What is the composition of the crust and atmosphere on a neutron star?

In summary: The surface gravity on a neutron star is about 10^11 times Earth's, and the magnetic field is about 10^12 gauss. These intense fields cause atomic structure to change, leading to the presence of elements near the core that are not found on the surface.
  • #1
Jimmy Snyder
1,127
20
There aren't any electrons on a neutron star right? They all get squooshed into the protons to make the neutrons. Am I right about that?
 
Astronomy news on Phys.org
  • #2
http://www.astro.umd.edu/~miller/nstar.html

Anyway, imagine starting at the surface of a neutron star and burrowing your way down. The surface gravity is about 10^11 times Earth's, and the magnetic field is about 10^12 Gauss, which is enough to completely mess up atomic structure: for example, the ground state binding energy of hydrogen rises to 160 eV in a 10^12 Gauss field, versus 13.6 eV in no field. In the atmosphere and upper crust, you have lots of nuclei, so it isn't primarily neutrons yet. At the top of the crust, the nuclei are mostly iron 56 and lighter elements, but deeper down the pressure is high enough that the equilibrium atomic weights rise, so you might find Z=40, A=120 elements eventually. At densities of 10^6 g/cm^3 the electrons become degenerate, meaning that electrical and thermal conductivities are huge because the electrons can travel great distances before interacting.

Deeper yet, at a density around 4x10^11 g/cm^3, you reach the "neutron drip" layer. At this layer, it becomes energetically favorable for neutrons to float out of the nuclei and move freely around, so the neutrons "drip" out. Even further down, you mainly have free neutrons, with a 5%-10% sprinkling of protons and electrons.
 
  • #3
Thanks Bobbywhy. Your answer is far more interesting than I had figured on. What prompted my question was this quote from the book "QFT III: Gauge Theory" by Eberhard Zeidler, page 950.

Eberhard Zeidler said:
fermions of the same type (e.g., the electrons in a neutron star) are governed by the Fermi-Dirac statistics

If it were me, I would have said electrons in an atom.
 
  • #4
It is indeed interesting. Beyond the neutron drip density, neutrons tend to clump together. This is analogous to the reason why a water drop likes forming a sphere. So we get bubbles of neutrons floating in otherwise neutron-rich nuclei. As we go deeper we encounter other phases, what are sometimes called "nuclear pasta," before getting to the regime where neutrons dominate. Near the core, there will be more than 10 neutrons for every proton.

http://relativity.livingreviews.org/Articles/lrr-2008-10/

Section 3.3 describes this series of phase transitions and has some pretty pictures.
 
Last edited by a moderator:
  • #5
Jimmy Snyder said:
There aren't any electrons on a neutron star right? They all get squooshed into the protons to make the neutrons. Am I right about that?

According to most sources, it appears that neutron stars have a crust of electron degenerate iron about 1km thick (with an outer & inner crust) and a plasma atmosphere.

A couple of sources-
http://arxiv.org/abs/0705.2708v2
http://var.astro.cz/brno/perseus4_2002_clanek2.pdf
 

1. What are electrons on a neutron star?

Electrons on a neutron star are subatomic particles that have a negative charge and are responsible for the flow of electricity and the formation of chemical bonds.

2. How are electrons affected by extreme conditions on a neutron star?

Due to the intense gravitational and magnetic fields on a neutron star, electrons experience extreme pressure and are squeezed together, resulting in a much higher density compared to electrons on Earth.

3. How do electrons contribute to the properties of a neutron star?

The high density of electrons on a neutron star contributes to its overall mass and magnetic field. Additionally, the flow of electrons is responsible for the generation of radiation and the formation of the star's atmosphere.

4. Can electrons escape a neutron star?

Despite their high density and intense pressure, some electrons on a neutron star can escape into space due to the strong magnetic fields. These escaped electrons can form a surrounding nebula, also known as a "pulsar wind nebula".

5. How do electrons on a neutron star impact our understanding of the universe?

The study of electrons on a neutron star provides valuable insights into the extreme conditions and physical processes that occur in the universe. They also play a crucial role in the formation and evolution of neutron stars, which are some of the most fascinating and mysterious objects in our universe.

Similar threads

  • Astronomy and Astrophysics
2
Replies
48
Views
905
  • Astronomy and Astrophysics
Replies
10
Views
1K
  • Astronomy and Astrophysics
Replies
10
Views
2K
  • Astronomy and Astrophysics
Replies
2
Views
2K
  • Astronomy and Astrophysics
Replies
5
Views
4K
  • Astronomy and Astrophysics
Replies
6
Views
2K
Replies
8
Views
1K
  • Astronomy and Astrophysics
Replies
4
Views
1K
  • Astronomy and Astrophysics
Replies
7
Views
2K
Replies
6
Views
2K
Back
Top