\odot }$ 13-km neutron star does not. (Note 25-km is 1.5 times the Schwarzchild radius) For an ultra-relativistic star gravitational acceleration and core pressure decrease as size increases. It does not collapse. 72.69.11.171 (talk) 14:32, 14 August 2014 (UTC)

Radius? What is radius in the case of a potential singularity? Do you mean circumference divided by 2π? (I know it's called Schwarzchild radius that doesn't mean there is an actual radius involved.) In any case, "contain light" is an interesting term, also. If it's larger than 1.0 times the Schwarzchild radius, it's not necessarily "black"; photons from the surface can escape. If within 1.5 r_s (and the field equations agree with the Schwarzchild solution outside the body, which is not a foregone conclusion), then there are closed photon orbits. — Arthur Rubin (talk) 00:56, 15 August 2014 (UTC)

I'm saying there is no point singularity but instead a star composed of ultra-relativistic material and photons of radius 1.5 r_s. This star acts radically different (size and pressure wise) from other stars in that its radius is proportional to its mass, unlike a neutron or conventional star. The basic equation of state for quark matter or photons in this star is the pressure P = (pc^2)/3, where p is the energy density. The supporting energy (viral energy) of material in this star = ∫PdV = (mc^2)/3, meaning a whopping 1/3 of the mass energy of this quark/photon mix is used just to oppose the force of gravity, but its still only 1/3 of mc^^2 and not 1.0 or 0.67 or even 0.5 of mc^^2. Ultra-relativistic material or photons can't escape the surface of a 1.5 r_s star. 72.69.11.171 (talk) 16:37, 15 August 2014 (UTC)

That's just wrong. Photons can escape the surface of a R;; = 1.5 r_s star. I'm willing to believe that there are situations in which light (null geodesics) cannot escape but a particle (time-like curve) can escape, but it's not as simple as R = 1.5 r_s. — Arthur Rubin (talk) 16:07, 16 August 2014 (UTC)

Well, somebody is wrong. Infalling material can have mc^^2 available but not contained material. Do you think the thermal energy (pressure creation ability, the ability to do work) of photons or ultra-relativistic material is (mc^2) or (mc^2)/3 ? I also used to think the pressure of light was pc^^2 when I guessed at it 3 years ago. A better way of explaining it is that ultra-relativistic material of mass m only has (mc^^2)/3 available to push itself out of a star. BTW the exact radius I came up with for this star is 1.66 r_s and not 1.5 which some people may find confusing. I should probably use 1.66 instead of the 1.5 approximation. People might be confused by the 1.5 figure because that is coincidently the accepted radius for orbital light for a black hole. If you check into it a black hole can contain some types of light to within 3X the Schwarzchild radius.

A 1.66 r_s star would explain the huge amounts ejected from black holes.

I was at a NYU university forum on black holes 2 months ago and although a 1.5 r_s star was not accepted, anyone expressing an opinion (many physics doctorates were there) said a 1.5 star would contain light, but not as well as a 1.0 r_s star or point singularity. Note they teach a point singularity is reality and a star smaller than 2.0 r_s is impossible based on the TOV equation, but I think the TOV equation is wrong because it predicts collapse of a 0.7 SM neutron star and TOV does not even acknowledge a back pressure of (pc^^2)/3. Note a 1.66 r_s star doesn't even contain orbital light; light it contains would just about have to hit it bulls eye. But it would bend nearby light similar to a point singularity. Light is easier to contain than some might think. A 2 SM neutron star comes dang close and a hypothetical 3 SM neutron star would contain light. Intelligent people would logically but incorrectly therefore conclude that as some mass is added to a 2 SM neutron star it would collapse directly into a black hole.

