Why do neutron stars have magnetic fields?

[llivinglarge]

My astronomy professor was stumped when a student asked the question during a lecture today on stellar remnants.

 

[michaelmozina]

http://www.hypography.com/article.cfm?id=34300<br />http://www.astro.umd.edu/~miller/nstar.html<br /><br />The first link explains the theory of how the magnetic field is formed, and the second link explains some of the theory behind the makeup of the "shell" of a neutron star which tends to be made up of predominantly iron nuclei, stripped of their electrons. Keep in mind that most neutrons stars "spin" to some degree, some of these even "tumble" it seems.<br /><br />http://www.spaceref.com/news/viewpr.html?pid=19626<br /><br />One can imagine that the inherent spin has something to do with the alignment and the arrangement of these magnetic fields. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[why06]

I answer you because I asked that question my self once and got a strange a vague answer. In truth I do not know what causes it. It is electric force that keeps our planet from caving in. maybe the electrons are still moving deep inside the star keeping it from becoming a blackhole. If I were you I would look into <font color="yellow">pulsars<font color="white"><br /><br /><br />If you find out how post it. Like I said nobody really knows....</font></font> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[yevaud]

A Pulsar *is* a Neutron star, FYI. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[mlorrey]

One thing to keep in mind is that the electric force is a separate nuclear force from the magnetic force. While the neutron lacks electric charge, there is nothing that says it cannot hold a magnetic field.<br /><br />Earth has what is called an "electromagnetic field" because it is a magnetic field generated by electric currents in the mantle and core, and any magnetic field can induce electric currents in conductors quite easily.<br /><br />As Michael said, neutron stars typically have a crust of regular matter, typically mostly iron, since that is the element that takes the most net energy to compress into neutrons. As the neutron star spins, there are both thermal compressive forces on the iron shell, with a hot inner surface due to extreme gravity, and a cooler outer surface due to radiation to space, with significant electric currents and magnetic fields generated from this thermal gradient. There are also coriolis forces from the spin of the neutron star, and given the high spin rates, they are rather severe coriolis forces that also will generate electric currents and thus induce magnetic fields. <br /><br />The neutronium of the actual neutron star, however, acts, theoretically at least, like a Bose Einstein Condensate: it should hold and conduct an induced magnetic field produced by its iron crust, even though its 100% neutron makeup makes it impervious to electric conduction.

 

[michaelmozina]

http://www.spaceref.com/news/viewpr.html?pid=19685<br /><br />There was a pretty good article today about the a siesmic technique that was used to measure the depth of a"crust" of one neutron star. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[CalliArcale]

Cool article! Thanks for sharing! <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[why06]

First of all Yevaud I know that...I meant a pulsar releases a large amount of gamma rays at its poles and that wopuld be good to study. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[yevaud]

Ah. Point duly noted. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[why06]

sorry wasn't able to finish that last post that, but yes pulsars and nuetron are the same, but htis brings up a question.<br /><br />Q1: If a nuetrons half life is so small without a proton to connect to it-How could a nuetron tar possibly exist for so long.<br /><br />Q2: -sorry, guess I should have said "questions"- Anyway what I was trying to say is that is that: If the nuetrons in nuetron stars decompose would that not give off proton and electrons and there fore a magnetic field.<br /><br />Q3: We know a nuetron is a mix between a electron and proton...so woul a nuetron generate a magnetic field by simply being in this contant state. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[smartnova]

there is an interesting discussion on this subject at Space KB . and more on magnetic fields in neutron stars. They discuss different theories.

 

[michaelmozina]

I very much like the explanation of using the inherent spin of the neutron crust to explain the magnetic field. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[severian]

Hmm, this isn't directly related to the basic question, but it might serve to answer somewhat.<br /><br />As has previously been pointed out, electric field is not the same thing as magnetic field, and whilst electrical fields require a point charge on which to originate, magnetic fields do not (in fact, _almost_ by definition they do not originate on a point).<br /><br />The reason that neutron stars have such strong magnetic fields (ie, magnetar's and pulsar's are two well known examples of this), is that much like angular momentum (which causes the fast spin of a neutron star), magnetic field (or flux contained, to be more accurate) is a conserved quantity. This means that as the radius of a star shrinks (goes supernova), its magnetic field increases.<br /><br />The actual factor is actually squared, so with every halving of radius, the magnetic field increases four fold. This results in the massive magnetic fields of neutron stars (they are the more magnetic objects in the Universe).

 

[why06]

Cool I did not know that about supernovas and I never thoght of a magnetic field as not flowing to a source, but now that I think about it it makes perfect sense that all those things are true. Unfortunately this still does not answer the main question<br /><br />-Thanks for the info. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[why06]

I guess the truth is all and all we don't know- No one knows yet- I bet even Steven Hawking would be hard pressed to answer that one.<br /><br />-In truth more research need to be done and questions answered. Then, who knows, you may turn out to be the first physics teacher to be able to look one of your own students in the eye, if you ever become a teacher, and deliver a solid answer when he asks you the same question. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>