Talk:Neutron star

Escape Velocity

For the escape velocity of the neutron star, I wonder, was that found by using the traditional newtonian physics equation for gravitational potential energy, converting it into kinetic energy and finding the escape velocity? [ sqrt((2GM)/r) ] However, as it says, 150,000 km/s is half the speed of light, wouldn't you have to use general relativity to figure it out instead? Mercury has a much lower speed, yet even its orbit has certain relativistic effects. Are there any math geniuses that can confirm or refute the escape velocity of 150,000 km/s? It isn't important but it's sort of interesting to think about and I'd like to know. —The preceding unsigned comment was added by 72.59.2.127 (talk • contribs) .

Internal structure and questions

Question: what is the internal structure of a neutron star like? Where are the boundaries between neutronium, degenerate and normal matter located? What percentage of the stars mass or volume are each? What is degenerate matter? What do the boundaries between the layers look like? What is there shape? (I suppose some of these questions may not have answers yet...) -- SJK

The following are the transitions between the states you mention: it depends on the density: (in g/cm^3)

~1 x 10^6 - electrons become relativistic

~1 x 10^9 - nutronization

~4 x 10^12 - neutron degeneracy pressure dominates

~2 x 10^14 - nuclei dissolve

~4 x 10^14 - pion production: superfluid neutrons, superconducting free protons, relaticistic free electrons, other elementary particles (not well known, possible production of exotic matter) —This unsigned comment was added by 70.25.24.27 (talk • contribs) on 05:10, 23 March 2006.

I can answer some of these questions...

From what I've read, neutron stars don't have any internal structure. It's just neutrons, all the way through. The degenerate and normal matter layers are just a few meters thick on the surface. So it's something like 110% plus percent of the star's mass is neutrons. This is because nothing else can possibly exist inside there.

It's wierd to think about them. A neutron star is essentially a titanic atom, which is held together by gravitational force instead of the weak nuclear force. -- The_ansible

that is incorrect - it is the [strong nuclear force] that binds nucleons together, not the [weak nuclear force].

As I corrected in the article, a neutron star is not like an atomic nucleus, because it is not just protons and neutrons, but almost all neutrons inside and whatever on the surface (assuming you're correct in that notion).

Also I think you meant the residual strong force, the weak force is the mediator of beta decay, the breaking up of neutrons into electrons etc., the opposite of what happens in a neutron star. Rmrfstar 00:36, 5 Apr 2005 (UTC)

Actually, I would disagree. The outermost layers of a neutron star will consist of neutrons in a sort of crust, but as you look further inside, the density and pressure get much higher, and the neutron structure dissolves to leave a sort of deconfined quark core. Around this phase transition density, it is energetically favourable to 'create' hyperons and other baryons. There is a lot more to a neutron star than just neutrons. A heck of a lot less than 99.9%. Besides, for interactions between the neutrons you will need sigma, omega and rho mesons.

The comment "nothing else can possibly exist inside there" is most certainly incorrect as far as the most recent theories go. As for the exact structure of a neutron star, that is purely left up to theory, though limits can be imposed based on observations. If you could crack a neutron star open to have a look, please let me know! -- JDC

Neutronium and quark matter

Whoever deleted the term 'neutronium' from the main page -- if you are saying not to use that term, note we already have a page neutronium. Secondly, I find your new version hard to follow -- whats an 'iron layer'? Finally, but 'quark matter' you mean what? -- SJK

more on neutronium - http://www.physics.uq.edu.au/people/ross/ph227/evolve/whitey.htm

"quark matter" is probably a reference to strange matter

Sorry, it was made in a haste. Iron layer is a thin crust of metalic iron, by quark matter i mean a soup where not even individual neutrons exist, but a mixture of quarks of different kinds. "strange" matter is matter partially composed by "strange" quarks. What i tried to emphasize is that there was a comtinuum of compositions inside a neutron star, and that telling "a crust of degenerate matter and and interior of neutronium" was an oversimplification that also hided the fact that there is no aggreement respect to what's in the core. AN

Ok. i can live with that for the time being. AN

You see - we actually can all get along :) - MMGB

Extraterrestrials

From the article:

"When neutron stars were first discovered, they were believed to be evidence of extra-terrestrial intelligences. Because of their highly regular pattern of emmisions, they were initially though to be beacons of some type."

