Discussion: Biggest Stars Make the Biggest ...

[Fraser]

SUMMARY: Astronomers from the Harvard-Smithsonian Center for Astrophysics have found evidence that the big stars become extremely powerful magnets when they die. They used the Australia Telescope Compact Array and Parkes radio telescope in eastern Australia to watch a powerful magnetar - an exotic neutron star with a magnetic field one quadrillion times more powerful than the Earth's field, which releases X-rays and gamma radiation. They found clues in the surrounding nebula that indicate that the magnetar used to be a star with 30-40 times the mass of the Sun. Larger stars spin faster when they become neutron stars (500-1000 times a second), and this generates a powerful dynamo that boosts the magnetic field.

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[John L]

Could Magnetars be partial quark stars? I can picture a quark core rotating at one speed and a neutron mantel/crust spinning at a different rate creating the intense magnetic fields of the magnetar.

[antoniseb]

It's interesting that there are several factors that determine the final state of a large star, and that mass alone does not seem to be the soul determinant.

It was amusing, reading about how if there was a magnetar as far away as the moon that all our credit card's magnetic strips would be wiped. If there were a magnetar there, who'd be around to care?

[StarLab]

Would charge and spin also affect magnetar configuration?

[Duane]

Originally posted by John L@Jan 28 2005, 10:22 AM
Could Magnetars be partial quark stars? I can picture a quark core rotating at one speed and a neutron mantel/crust spinning at a different rate creating the intense magnetic fields of the magnetar.

Yes, they would be partially quark and other exotic matter, at least according to the most recent Equations of State calculations. I haven't seen anything discussing a different spin rate between the crust and the interior, but what an interesting idea.

I have seen some studies and discussion regarding the solar and earthly magnetic fields arising from differencial rotation between the inner core and the outer layers but I never made the leap to assign such an effect to a neutron star/magnetar.

I must spend some time to look around.

[gnosys]

A couple of very elementary, perhaps silly questions which perhaps someone might answer:

1. What determines how fast a neutron star or anything else rotates? What supplies the energy?

2. Can objects rotate on more than one axis? I can take a basketball spinning on a vertical axis and then start rotating its poles around a new horizontal axis... but it seems to me that all points on the surface of the ball will now move in concentric circles oriented between an apparent single new pair of poles. Does that mean there can really be only one true axis of rotation? (Like I said, this is elementary stuff. Sorry.)

3. I've recently read about "frame-dragging," whereby spacetime is distorted by the spinning of a black hole. Using the familiar illustration of a sheet of rubber being warped around a representation of a planet to show how the gravity of a non-rotating object curves spacetime, can this further "frame-dragging" effect be represented simply by twisting the already warped rubber sheet at the point where the rotating body is located? (Sidebar question: Presumably the rubber sheet in any such illustration of gravity is only depicting two of the four dimensions. Would there be any difference in how this illustration looks depending on whether we're omitting one spatial dimension and time or two spatial dimensions?)

4. A totally different matter: I've read that space becomes time-like at the event horizon of a black hole,since the future lies inevitably in the direction of the black hole. Does time likewise somehow become space-like? What would that mean? Since the Big Bang seems to be analogous to a "white hole," was time space-like at the "moment" of the Big Bang? If so, does that in and of itself totally remove any lingering questions or problems related to the concept of "before" the Big Bang?

Perhaps the Arrow of Time is related to Dimension #4 even "now" being in a state of transformation. I've always liked the term "the unfolding moment" as a description of what is happening with the universe. It's not that difficult to understand that every point in the universe is the point of the Big Bang; you can't travel in space to the point of the Big Bang, because the point of the Big Bang has expanded to become the whole universe. What's hard to conceive of is that the moment of the Big Bang is expanding into all the moments of the history of the universe, including this one. Or is that misleading? There are black hole singularities existing at this very moment, but we are fortunately removed from them by spatial distance... and it's only when you get right up next to them that spatial distance starts looking time-like. Presumably there is NO spatial distance separating us from the point of the Big Bang. Time, however, DOES separate us from the moment of the Big Bang. If the point of the Big Bang expanded to become all the space in the universe, including here, AND the moment of the Big Bang expanded to become all the time in the history of the universe, including now... then there would be no separation between us and the Big Bang. Here and now would be indistinguishable from the point and moment of the Big Bang. Time, then, is probably time-like because it's the one dimension which gives us any separation from the Big Bang.

Another way to look at it: if we think of the Big Bang as a "white hole," we could think of the universe (and ourselves, of course) as being in a state of free fall away from the Big Bang -- plummeting inevitably into the future in very much the same way as things plummet inevitably into a black hole once it catches them. If the expansion of the universe starts to slow down, does that in one sense reflect the gradually diminishing "push" of the Big Bang/white hole/singularity?

Whoops, got off on a tangent. I'm serious about the first couple of questions, though.

[wstevenbrown]

I am shocked... shocked to find that there is dynamo action going on here!

Gnosys-- The pseudorandom swirling of large masses of gas resolves itself into a rotation of the compacted body (star) thru the conservation of angular momentum-- all of the momentum arrows of all of the particles added together should equal the angular momentum of the compacted body. This is an appropriate use of the 'skater-pulling-in-her-arms' model.

All rotations of a three-dimensional body can be 'simplified' to a two-axis rotation by transformation of coordinate axes.

Oops-- must run! S