Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/01/2008 17:10:31
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Dear All (ie: Ian [:)])
Magentars are neutron stars with magentic fields so big that they are up to (get this) one thousand trillion times the Earths magnetic field !!
Here's one...
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Artists Impression !!
What I'd like to know is what had stopped these things from becoming Black Holes ?..especially when they apparently are formed from stars big enough to do the Black Hole deed !!
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They are probably rotating too fast. The law of conservation on angular momentum means that if a thing is rotating and it collapses it rotates faster like skaters pulling in their arms and doing a superfast pirouette. Now things can't go round faster than the speed of light and if they've got too much angular momentum stars just can't collapse into a black hole.
A rotating black hole (Kerr black hole QV) has an upper limit to the angular momentum that it may possess.
Angular momentum conservation is one of the reason why it is in fact quite difficult to make or fall into a black hole.
The other reason is trapped magnetic field because that also gets stronger as the body collapses and also tends to prevent collapse. It has recently been suggested that magnetic fields which have been largely ignored when considering how large objects evolve in the universe may have much more effect than first thought.
The gravitomagnetic effects probably only come to play significantly once something has collapsed into a black hole and I have yet to find any analysis of the effects they have on a rapidly rotating collapsing mass.
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I thought Magnetar was 1 of the X-men [:(]
I'm, puzzled - but I dare say Ian can enlighten me. Neutron stars are made of neutrons, which have neutral charge. How can something without charge have a magnetic field? [???]
Am I misguided about the connection between magnetism & electrical charge?
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The sun and the earth are essentially electrically neutral objects but both possess significant magnetic fields many of the major activities on the sun like spots and prominaces are electromagnetic in origin.
The sun is made out of plasma which although on the whole electrostatically neutral the electrons and the nuclei are all moving about independently the electons and the nuclei have very different masses and so in turbulent conditions tend to move differently and this will create in effect electrical currents flowing and therefore generate magnetic fields.
The earth's magnetic field is believed to originate from motions within its conducting iron core. This is nothing to do with iron being a ferromagnetic material when cool because the core is well above the temperature that allows this to happen. The motion of electrons and atoms in the earth's magnetosphere also generates magnetic fields and this is one of the reasons why it varies a bit in the short term.
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I'm, puzzled - but I dare say Ian can enlighten me. Neutron stars are made of neutrons, which have neutral charge.
They're mostly made of neutrons, but there must be some charged particles in the mix in order to generate magnetic fields, as you say. There are various predictions for what might exist alongside neutrons in the neutron star, but no one's made observations of the core of such a star yet.
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[^] (smug grin)
Thank you both for your informed replies.
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The magnetic fields of magnetars are probably residual magnetic fields from the originating stars compressed as the stars collapsed neutron stars are also believed to be superconducting
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Thank you for a fascinating thread.