I don't think that pulsars were ever seriously thought to be evidence of extraterrestrial intelligence, at least not by the researchers who were actually investigating them. The first pulsar discovered was dubbed "BEM-1" (Bug-Eyed Monster 1) as a joke by its discoverers, if I recall correctly. But since this is all from memory, anyone have any references handy? Bryan Derksen

question

As a non-physicist, how does this sentence:

Neutron stars are the densest objects known

relate to black holes? Thanks, [[User:Meelar|Meelar (talk)]] 19:04, Sep 10, 2004 (UTC)

I'm not well read in astrophysics, but mass and [density] are two separate things. Compare traffic in New York to traffic in California. New York has tons of traffic jams and everyone is stuck together. California might have more cars overall, but they're more spread out for the main part. The same is true for black holes and neutron stars, black holes have more mass, but neutron stars are more closely packed. Presuming the statement above is correct. If anyone more knowledgable can confirm this that would be good.

User:zdude255

I believe you are correct in your distinctions between mass and density, however I think a black hole is still infinitly dense, even if you determine it's size by it's Schwartzchild radius. Rmrfstar 00:38, 5 Apr 2005 (UTC)

It's easy to show that it's not infinitely dense if you're using the size of the event horizon, simply by observing that both the mass and the radius are finite and nonzero. Divide the mass by the volume to get density. While black holes the mass of a star are extremely dense, the fact that black hole radius is directly proportional to mass means that density drops off as the inverse square of mass. A supermassive black hole containing a billion solar masses would be only a little denser than air. In practice, calculating density this way doesn't tell you anything terribly useful, but it's interesting to think about. --Christopher Thomas 08:50, 2 March 2006 (UTC)

The real problem, though, with black holes, is that we have never seen a black hole; no one has, because it is impossible to observe one, and we can only see their effects. So, in a sense, black holes are not "known", per se, while neutron stars can be and have been observed directly, even if what we know is, in fact, based on mostly mathematical models. —The preceding unsigned comment was added by 67.160.131.117 (talk • contribs) on 08:04, 2 March 2006.

We haven't observed neutron stars directly, any more than we've observed black holes directly. In both cases, we see that there's a massive, compact object affecting nearby matter. Mostly what we see are the accretion disc, a black hole's polar jets, radio and microwave emissions from particles caught in a neutron star's magnetic field, and glowing from infalling matter impacting the surface of a neutron star (which is absent for black holes, as they have no surface to impact on). From the motions of any companion stars, the mass of the neutron star or black hole can be estimated. From the temperature and velocity of various parts of the accretion disc, its radius can be estimated (though often it's just assumed to be in the expected range for the given mass, as it's difficult to get a reliable direct measurement).

For that matter, nobody's directly observed an "electron"; only measured its effects. Yet we're still reasonably confident that electrons exist. --Christopher Thomas 08:50, 2 March 2006 (UTC)

Indeed, one must define "observe" carefully when speaking of physics. Very little in physics is directly observable by the human eye, but much is quite certain nonetheless. Most of steller physics is known through taking spectra of stars for example - we don't "see" what stars are made of, but the science tells us clearly by examing absoption/emission lines of stars and comparing to the quantum nature of various elements, also deduced through mathematics and observations of careful experimentation.