Schwarzchild proposed a point singularity that mathematically contained light. That doesn't mean a point singularity is reality. A small enough finite sized star of enough mass would also contain light. 72.69.11.171 (talk)BG — Preceding undated comment added 17:52, 16 August 2014 (UTC)

Please remember that the purpose of this page is to discuss improvements to the article, not to have a general discussion of the topic. Nothing you heard at a seminar (let alone your own opinions), could be a suitable verifiable basis for inclusion in the article. Qemist (talk) 04:17, 17 August 2014 (UTC)

OK you are right this has probably diverged too much. But neutron stars being limited to about 2.01 SM is relevant. Theories on why this is so should be added to the article if those theories are sourced. I'm sure you agree why black holes start at 5 SM and not directly from a >2 SM neutron star is relevant, and understanding this will require understanding both >2 SM neutron stars and 5 SM black holes 72.69.11.171 (talk) 20:30, 17 August 2014 (UTC)BG

BTW, there is an interesting formula about the radius and radiated energy from infalling matter into a neutron or compact star: Accretion energy conversion efficiency = (Schwarzchild radius)/(2R) ..... where R is the radius of the star. (see: http://www3.mpifr-bonn.mpg.de/staff/mmassi/lezione2WEdd.pdf ) If a black hole is a point singularity its image should be different than that of a neutron star. 72.69.11.171 (talk) 19:07, 1 October 2014 (UTC)BG

Lede clutter

This article is suffering from a rather serious case of ledeclutter, at five paragraphs with comparisons to the sun, Manhattan, atomic nuclei, a 747, sand, a matchbook, and rock, as well as a lot of specific information (Neutron stars have overall densities of 3.7×1017 to 5.9×1017 kg/m3 (2.6×1014 to 4.1×1014 times the density of the Sun) etc. I propose consolidating the important information into a nice three or four paragraph summary and moving details to the body. Comments? A(Ch) 08:48, 13 January 2015 (UTC)

Copyright problem removed

Prior content in this article duplicated one or more previously published sources. Copied or closely paraphrased material has been rewritten or removed and must not be restored, unless it is duly released under a compatible license. (For more information, please see "using copyrighted works from others" if you are not the copyright holder of this material, or "donating copyrighted materials" if you are.) For legal reasons, we cannot accept copyrighted text or images borrowed from other web sites or published material; such additions will be deleted. Contributors may use copyrighted publications as a source of information, and according to fair use may copy sentences and phrases, provided they are included in quotation marks and referenced properly. The material may also be rewritten, but only if it does not infringe on the copyright of the original or plagiarize from that source. Therefore such paraphrased portions must provide their source. Please see our guideline on non-free text for how to properly implement limited quotations of copyrighted text. Wikipedia takes copyright violations very seriously, and persistent violators will be blocked from editing. While we appreciate contributions, we must require all contributors to understand and comply with these policies. Thank you. Znbn (talk) 22:39, 19 January 2015 (UTC)

I have removed a large section of text from the "Properties" section that appears to be a copyright violation, directly lifted from the Philip's Astronomy Encyclopedia (2002), pg 281-282.

Nearest neutron star

What is the nearest neutron star? In the see also section it says PSR J0108-1431 (424 ly), but in the body RX J1856.5-3754 (400 ly) is mentioned alongside it. --JorisvS (talk) 09:00, 1 February 2015 (UTC)

Mass examples in lede are blatantly incorrect

The approximate mass of a matchbox of neutron star material is blatantly incorrect as the quoted density of a neutron star is 3.7*10^14 tons/m^3, which would make a soda can (355ml) weigh 3.7*10^14*355/10^6 or 131 gigatons, yet the lede claims 5000 gigatons for a matchbox. That's a big matchbox! The average density of rock is ~ 2.7 tons/m^3, or 2.7*10^9 tons/km^3 or 2.7 gigatons, yet the lede claims 1 km^3 of rock weighs 5000 gigatons! A soda can of neutron star material would weigh close to 3.7^10^14*355/10^6/2.7/10^9 = 48.6 km^3 of rock. David.Anderson.unique (talk) 13:49, 5 July 2015 (UTC)

Protection edit request on 31 June 2015

To avoid anymore vandalism if not any. — 73.47.37.131 (talk) 21:27, 31 July 2015 (UTC)

??? — Martin (MSGJ · talk) 21:36, 31 July 2015 (UTC)

Problem with temperature

Please add temperatures that normal people can understand. Example: What does a surface temperature around "~6×10⁵ K" mean? Can we have plain numbers please. Not everyone knows that K means Kelvin, and even less people are able to figure out the value of "10⁵". Urbanus Secundus (talk) 20:59, 13 June 2015 (UTC)

Why should a page written in standard english cater to the lowest common denominator? This isn't a pop science book, you're supposed to know what the basic terms mean in beforehand. — Preceding unsigned comment added by 134.90.152.252 (talk) 15:27, 9 December 2015 (UTC)

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I'm concerned about these 2 sentences at the beginning of the article: "A neutron star has a mass of at least 1.1 and perhaps up to 3 solar masses (M☉),[1][2] though the highest observed mass is 2.01 M☉. Neutron stars typically have a surface temperature around 6×105 K."

