View Full Version : Episode 42: Magnetism Everywhere

2007-Jun-25, 03:00 PM
You probably don't realise it, but magnetic fields are everywhere. We're not talking about the magnets in your speakers, your electronic equipment or on the fridge door. We're talking about the gigantic magnetic fields that surround planets, stars, galaxies and some of the most exotic objects in the Universe.<br />&nbsp;<br />

<strong><a href="http://media.libsyn.com/media/astronomycast/AstroCast-070625.mp3">Episode 42: Magnetism Everywhere (13.5MB)</a></strong><br />&nbsp;<br />

Read the full blog entry (http://www.astronomycast.com/physics/episode-42-magnetism-everywhere/)

2007-Jun-30, 04:32 AM
OK. Magnetism is generated by an electrical current. A Magnetar is a neutron star presumably rotating very quickly. A neutron star is a star so dense that the electron degeneracy is overcome (essentially all of the electrons merge with the protons).

So there are no electrons or protons in a Magnetar. Where in the world does the magnetic field come from?

Himanshu Raj
2007-Jun-30, 12:50 PM
That's an interesting question. I searched wikipedia (http://en.wikipedia.org/wiki/Magnetar) for that and found the answer. The existence of the magnetic feild seems to hidden in the formation of the magnetar. Still its all fuzzy inside my head.

I would like to extend the question to include Black Holes. Black Holes have degenerate matter of infinite density. Not regular matter of electron (that gives the characteristic of magnetic feild) and protons. They too have magnetic field (http://www.astro.ku.dk/~boris/RelViz/). Where the magnetic field here come from?

2007-Jul-02, 06:44 AM
Part of this makes sense and part of it makes no sense. The Wikipedia article seems to say that convection within the collapsing neutron star creates the magnetic field through the dynamo effect. The problem is that the dynamo effect (which relies on electrical current flow) can't work with all neutrons, right?

Well, the last part of the sequence makes some kind of sense. It hints that the neutron star itself doesn't actually preserve the magnetic field. That is done by a plasma of mostly iron that forms a shell around the magnetar for the first 10,000 years or so. Presumably (my presumption, not the article's), when the rotation slows, the plasma collapses onto the magnetar and the magnetic field goes away (since the plasma becomes neutrons).

I think...

I'm still unclear on exactly how this all works. Parts of it almost seem to work out but there are still large holes in my mind.

Himanshu Raj
2007-Jul-02, 03:21 PM
Magnetohydrodynamics. Thats what Pamela pointed out.

2007-Jul-05, 06:46 PM
:-( I've downloaded the show twice, but every time I play it, it stops at about a minute and a half.

2007-Jul-05, 07:55 PM
:-( I've downloaded the show twice, but every time I play it, it stops at about a minute and a half.

Chigh, it sounds like there's an issue with the download and you're not getting the full file. Are you downloading manually, or are you using an aggregator?

If you're downloading the show manually, try deleting your chache and trying again (see here (http://kb.iu.edu/data/ahic.html)). When you've downloaded the show, it should be 13.48MB (on Windows, right click on the file and choose "properties" - the file size is on the tab "general").

Let us know if this helps - and feel free to drop us an email to info(at)astronomycast(dot)com

Astronomy Cast
Web Assistant

2007-Jul-06, 05:16 AM
Magnetohydrodynamics. Thats what Pamela pointed out.

That still only works if you have electrons to generate the current. The current and magnetic field are related. So far as I know, no current, no magnetic field. I can believe that the neutrons can operate as a fluid (metals under enough pressure can operate as fluids as well), but that still doesn't help generate a current with no electrons to work with.

Now, if we somehow were to generate the magnetic field in the plasma surrounding the star as it collapsed, maybe that would work. Perhaps something exotic like frame dragging comes into play as well with something that dense spinning that fast.