Millimeter-tall mountains on neutron stars

[notFritzArgelander]

https://phys.org/news/2021-07-bug-life- ... utron.html

When I was in grad school we already knew that neutron stars would have very short mountains, so there is little new here.

[GCoyote]

What keeps these "mountains" from immediately spreading out evenly over the surface of the neutron star? The strong nuclear force?

[notFritzArgelander]

What keeps these "mountains" from immediately spreading out evenly over the surface of the neutron star? The strong nuclear force?

Actually it's solid state forces due to electromagnetism, the same force by which Earth's mountains resist tidal deformation. The top surface layer is likely iron nuclei in a crystalline structure, the neutronized layer is deeper into the star.

[GCoyote]

What keeps these "mountains" from immediately spreading out evenly over the surface of the neutron star? The strong nuclear force?

Actually it's solid state forces due to electromagnetism, the same force by which Earth's mountains resist tidal deformation. The top surface layer is likely iron nuclei in a crystalline structure, the neutronized layer is deeper into the star.

Thanks, I did not realize any nuclear species survived the process of neutron star formation.

[notFritzArgelander]

What keeps these "mountains" from immediately spreading out evenly over the surface of the neutron star? The strong nuclear force?

Actually it's solid state forces due to electromagnetism, the same force by which Earth's mountains resist tidal deformation. The top surface layer is likely iron nuclei in a crystalline structure, the neutronized layer is deeper into the star.

Thanks, I did not realize any nuclear species survived the process of neutron star formation.

The top of the crust is iron 56 and as you go deeper you get heavier "magic number" nuclei that are increasingly neutron rich. Then there is a phase where the nuclei start to touch making a swiss cheese phase maybe. There is a sea of free fluid neutrons. Finally the nuclei dissolve as the pressure increases. That's the old picture. About 7 years ago the inner crust was calculated to need revised scenarios.

https://physics.aps.org/articles/v7/30

But the outer crust old view remains unchanged.

[GCoyote]

"Eventually, in the inner crust, the nuclei cannot accept any more neutrons, and free neutrons form a superfluid that permeates the lattice."

Okay, now I'm thinking that if you have nuclei containing protons, you must have electrons, I assume these are unbound because of the temperatures. Do we know what mischief they are up to?

[notFritzArgelander]

"Eventually, in the inner crust, the nuclei cannot accept any more neutrons, and free neutrons form a superfluid that permeates the lattice."

Okay, now I'm thing that if you have nuclei containing protons, you must have electrons, I assume these are unbound because of the temperatures. Do we know what mischief they are up to?

Well… most of the calculations are done for T=0 but even at relatively high temperature of formation the electrons are degenerate since the Fermi energy is larger than the temperature.

[GCoyote]

I had to look up Fermi Energy but that does make sense.

Thanks again!

[Michael131313]

Thanks for the post nFA. Both links were very interesting.