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Neutron star flashed in the sky like a billion suns


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A neutron star forms when a massive star collapses at the end of its life. As the star dies in a supernova, protons and electrons in its core are crushed into a compressed solar mass that combines intense gravity with high-speed rotation and powerful magnetic forces, according to NASA. The result, a neutron star, is approximately 1.3 to 2.5 solar masses — one solar mass is the mass of our sun, or about 330,000 Earths — crammed into a sphere measuring just 12 miles (20 kilometers) in diameter. 

The "intense gravity" comes from the matter that has overcome electron degeneracy, right? Does a neutron star have a calculable event horizon at which point this gravity becomes "intense"?

Does the "high-speed rotation" create the "powerful magnetic forces"? I'd always thought a neutron star was inactive, a dead star, but a magnetar seems capable of quite a bit of illumination.

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Even after overcoming electron degeneracy, a neutron star is composed of ordinary matter, and there is no need for an 'event horizon', at least until the Tolman-Oppenhimer-Volkoff limit, and it becomes a Black Hole.
The 'black hole' is the event horizon.

As for the magnetic fields, other than the increase due to collapse and conservation of angular momentum ( figure skater effect ), I don't think we have a viable explanation yet.

"The origins of the strong magnetic field are as yet unclear.[31] One hypothesis is that of "flux freezing", or conservation of the original magnetic flux during the formation of the neutron star.[31] If an object has a certain magnetic flux over its surface area, and that area shrinks to a smaller area, but the magnetic flux is conserved, then the magnetic field would correspondingly increase. Likewise, a collapsing star begins with a much larger surface area than the resulting neutron star, and conservation of magnetic flux would result in a far stronger magnetic field. However, this simple explanation does not fully explain magnetic field strengths of neutron stars.[31]"

From

Neutron star - Wikipedia

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9 minutes ago, MigL said:

Even after overcoming electron degeneracy, a neutron star is composed of ordinary matter, and there is no need for an 'event horizon', at least until the Tolman-Oppenhimer-Volkoff limit, and it becomes a Black Hole.
The 'black hole' is the event horizon.

I had assumed (bad, bad!) that having 1.3 - 2.5 solar masses squeezed into a 12 mile radius sphere would generate an area where the gravity would become suddenly intense, similar to what happens when the matter overcomes neutron degeneracy as well. If one were to approach a neutron star in a space vehicle, would it feel the same gravitationally as approaching a normal star of such mass?

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14 minutes ago, Phi for All said:

I had assumed (bad, bad!) that having 1.3 - 2.5 solar masses squeezed into a 12 mile radius sphere would generate an area where the gravity would become suddenly intense, similar to what happens when the matter overcomes neutron degeneracy as well. If one were to approach a neutron star in a space vehicle, would it feel the same gravitationally as approaching a normal star of such mass?

Yes, it would be the same gravitationally. Same with the black hole, too.

Edited by Genady
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1 minute ago, Genady said:

Yes, it would be the same gravitationally. Same with the black hole, too.

But with the black hole, the EH represents an area where gravity curves spacetime intensely. I was wondering if, approaching a neutron star, there would be a similar but less intense curvature. I remember Larry Niven's fictional life on a neutron star, and dealing with a surface gravity billions of times stronger than Earth, but I can't remember if he wrote about any Earthlings trying to approach it.

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1 minute ago, Phi for All said:

But with the black hole, the EH represents an area where gravity curves spacetime intensely. I was wondering if, approaching a neutron star, there would be a similar but less intense curvature. I remember Larry Niven's fictional life on a neutron star, and dealing with a surface gravity billions of times stronger than Earth, but I can't remember if he wrote about any Earthlings trying to approach it.

This is correct. Approaching a neutron star, there would be a similar but less intense curvature. Moreover, approaching any star (or anything else for that matter) there is a similar, but much less intense curvature. The gravity in empty space around any radially symmetric mass has the same shape and only differs in intensity.

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2 hours ago, Phi for All said:

But with the black hole, the EH represents an area where gravity curves spacetime intensely. I was wondering if, approaching a neutron star, there would be a similar but less intense curvature. I remember Larry Niven's fictional life on a neutron star, and dealing with a surface gravity billions of times stronger than Earth, but I can't remember if he wrote about any Earthlings trying to approach it.

I read that as similar to asking what is the minimum most  stable orbital distance, something can orbit a BH? Which would be actually the photon sphere at 1.5 Schwarzchild radius.

Where would that be for a Neutron star, (as opposed to Magnetar and Pulsar)

Edited by beecee
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2 hours ago, beecee said:

I read that as similar to asking what is the minimum most  stable orbital distance, something can orbit a BH? Which would be actually the photon sphere at 1.5 Schwarzchild radius.

Where would that be for a Neutron star, (as opposed to Magnetar and Pulsar)

The maximum mass for a neutron is star is ~2.17 solar masses, and one that massive would have a radius of ~15 km.

The event horizon for a BH with that mass is ~6.43 km, and has a photon sphere at ~9.65 km.    At the surface of the Neutron star, escape velocity would be ~ 0.463 c and orbital velocity would be ~0.33 c, both well short of c.

 

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