Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Alan McDougall on 18/08/2008 01:48:05
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Greetings,
Neutron pulse stars are believed to rotate at almost the speed of light, making them the most accurate time clocks known.
My problem, given the enormous density of these objects and colossal gravity forces trying to rip them apart or turn them into a black hole, what are the possible fates of such objects? The “centrifugal force” of such an object must also be unimaginable huge, somehow causing a balancing act between the pulse star "shrinking into black hole" or remaining a "colossally dense dark object" by the outward force of the immense centrifugal force.
Regards
Alan
NASA ARTICLE
Pulsars were first discovered in late 1967 by graduate student Jocelyn Bell Burnell as radio sources that blink on and off at a constant frequency. Now we observe the brightest ones at almost every wavelength of light. Pulsars are spinning neutron stars that have jets of particles moving almost at the speed of light streaming out above their magnetic poles.
These jets produce very powerful beams of light. For a similar reason that "true north" and "magnetic north" are different on Earth, the magnetic and rotational axes of a pulsar are also misaligned.
Therefore, the beams of light from the jets sweep around as the pulsar rotates, just as the spotlight in a lighthouse does. Like a ship in the ocean that sees only regular flashes of light, we see pulsars turn on and off as the beam sweeps over the Earth. Neutron stars for which we see such pulses are called "pulsars", or sometimes "spin-powered pulsars," indicating that the source of energy is the rotation of the neutron star
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A star has to be above the Chandrasekhar limit of 1.44 solar masses to form a neutron star. Above 2 or 3 solar masses the star will collapse to a black hole. Between these two mass values, any rotation of such a star slows with time (and this is measurable) and will ultimately just become a ball of neutrons. I would expect it still to accrete mass however, because of its strong gravitational field but I don't know whether such an object has been observed. I expect it would behave much as a black hole does, if a little less dramatically.
Late edit because I said magnetic and meant gravitational.
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Neutron pulse stars are believed to rotate at almost the speed of light, making them the most accurate time clocks known.
Do you mean that the peripheral speed is high?
I'm not sure about the 'most accurate time clock' idea, although they may well be regular in the short term. As their angular momentum will not change, their radius may well change, their angular velocity would be expected to change as a result.
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Rotating at the speed of light doesn't make sense, I'm afraid. The speed of light is a linear measurement, not a rotational one. An important thing to remember is that the pulse period is not the same as the pulse rate, which is the rate of rotation of the pulsar - the fastest spinning pulsar is PSR J1748-2446ad, which spins 716 times a second, while it's pulse period is 0.00139595482 seconds.
Rotating at just 716 rps, the surface of this pulsar will be traveling at well below relativistic speeds and while the centripetal forces will be high they won't be sufficient for the pulsar to fly apart.
The rate of rotation of pulsars can be very stable and rival that of atomic clocks, but many of them show variations, either due to in-falling matter, or through internal 'star-quakes' as the interior reacts to/relieves internal stresses.
Neutron stars are not thought to be totally smooth and featureless but to have distinct terrains and landscapes, with surface features up to a couple of centimeters high.
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I stared that some pulstars rotate at "ear light speed", not at the speed of light. Thus causing a huge comflict between the inward gravitational force and the immense outward centrifugal force trying to rip the star apart
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How near is 'near'?
I suggest that LeeE is right in suggesting that peripheral speeds of even a fraction of c would not be possible.
Where did you get your info? Was the source reputable?
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I stared that some pulstars rotate at "ear light speed", not at the speed of light
Ah - that's probably why I misinterpreted it then.
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Just a little supplemental question to this thread:
Neutrons consist of quarks bound by the strong force. Unlike other forces, the strong force gets stronger with distance. If neutrons are densely packed, as in a neutron star, would the strong force from any given neutron affect the quarks in a neighbouring neutron? In other words, does the strong force, as well as gravity, serve to hold a neutron star together?
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I'm not really up on QM but the strong force strikes me more like a specific link between specific quarks and/or gluons rather than an indiscriminate force, which acts upon all quarks/gluons within range.
If it's a specific link then it wouldn't help hold the neutron star together but if it was indiscriminate it plausibly could.