First off, density ~ Mass/Radius^3. The above discussion is confusing the physics: Stars begin their life as "fluffy" balls of gas, slowly reacting to create slightly heavier elements than the Hydrogen and Helium they begin with. This process of nuclear fusion keeps powering the star over its Main Sequence, or primary lifespan. Depending on the star's mass, it will have a proportional amount of energy during the inevitable and eventual collapse, once nuclear fusion runs out. This occurs once the mass avaliable is insufficient to continue to raise the temperature enough to promote more fusion, or if the fusion process has gone all the way to Iron - the most bound of all atomic nuclei. There can be no fusion after reaching Iron, so the pressure keeping the star from collapsing under gravity disappears, and the star collapses. When it collapses the density increases dramatically. Due to Heisenburg's Uncertainty Principle, electrons and neutrons can only be "pushed together" so much. If the density reaches a critical point, electron degeneracy pressure maintains the stars integrity, and the star becomes a white dwarf. It the white dwarf has more than 1.4 solar masses (whether at time of initial collapse or from accretion), it was collapse because the gravitational force will overcome the electron degeneracy. At this point, neutron degeneracy can take over and support the star, creating a neutron star. If the neutron star accretes mass somehow, it would collapse eventually into a blackhole. —This unsigned comment was added by 70.25.24.27 (talk • contribs) on 05:04, 23 March 2006.

Rate of rotation slow down?

The article specifies slow down rates that appear far, far too small (10-12 and 10-19 second for each century), in fact too small to logically produce the older slower-rotating stars within the universe's current age the article also mentions. Googling around, I see zebu.uoregon.edu has "about 10-15 seconds per rotation", so I suspect "per century" should be changed to "per rotation", and this would change the next sentence as follows, for a star initially rotating at 1 second: In other words, a neutron star now rotating in 1 second will rotate in 1.000003 seconds after a century, or 1.03 seconds after 1 million years. Does this look sensible? -Wikibob | Talk 22:49, 2005 Apr 19 (UTC)

This is kind of true, however generally the spin-down rate (period derivative) is expressed in dimensionless units, or if you want to think of it that way, seconds per second (=rotations per rotation). What you've said is kind of true since most observable neutron stars have rotation periods of the order of 1 second. However, on that point, both the spin period AND the period derivative are very much dependent on the type of neutron star (i.e. its history and present circumstances). So probably the whole paragraph needs to be generalised a bit, and the specific numbers and info left to the appropriate sub-articles. Rotation-powered pulsars spin down via magnetic dipole radiation, so their spin down rate depends on their magnetic field strength. The range you quoted is roughly valid for ordinary rotation powered pulsars, which have periods of mainly about 0.1-5 seconds. Recycled rotation powered pulsars otoh have periods of 1-100 milliseconds and spin down rates of 10^{-21 - -17}, while magnetars have periods around 10 seconds spin down of 10^{-12 - -10}. Accreting neutron stars OTOH vary in spin period due to the transfer of angular momentum from the accretion stream, so this can be spinning up or down and can vary with time, and have spin periods up to many 10s of seconds. All this is IMO too much detail for the top level neutron star entry (but I don't have time at the moment to improve it myself). Rkundalini 07:07, 21 Apr 2005 (UTC)

Effects of superstrong magnetic fields

The Neutron star article states:

"Another class of neutron star, known as the magnetar, exists. These have a magnetic field of above 10 gigateslas, strong enough to wipe a credit card from the distance of the Sun and strong enough to be fatal from the distance of the Moon. By comparison, Earth's natural magnetic field is 50 microteslas, and on Earth a fatal magnetic field is only a theoretical possibility; some of the strongest fields generated are actually used in medical imaging. A small neodymium based rare earth magnet has a field of about a tesla, and most media used for data storage can be erased with milliteslas."

The Magnetar article states:

"A magnetic field above 10 gigateslas is strong enough to wipe a credit card from half the distance of the Moon from the Earth1. A small neodymium based rare earth magnet has a field of about a tesla, Earth has a geomagnetic field of 30-60 microteslas, and most media used for data storage can be erased with a millitesla field.

The magnetic field of a magnetar would be lethal at a distance of up to 1000 km, by warping the atoms in living flesh2."

