Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: trevorjohnson32 on 24/06/2017 18:07:45

Title: Do neutron stars spin? If so, why, and how fast?
Post by: trevorjohnson32 on 24/06/2017 18:07:45
has anyone ever said before that neutron stars and black holes spin at light speed or near it because all the composite neutrons are packed so tightly that there effort to spin turns the whole star? I was always told to think of it as a soup which doesn't make much sense.
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: PmbPhy on 24/06/2017 18:39:21
has anyone ever said before that neutron stars and black holes spin at light speed or near it because all the composite neutrons are packed so tightly that there effort to spin turns the whole star? I was always told to think of it as a soup which doesn't make much sense.
No neutron star as ever been found any part of which moves at near light speed. The fastest ever found moved at 24% the speed of light. The fastest spinning neutron star found yet is a pulsar 18000 light years away. Its catalogued as PSR J1748-2446ad.

And its well-known why they rotate that fast. A neutron star forms when a star collapses in on itself. All stars rotate naturally because the matter from which they were formed was originally moving and as such the resulting star has some angular momentum. As the neutron star is formed from the shrinking star the rate of spin increases in order for angular momentum to be conserved, If the star had a companion then the mass gained from stripping the star of matter also goes into increasing the angular momentum of the neutron star.

See: https://www.newscientist.com/article/dn8576-fast-spinning-neutron-star-smashes-speed-limit/
Title: Re: neutron star spin ever been eplained?
Post by: trevorjohnson32 on 24/06/2017 19:34:32
No neutron star as ever been found any part of which moves at near light speed. The fastest ever found moved at 24% the speed of light. The fastest spinning neutron star found yet is a pulsar 18000 light years away. Its catalogued as PSR J1748-2446ad.

And its well-known why they rotate that fast. A neutron star forms when a star collapses in on itself. All stars rotate naturally because the matter from which they were formed was originally moving and as such the resulting star has some angular momentum. As the neutron star is formed from the shrinking star the rate of spin increases in order for angular momentum to be conserved, If the star had a companion then the mass gained from stripping the star of matter also goes into increasing the angular momentum of the neutron star.

Has it ever been observed that protons and neutrons actually spin at all or is it just theoretical theory? because I see it says here "Unlike regular angular momentum, spin has nothing to do with actual spinning."
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: Kryptid on 24/06/2017 20:24:18
No neutron star as ever been found any part of which moves at near light speed. The fastest ever found moved at 24% the speed of light. The fastest spinning neutron star found yet is a pulsar 18000 light years away. Its catalogued as PSR J1748-2446ad.

And its well-known why they rotate that fast. A neutron star forms when a star collapses in on itself. All stars rotate naturally because the matter from which they were formed was originally moving and as such the resulting star has some angular momentum. As the neutron star is formed from the shrinking star the rate of spin increases in order for angular momentum to be conserved, If the star had a companion then the mass gained from stripping the star of matter also goes into increasing the angular momentum of the neutron star.

Has it ever been observed that protons and neutrons actually spin at all or is it just theoretical theory? because I see it says here "Unlike regular angular momentum, spin has nothing to do with actual spinning."

Neutron stars are macroscopic objects composed of microscopic particles, just like other stars are. For that reason, yes, we can indeed consider a neutron star to be spinning in the classical sense of the word. I think that individual neutrons and protons can be considered to be spinning in the sense that their internal components (quarks) are always moving. Whether quarks can be considered spinning in the classical sense, I don't know.
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: PmbPhy on 24/06/2017 20:41:56
Has it ever been observed that protons and neutrons actually spin at all or is it just theoretical theory? because I see it says here "Unlike regular angular momentum, spin has nothing to do with actual spinning."
No. Neutrons and protons cannot be considered to be spinning. Being quantum mechanical objects its not possible for a measurement of observation to be made for such spinning. E.g. the paths of their constituent quarks cannot be followed to justify such a notion. At any rate, since all protons and neutrons are identical they'd all have to have the same spin meaning it'd have to be zero. Don't confuse this with the quantum mechanical notion of spin though.
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: evan_au on 24/06/2017 23:40:53
Quote from: trevorjohnson32
has anyone ever said before that neutron stars spin ... near light speed?
A subgroup of neutron stars emit a beam of radiation that happens to pass the Earth, so we detect a "blip" every time the neutron star rotates. This allows us to measure the spin rate with great precision.
 
