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20
votes
7answers
4k views

Why do neutrons repel each other?

I can understand why 2 protons will repel each other, because they're both positive. But there isn't a neutral charge is there? So why do neutrons repel? (Do they, or have I been misinformed?) The ...
27
votes
6answers
7k views

How come neutrons in a nucleus don't decay?

I know outside a nucleus, neutrons are unstable and they have half life of about 15 minutes. But when they are together with protons inside the nucleus, they are stable. How does that happen? I got ...
46
votes
9answers
3k views

Do all black holes have a singularity?

If a large star goes supernova, but not enough mass collapses to form a black hole, it often forms a neutron star. My understanding is that this is the densest object that can exist because of the ...
6
votes
3answers
639 views

What allows the modified Urca process to work at lower density than direct Urca in neutron star cooling?

The dominant method of neutron star cooling is neutrino emission. There are two regimes usually presented, the "direct Urca" and "modified Urca" processes, each of which are sequences of neutron decay ...
4
votes
2answers
1k views

What would happen to a teaspoon of neutron star material if released on Earth?

I've read on NASA's page on neutron star that one teaspoonful of that star would weigh over 20 billion tonnes on Earth. If it was somehow possible to bring it to earth would it: Burn and disappear ...
22
votes
5answers
3k views

Can there be Electron and/or Proton Stars?

What happens to all of the electrons and protons in the material of a neutron star? Could there ever be an electron star or a proton star?
8
votes
4answers
760 views

Do neutron stars reflect light?

The setup is very simple: you have a regular ($1.35$ to $2$ solar masses) evolved neutron star, and you shine plane electromagnetic waves on it with given $\lambda$. Very roughly, what shall be the ...
3
votes
2answers
156 views

Smolin on Cosmological selection and neutron stars

Regarding the cosmological selection hypothesis and testable predictions, Lee Smolin asserted the following: "Smolin: I did make two predictions which were eminently checkable by astrophysical ...
19
votes
3answers
2k views

What stabilizes neutrons against beta decay in a neutron star?

Free neutrons are known to undergo beta decay with a half-life of slightly above 10 minutes. Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of ...
15
votes
4answers
576 views

Are Neutron stars transparent?

Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
2
votes
2answers
124 views

Neutron star: free fall acceleration

The textbook from which I teach physics at the end of secondary school, has a question about a neutron star: $M_{star}=1.4\cdot M_{sun}$, radius 15km. "Calculate the free fall acceleration at the ...
3
votes
2answers
315 views

Are there any known neutron stars just below the Tolman–Oppenheimer–Volkoff limit?

Do we know any neutron stars just below the Tolman–Oppenheimer–Volkoff limit? And how are they different from most other neutron stars?
2
votes
1answer
154 views

What is the pressure at the center of the Earth? (Or a neutron star)

The center of the Earth has microgravity and is thought to be solid and almost 6000 degrees hot. What is the pressure like there? The confusing thing, for the common man I suppose, is that there's no ...
13
votes
1answer
1k views

What is the theoretical lower mass limit for a gravitationally stable neutron star?

I ask here intentionally not for the size of the smallest possible observed size of neutron stars, which corresponds approximately to the well-known Chandrasekhar-limit for the upper limit of the ...
12
votes
3answers
401 views

How does the Pauli exclusion principle create a force in degenerate matter?

My understanding is that when it comes to forming a white dwarf, it is the electron degeneracy pressure, due to the Pauli Exclusion Principle, preventing collapse in of the white dwarf. If the ...
15
votes
1answer
2k views

Turned to steel in the great magnetic field

This is obviously a "fun" question, but I'm sure it still has valid physics in it, so bear with me. How great of a magnetic field would you need to transmute other elements into iron/nickel, if ...
14
votes
3answers
570 views

How would neutron matter appear to the naked eye?

Neutron matter is matter comprised entirely of neutrons, as it exists in neutron stars. Most optical phenomena encountered in everyday life, such as light reflection and spectral absorption (i.e. ...
11
votes
1answer
349 views

Introduction to neutron star physics

I enjoy thinking about theoretical astrophysics because I want to understand black holes. Given that no one understands black holes, I like to ponder the nearest thing to a black hole: a neutron star! ...
4
votes
2answers
401 views

What is the temperature of the surface and core of a neutron star formed 12 billion years ago now equal to?

In what part of the spectrum is it radiating? In the infrared, in the microwave? Or is not radiating anymore at all? In russian: Чему сейчас равна температура поверхности и ядра нейтронной звезды, ...
6
votes
1answer
190 views

Upper Mass Limit of Quark Stars

While there is no confirmation that quark stars exist, is there any theoretical limit analogous to (but different from) the Tolman–Oppenheimer–Volkoff limit for neutron stars? In other words, what is ...
3
votes
1answer
372 views

neutrinos by formation of “neutron pairs”

Here : http://www.newscientist.com/article/dn20084-neutron-star-seen-forming-exotic-new-state-of-matter.html are news on superfluidity in a neutron star. The necessary bosons they say are pairs of ...
10
votes
2answers
1k views

Black Hole Photon Sphere

The photon sphere is a spherical region in space where photons are forced to travel in an orbit at $r = \frac{3GM}{c^{2}}$. Is it possible to detect these spheres? What happens if I fall through ...
10
votes
0answers
56 views

What allows the modified Urca process to work at lower density than direct Urca in neutron star cooling? [duplicate]

Possible Duplicate: What allows the modified Urca process to work at lower density than direct Urca in neutron star cooling? This comes from an unanswered question over at physics.se: The ...
4
votes
3answers
3k views

Why do white dwarfs shine white?

The hotter something is glowing the more white/blue it appears. A dying medium sized star expands, cools and becomes a red giant for a while, but eventually it is going to gravitationally collapse ...
0
votes
2answers
46 views

What do moles and moles of various subatomic particles gathered together look like?

I wonder whether it is even possible to find the answer. If it is impossible to find out, why? Do moles of neutrons basically look like a neutron star? If so, what does one look like? How about ...