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View Full Version : Bizarre neutron star is old before its time



ToSeek
2006-Jul-06, 06:51 PM
Bizarre neutron star is old before its time (http://www.newscientistspace.com/article/dn9495-bizarre-neutron-star-is-old-before-its-time.html)


Despite its youth, De Luca's team found that the star is moving like an old fogy. The star shows a periodic brightening at X-ray wavelengths, suggesting it is rotating just once every 6.7 hours. It would normally take a neutron star millions of years to slow down that much.

Jerry
2006-Jul-10, 06:14 PM
I don't see why this would challenge theory - any more than any other neutron star. Is there a reason to suppose that all neutron stars start with very tight orbital rotations?

This neutron star is fairly close - if there is selecton bias in the identification of neutron stars, there may be many of these objects just below the radar.

BigDon
2006-Jul-10, 11:41 PM
Is there a reason to suppose that all neutron stars start with very tight orbital rotations?

As I understand it all neutron stars rotate rapidly due to conservation of momemtum from there creation. (The old spinning ice skater analogy comes to mind. They spin faster when they pull their arms in close to their bodies.)

loglo
2006-Jul-11, 12:24 AM
Is there a reason to suppose that all neutron stars start with very tight orbital rotations?

Given the conventional theory that stars spin up as they collapse due to conservation of angular momentum, any young NS with a slow rotation would either have experienced a large amount of braking, been subsequently spun up by a companion star or have started from a negligably spinning star originally.

The article says that they can show that a companion hasn't spun it up as the magnetic fields are too strong and would interfere with the process. So either there is a braking mechanism they don't know about or it came from a star with a very slow intial rotation. The latter seems unlikely since stars are spun up through their initial collapse themselves. Hence the conumdrum I guess.

A back of the envelope calculation:- 2000 years with a slowdown rate of a comparably old NS like the Crab of about 10^-13 sec/sec gives around .00026 seconds of change in the rotation rate which in theory generally starts in the millisecond range. So the detected rotation is about five or six magnitudes too low for the theory.

*edit - change large to low in final line.