The two don't agree too well, though they are clearly derived from similar source material. Maybe someone who knows which version is correct can fix the incorrect one? Thanks!--Ailicec 01:18, 7 Jun 2005 (UTC)

Wouldn't the iron in your blood be affected, Xmen style, before the "atoms in living flesh" were warped? If that statment is untrue it would detract from the credibility of the 1000km statement. Rmrfstar 21:30, 19 May 2005 (UTC)

The main point being that at least one of them is wrong. ((btw, added my sig to original question, I didn't know how to do it when I wrote that) --Ailicec 01:18, 7 Jun 2005 (UTC)

Ionized electrons?

"The matter at the surface of a neutron star is composed of ordinary nuclei as well as ionized electrons." Surely the person writing this meant "ionized atoms" eg ions?

Size and mass?

Early in the article: "Neutron stars have a mass of the same order as the mass of the Sun. Their size (radius) is of order 10 km, about 70,000 times smaller than the Sun." Later in the redundant 5th paragraph: "Neutron stars are typically about 20 km in diameter, have greater than 1.4 times the mass of our Sun"

This site:1 says it's 10km

But this one:2 says it must be at least 18km

Merick June 29, 2005 15:52 (UTC)

Re: Journal Reference?

In 1933 Walter Baade and Fritz Zwicky (Phys. Rev. 45 "Supernovae and Cosmic rays") proposed the existence of the neutron star, only a year after Chadwick's discovery of the neutron. In seeking an explanation for the origin of a supernova, they proposed that the neutron star is formed in a supernova.

Should this reference be

'Remarks on Super-Novae and Cosmic Rays'
W. Baade and F. Zwicky
Phys. Rev. 46, 76-77 (1934)

The paper was in Phys.Rev. in 1934, but the discovery was still in 1933.

Keep up the good work!!!

-- JDC

Why are some pulsars?

Is it known why some neutron stars are pulsars and some aren't? Or are they all, and it just isn't observable?

Response:

If I may, there are several models of static neutron stars (non rotating) which are still used to date to model parameters, which would not be considered 'pulsars', since any received beam of radio waves wouldn't 'pulse'. I suppose the question is - will a neutron star emit the radio waves if it isn't rotating?

One of the main advantages of pulsars is that they can be detected via these pulses. Neutron stars are otherwise very small, very dark, and extremely hard to find.

-- JDC

new intro...

Concerning Fxer's new introduction, I'm ambivilant about keeping it. The new intro is less of a definition and is slower to give a clear idea of what a neutron star is and its importance (first theororized astromical object). For instance, that new sentence of the "weight" of a spoonful of a neutron star: Is that the kind of statistic we want in the intro paragraph? Also there is now presented irrelevant information on black holes and white dwarfs, which should be mentioned later... On a more positive note, the newer introduction correctly names Neutron stars as types of degenerate stars. Any other thoughts? -- Rmrfstar 00:17, 21 July 2005 (UTC)

I'd be all for a rewritten version of the intro :) It was rewritten partially, and only confused things more, so I changed it a bit to at least be factual. The statistic about the "weight" was just an eye catcher, put the most interesting info forward, and stuff people can relate to. Changing the sentence about black holes to something like "one outcome of a supernova is a neutron star", or "the supernova of a medium sized star" could be preferrable, and move the other possible outcomes to later in the body. I only started editing this page because it had no image...I hate articles without pictures, humans are visual creatures ;) --Fxer 00:37, July 21, 2005 (UTC)

Radius

Would anyone object to the radius of a neutron star being pushed down to 10km? This is the research I am doing at the moment, and literature / my results point to 10km. Cheers.

-- JDC

Recent Changes

To the person/people who continually and intentionally add errors to WikiPedia pages. Please stop. There is an entire encyclopedia out there for you to destroy. Please go to uncyclopedia or kamelopedia if you are going to ruin pages. These are here for genuine interest.