Maybe it should say "A neutron star has a theoretical mass of 1.1 - 3 solar masses". Also giving one specific temperature value is misleading.173.56.18.42 (talk) 14:54, 8 February 2016 (UTC)BG

Neutron Star Nucleosynthesis

It is stated on the Wikipedia page for gold that it is most likely made by colliding neutron stars. I came to this page to find out what other elements in the periodic table might be made by these events. This section needs to be created

Amphibio (talk) 17:07, 24 February 2016 (UTC)

Context for numbers

"There are thought to be around 100 million neutron stars in the Milky Way, a figure obtained by estimating the number of stars that have gone supernova." How many stars in the Milky Way total? Percent of whole might give me some insight about how rare this is Cegandodge (talk) 19:31, 18 March 2016 (UTC)

Observed neutron star upper mass limit of 2.01 M_☉

A logical explanation for neutron star mass being limited to about 2.01 M_☉ is the collapse of core nuclei. Note that at about 2 M_☉ and 12-km radius the relativistic gravitational core pressure is about equal to (rho)(c^2)/3. A logical equation for nuclei disintegration is: proton → positron + 938MeV. This reaction should either heat the star or result in a 450MeV maximum electrically neutral positron-electron jet. 108.30.181.243 (talk) 12:09, 11 June 2016 (UTC)BG

Please note that article talk pages are for discussions about the article, not about the subject. See wp:Talk page guidelines. - DVdm (talk) 12:38, 11 June 2016 (UTC)

Equation appears to be dimensionally incorrect

The equation

$BE={\frac {885.975\,M_{x}}{R-738.313\,M_{x}}}$

appears to have mixed dimensions in the denominator.
R has a dimension of length
$M_{x}$is dimensionless — Preceding unsigned comment added by 50.45.15.139 (talk • contribs)

That equation is only valid if it has R in meters. The numbers 885 and 738 have units of meters. Headbomb {talk / contribs / physics / books} 00:51, 26 September 2016 (UTC)

Strong force supports neutron stars against collapse

The article's editors continually write that neutron degeneracy pressure supports the neutron star against collapse. This is mostly untrue and should not be the sole reason given here. The editors are generally working from the false analogy that if a white dwarf is supported by electron degeneracy pressure, the neutron star must be supported by neutron degeneracy pressure. Note that none of their sources actually state that neutron degeneracy pressure supports the star - it's just "assumed."

Real neutron stars are supported against collapse mostly due to the strong nucleon-nucleon force. (No, the strong force does not act only in attraction - see https://en.wikipedia.org/wiki/Nuclear_force.) At the short nucleon-nucleon distances within the core of a neutron star, the strong force will act to repel nucleons (here, mostly neutrons) from one another. This repulsion - unrelated to degeneracy pressure - is stronger than degeneracy pressure within neutron stars. It supports the neutron star against collapse.

Sources: http://www.astro.princeton.edu/~burrows/classes/403/neutron.stars.pdf (page 3) "...using the relativistically correct equation of hydrostatic equilibrium (eq. (5)), and assuming a non-interacting degenerate gas of neutrons, Oppenheimer & Volkov (1939) derived a maximum neutron star mass of 0.7 M⊙, ∼eight times smaller. Observed neutron-star masses are clearly larger than this. The reason is that the strong repulsive nuclear force trumps neutron degeneracy pressure by a wide margin, resulting in less compact and more rigid structures supported by a stiffer EOS."

https://www.astro.umd.edu/~jph/A320_White_Dwarfs.pdf (page 10) "At densities of ρ ∼ 10^15 g cm−3, neutrons are not an ideal gas. These are the densities we find within an atomic nucleus, and the neutrons interact with one another via the strong force. Thus we see that to model neutron stars we need the TOV equation and an equation of state that includes not only degeneracy but the nuclear forces between the neutrons."

http://www.aanda.org/articles/aa/full/2001/46/aa1755/aa1755.right.html "The EOS is predominantly determined by the nuclear (strong) interaction between elementary constituents of dense matter."

http://www.rpi.edu/dept/phys/Courses/Astronomy/NeutStarsAJP.pdf Demonstrates that the strong force must be considered. The overall picture is not simple and not totally understood, as our knowledge of nucleon-nucleon interactions is incomplete.