Adding to PmbPhy's reply, there is a class of pulsars called "millisecond pulsars" that spin faster than you can explain from the initial angular momentum of the star.

It is thought that these neutron stars have a companion star that periodically passes close enough to have some of its outer atmosphere pulled down onto the neutron star, forming an accretion disk. This adds some angular momentum from the second star's orbit onto the initial angular momentum of the neutron star.

There appears to be an upper limit at the rate a neutron star can spin; it is thought that rotating at speeds above 1500 revolutions per second would cause it to fly apart due to centrifugal force. The upcoming NICER (https://www.nasa.gov/feature/goddard/2017/new-nasa-mission-to-study-mysterious-neutron-stars-aid-in-deep-space-navigation) space telescope will study the diameter and rotation speed of pulsars.

See: https://en.wikipedia.org/wiki/Millisecond_pulsar

Quote
has anyone ever said before that black holes spin ... near light speed?
Black holes have angular momentum from the same two sources as neutron star: the angular momentum of the parent star and added via an accretion disk. It can also occur through black hole mergers.

A non-spinning black hole has a spherical shape; a spinning black hole has an equatorial bulge.

The spin of black holes has been studied using rapid X-Ray images of the light from the accretion disk; variation in the emitted light can tell astronomers about the frame dragging effects of black hole rotation.
See: https://en.wikipedia.org/wiki/Frame-dragging#Astronomical_evidence
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: chris on 25/06/2017 10:56:28
Some really nice answers here; thanks very much everyone. The discussion also put me in mind of a question that we covered on the radio a couple of weeks ago regarding the smallest particles we can detect and how to visualise them (https://www.thenakedscientists.com/articles/questions/whats-smallest-particle-we-can-detect).
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: evan_au on 25/06/2017 12:02:31
Matter spiralling into a black hole can reach velocities of 30% of the speed of light before it disappears behind the event horizon (the event horizon is the closest we can come to a "surface" of a black hole).

The study of oscillation modes in accretion disks is referred to as diskoseismology.
See: https://en.wikipedia.org/wiki/Accretion_disk
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: trevorjohnson32 on 25/06/2017 18:51:15
http://www.askamathematician.com/2011/10/q-what-is-spin-in-particle-physics-why-is-it-different-from-just-ordinary-rotation/

According to this the question is how is a magnetic field coming out of a neutron or proton. Perhaps not a magnetic field but an effect that gravity has on the energy grid lining space time. A magnetic field would be a flowing of space time, however the effect of gravity's effect on this same grid might result in something like the ionsphere similar to an electron shell, since atmosphere and ocean both depend on pressure per square inch which is caused by gravity, they should be unrelated if you were going to say that the ionsphere just sits on top of everything.
Title: Re: Do neutron stars spin? If so, why, and how fast?
Post by: PmbPhy on 25/06/2017 19:18:55
http://www.askamathematician.com/2011/10/q-what-is-spin-in-particle-physics-why-is-it-different-from-just-ordinary-rotation/

According to this the question is how is a magnetic field coming out of a neutron or proton.
I don't see that as a question. The page is saying what QM says about the phenomena, i.e. that its not possible to view the magnetic field of sub atomic particles as charge in motion. What QM is really saying is that one needs to shed the notion that all magnetic fields are generated by charge in motion, that there are really two sources of magnetism (1) charged particles in motion and (2) the intrinsic magnetic fields of sub atomic particles. Once this is accepted there are no problems left.

Perhaps not a magnetic field but an effect that gravity has on the energy grid lining space time.
You lost me. Where did gravity come into play here? Where did this notion that there's an energy grid lining spacetime come from? Energy is not a physical quantity and as such does not have a physical existence. Energy is really a bookkeeping system, i.e. a constant of motion etc.

A magnetic field would be a flowing of space time, ..
I don't see that there is any real meaning to the notion of spacetime flowing. Where did this idea come from? What is the justification for it?


Sorry but I don't understand what the rest of your post has to do with the subject.