--JDC

Neutron star structure

Will some knowledgeable person please either add some references establishing the "atmosphere/crust" structural version of a neutron star, or else rewrite it to remove that wording? I'm no astrophysicist, but as a physics grad student and a follower of such things as much as I have been able in the scientific and popular literature, I have never heard of such a thing. Not saying it's false, just that we ought to have some sort of documentation.

Would a reference to the research on neutron star crusts suffice? Although almost every aspect of neutron stars is theory, we just try to make the theory better and better. The crust appears to make a dramatic difference at low central densities, where the neutron matter is below the neutron drip density, and finite nuclei are still stable. The common reference is

The Ground State of Matter at High Densities: Equation of State and Stellar Models

G. Baym, C. Pethick, P. Sutherland

Astrophysical Journal, vol. 170, p.299

since this is widely used to calculate the equation of state for the crust. You probably won't find much about crusts in the literature though. Should this go in, or is this too involved?

--JDC 00:32, 4 October 2005 (UTC)

Clarification Edit

The edit involving the 'fudge factor' is fine by me. The only observational parameters we have (to a decent degree) are mass limits. We construct models to one day test via experiments.

--JDC 23:52, 4 October 2005 (UTC)

magnetic flux of neutron stars

Can someone please tell me how neutron stars get their huge magnetic flux. I don't see how something made up of mostly neutrons can have a magnetic flux so large with an area of so small. Where exactly does the magnetic flux come from? I can't seem to find any articles or publications on this matter.

Neutron stars have high magnetic flux density. A lot of positive and negative charges in a small volume means a really dense object which implies a really dense electromagnetic field.Kmarinas86 19:45, 25 December 2005 (UTC)

Any energy is controvertible to any other form of energy. Field cancellation often leads out a detectable residual force. Color charge leads to a residual strong force which may lead to a residual electromagnetic force which leads to a residual Van der Waals force which leads the early formation of solar systems and more, and so on. I wonder what residual forces have to do with the containment of energy. —The preceding unsigned comment was added by Kmarinas86 (talk • contribs) .

My understanding is that this is best understood in terms of the same effect that allows you to build an electromagnetic pulse weapon based on explosively pumped flux compression generators: When you compact the star's core, its magnetic field doesn't go away. Instead, you're trying to stuff as much energy as was bound in the original field into the magnetic field of an object far, far smaller. As a neutron star does have free charge carriers (an electron gas on the surface and a relatively small number of protons and electrons in the interior), there isn't any physical reason preventing the star from having a magnetic field. --Christopher Thomas 21:21, 25 December 2005 (UTC)

update rotation speed

New Scientist and Physics Web report the discovery of a neutron star that rotates 716 times per second. (newscientist.com 12 january 2006)

The current "one revolution can take anything from thirty seconds to one six-hundredth of a second" could be updated to reflect this (seven-hundreth of a second) —The preceding unsigned comment was added by 212.123.21.4 (talk • contribs) on 19:34, 6 February 2006.

RRAT

New stars found called Rotating Radio Transients, or RRATs http://news.yahoo.com/s/space/20060215/sc_space/astronomersdiscoverpeekaboostars Can someone create a new article? —The preceding unsigned comment was added by 66.25.142.153 (talk • contribs) .

It would probably end up being a redirect to this article, with a section added to the neutron star page for rotating radio transients of the type described in the article. If you can provide citations to journal papers or university-hosted web sites about these stars, though, I'm sure it'll get added pretty quickly. Welcome to Wikipedia, and happy editing! --Christopher Thomas 03:09, 16 February 2006 (UTC)

Tsar Bomb

I have edited the section that says the Tsar bomb was 100 MT. The bomb (in the form tested) was only 50MT. There was a plan to make a 100MT 'dirty bomb' but this was never tested - nor created I think.

The difference between those two versions was an uranium tamper which was exchanged shortly before detonation for a lead tamper. So with all respect one can safely say that it is the biggest bomb that was 'built' by mankind, though fortunately not detonated. Knowledge about those bombs was advanced enough at the time to support the untested 100 Mt figure. Endymi0n 18:58, 20 March 2006 (UTC)