I look forward to seeing discussion of the strong force's role permanently and prominently displayed in this article.

60.45.238.24 (talk) 15:28, 4 October 2016 (UTC)

Well with the nuclear force (which has slightly different semantics to the strong force) it is assumed that quantum degeneracy (hence Pauli's exclusion principle) is responsible for repulsive force between nucleons. But papers also postulate an additional negative nuclear force to account for neutron stars over about 0.7 solar masses. So I guess this could also be added, but if you do so please reference with inline citations! I think that is why it gets removed. If you don't know how to do this then ask me how. --Jules (Mrjulesd) 21:29, 4 October 2016 (UTC)

Jargon needs definitions or links

The terms AP4, MS2, and "(for EOS FPS, UU, APR or L respectively)" are used with no definitions nor links to anything which might explain them. It makes those passages less than helpful.

P.S. to the authors: Thanks for an otherwise nice article. — Preceding unsigned comment added by Oldmeat (talk • contribs) 01:36, 1 March 2017 (UTC)

Source of energy?

As we all know, with regular stars, nuclear fusion takes place place in their cores, and this nuclear fusion is what produces the energy emitted thereby.

Neutron stars also produce protons, but I wouldn't guess that nuclear fusion is taking place in their cores.  Would I be wrong to assume it's not?  And, assuming I am correct to guess that there is no nuclear fusion taking place therein, the question then remains: what produces the energy emitted by neutron stars?

If you know the answer to these questions, please help improve this article by adding details about neutron stars' source of energy.

allixpeeke (talk) 15:39, 27 June 2017 (UTC); augmented 12:08, 30 June 2017 (UTC)

You can ask at the wp:reference desk/Science. Here we must discuss improvements to the article, not the subject. See wp:Talk page guidelines. Cheers and good luck. - DVdm (talk) 15:41, 27 June 2017 (UTC)

Sorry if my purpose was unclear.  (I've now augmented my previous question to make my intentions clearer.)  I was discussing improvements to the article.  By pointing out that there is an interesting aspect of the science behind neutron stars not yet covered in this article, I am giving those with the expertise requisite to improve the article an area upon which to focus their future edits.  Cheers, allixpeeke (talk) 12:08, 30 June 2017 (UTC)

Ok, fair enough. I struck my comment . - DVdm (talk) 12:44, 30 June 2017 (UTC)

Long-term evolution of neutron stars

A short section explaining what the long-term evolution of neutron stars is expected to be would be nice. Can a neutron star cool down to near zero absolute and remain stable against gravitational collapse? Ho wmuch time would the cooling take? (I'd expect this to be orders of magnitude more than the current age of the Universe) Urhixidur (talk) 17:00, 29 September 2017 (UTC)

Images from MS Paint

Really, this is accepted quality for wikipedia? I expected better188.175.76.2 (talk) 07:24, 16 December 2017 (UTC)

Please feel free to recommend how the article can be improved. --‖ Ebyabe ^talk - General Health ‖ 07:58, 16 December 2017 (UTC)

Unproductive Drive-By Comment

Transient condensates are core properties ranging from Axion matter to various Parton matter to Quark matter to Neutron matter. This Condensate matter makes up over 95% of all matter in the infinite universe. The core does not undergo fusion. It keeps on attracting matter into it. In the case of our Sun its core will photo-disintergrate atoms such as Fe(and all other) to neutrons and protons(change to Neutron) that would become part of the core. The gauge field on the lattice is the resultant property forming a dipolar electromagnetic effect producing vortices, that expel neutrons into the solar envelope that change to protons that than take part in fusion reactions H+H= Helium etc forming all the elements. The Sun's energy is produced by the core 65%, Fusion reactions within the solar envelope 35% and about 5% fission. It all about the core and its properties. Images created by condensates as in the Kilonova hour glass and the release of condensate droplets that produce giant bubbles. — Preceding unsigned comment added by Harry Costas (talk • contribs) 00:20, 2 January 2018 (UTC)

Weight of the Moon ?

A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg (that is 1100 tonnes per 1 nanolitre), about 900 times the mass of the Great Pyramid of Giza. In the enormous gravitational field of a neutron star, its weight would be 1.1×1025 N, which is about 15 times the weight of the Moon.[c]

>>> This seems odd to me ? Are we referring to the weight of the moon specifically as if an object of its mass is effected by earth's gravity ?

This part seems to contain an often-quoted error. The Giza pyramid weighs about 6 million tons. A teaspoon of neutron star material weighs about 10 million tons. How could 6 million x 900 = 10 million? — Preceding unsigned comment added by 162.227.178.143 (talk) 23:55, 4 December 2018 (UTC)

But , wouldnt an object of sufficient mass also attract the Earth towards itself with its own gravitational field , thus increasing its relative Weight ? — Preceding unsigned comment added by 2607:FCC8:AB49:2200:B19A:6BCE:F4C3:ABA6 (talk) 22:24, 8 December 2017 (UTC)

Please note that the Moon orbits the Earth. As such, it is the most massive object currently in Earth's gravity - after Theia up and collided with the Earth. --vuo (talk) 13:25, 8 January 2018 (UTC)

Percent of neutron stars in milky way

The article states, "At present, there are about 2,000 known neutron stars in the Milky Way..." I was going to contribute an estimated percentage of neutron stars, as compared to the total estimated number of all stars, in our galaxy, but the range from NASA to Swinburne sources were a billion down to 100,000. NASA's figure is from 2007 and Swinburne's much more recent, but perhaps another editor can figure out the most credible current estimate. This is relevant not only for curiosity sake but especially now that the supernova origin of heavy elements theory is disfavored for a neutron star/black hole collision hypothesis. Bob Enyart, Denver KGOV radio host (talk) 21:42, 27 June 2019 (UTC)

Energy Source

In response to an old request, I have begun to find information regarding the energy production of neutron stars. I agree this is an improvement to the article itself as this important subject seems non-existent referencing this type of star. It can also help make sense of the star's internal structure, why it is so could be extrapolated further. This will not be a heavy edit since there is not much discussion in the literature about how neutron stars produce their energy, and it is the first time this topic has been attributed to properties of a neutron star in this article to allow further iteration and collaboration.

Neutron stars lose heat energy by emitting neutrinos and electron conduction within. Over time this is radiated away from the star in the form of neutrinos and X-rays. Most emissions are not thermal, at around one million Kelvin it has most radiation being high energy x rays or UV rays. Neutron stars are not black bodies, so it does not emit very much thermal energy which has caused speculation as to how they produce such high energy.

ChromeDragon (talk) 23:23, 15 September 2019 (UTC)

Citation

I removed a "Citation needed" tag from the first intro paragraph. There is a reference at the end of the next sentence. Wikipedia Style asks that editors place as few copies of a single reference as possible, and in particular if two, or several, contiguous sentences, each with a distinct fact, are all supported by the same reference, then Wikipedia asks that that reference be placed once at the end of the contiguous sentences. Unless the editor who inserted the "Citation needed" tag has actual knowledge that the reference at the end of the next sentence does not support the fact they tagged, they should not tag it. Nick Beeson (talk) 15:31, 17 September 2019 (UTC)

moved to TP - ref?

I have moved this statement here pending a reference - it was tagged 13 months ago: " It is statistically probable based on known populations that there is at least one neutron star within 10 parsecs of the Sun, significantly closer than the current nearest known neutron star. " — Preceding unsigned comment added by HammerFilmFan (talk • contribs) 18:50, 17 May 2020 (UTC)

Seems reasonable, until a source is found. --Jules (Mrjulesd) 13:57, 18 May 2020 (UTC)

I think this was take from this paper. Ruslik_Zero 20:06, 18 May 2020 (UTC)

Wikipedians cannot do simple volume calculation

"... the same weight as a 0.5 cubic kilometre chunk of the Earth (a cube with edges of about 800 metres)"

A 0.5 cubic km would have edges of exactly 500 metres... Just saying. 2403:6200:8856:563C:D011:4BA2:409E:1E (talk) 04:53, 16 November 2020 (UTC)

Um, no. (0.8 km)³ = 0.512 km³. Volume does not scale linearly with diameter. TornadoLGS (talk) 04:57, 16 November 2020 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion

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Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 16:28, 7 April 2021 (UTC)