19
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Why do massive stars not undergo a helium flash
After H burning has finished, the he mass of the He core gradually increases, as does its density and temperature.
Low-mass stars have denser cores when they reach a temperature at which He is ignited....
- 118k
15
votes
Accepted
Does the average proton/electron density in a neutron star change with mass?
The ratio of neutrons to protons (and electrons, since the fluid is neutral) does depend on the overall density. In an ideal n,p,e fluid, the ratio is of order 100 to 1 at average neutron star ...
- 118k
14
votes
Accepted
How could a neutron star collapse into a black hole?
The scenario you describe may occur. On the other hand it may actually be that neutronisation in a white dwarf is the trigger for a thermonuclear type Ia supernova.
You may be misunderstanding the ...
- 118k
10
votes
White Dwarf and Degenerate Matter
The density of white dwarfs is not hypothetical, it can be measured. The short answer is that the density is so high that a stable star can only be supported by electron degeneracy.
Sirius B is an ...
- 118k
10
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Measures for the degeneracy from protons?
Stars are electrically neutral. In the optimal case for proton degeneracy, a star is made of hydrogen, maximising the proton number density. The number density of electrons is exactly the same.
Since ...
- 118k
10
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Accepted
Why can't neutron stars ignite and explode?
In a white dwarf, the dense matter is not in its lowest energy configuration. Energy can still be extracted from the white dwarf material by fusion, provided it can be ignited.
What exothermic ...
- 118k
10
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Accepted
Are white dwarf stars supported by proton degeneracy as well?
Straightforwardly no.
For a start there are almost no free protons inside a white dwarf. They are all safely locked away in the nuclei of carbon and oxygen nuclei (which are bosonic).
There are a few ...
- 118k
10
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Are white dwarfs made of carbon or electron degenerate matter?
Most white dwarfs consist of fully ionised carbon and oxygen atoms$^1$. Each carbon nucleus must be accompanied by 6 electrons and each oxygen nucleus by 8 electrons. The electrons are essentially a ...
- 118k
9
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Can the Sun contain degenerate matter?
The answer to whether a normal star can contain a core of degenerate neutrons is a yes. Thorne & Zytkow 1977 produced numerically models where a neutron star becomes embedded in the center of a ...
- 34.1k
7
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Accepted
Electron Degeneracy Pressure
Z is the atomic number, A is the atomic mass.
A white dwarf is typically made of carbon (A=12, Z=6) or Oxygen (A=16, Z=8). So Z/A = 0.5.
- 118k
7
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Why do massive stars not undergo a helium flash
More massive stars indeed have higher pressures, but what's key is that they also have higher temperatures. After leaving the main sequence, they reach core temperatures of a few times $\sim10^8$ ...
- 34.1k
7
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Are white dwarf stars supported by proton degeneracy as well?
Proton degeneracy is not important, because its effect is much smaller -- much like nuclear particles in theory also are dictated by gravity, but the electromagnetic and nuclear forces are dominating, ...
- 493
7
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Accepted
Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?
The test to see whether degeneracy pressure is going to be significant is to compare $kT$ with the Fermi energy $E_F$
The Fermi energy is the energy level up to which all energy states would be ...
- 118k
6
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Can the Dark Energy be Pauli pressure?
There are several reasons dark energy cannot be pressure due to the Pauli exclusion principle. First of all, pressure does not cause expansion of the universe, because pressure is not a force-- ...
- 5,170
6
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Are gas giants supported by thermal pressure?
I am not sure what you mean by "thermal" pressure. Jupiter is supported by pressure, just like all objects that are in (approximate) hydrostatic equilibrium.
That pressure is provided by your ...
- 118k
6
votes
How massive can a cold solid object be?
You cannot have a large mass of "normal" matter that is both cold and in equilibrium. Cold matter will collapse towards its minimum energy density configuration. For masses below the "...
- 118k
6
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What would happen to a gas planet if its core mass goes beyond the Chandrasekhar limit?
Gas giants like Jupiter consists mainly of Hydrogen and some Helium. If you gradually add mass to these planets then core temperatures will rise gradually and a stage will come where they will ignite ...
- 518
6
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Why do massive stars not undergo a helium flash
Massive stars do not undergo helium flash because they have core temperatures high enough to prevent the helium core from becoming electron-degenerate. Check here for some more information.
Therefore, ...
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5
votes
Accepted
If Jupiter were to absorb all other planets in the solar system, would it reach degeneracy pressure?
No, hydrogen burning doesn't start until 82 $m_{\rm Jup}$ and deuterium burning starts at 13 $m_{\rm Jup}$, so evidently 1.4 $m_{\rm Jup}$ is not enough for this experiment.
Your misconception is ...
- 9,088
4
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Accepted
What would happen to a gas planet if its core mass goes beyond the Chandrasekhar limit?
@Knu8 was right that adding mass to a gas giant will turn it into a star long before the gas giant could become a white dwarf or neutron star. But that works if you add fusionable material such as ...
- 752
4
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What escape velocity would quark stars have?
The escape velocity (in terms of Schwarzschild coordinates) from the surface of a quark star will be given by
$$ v = c\left(\frac{r_s}{r_q}\right)^{1/2}, $$
where $r_s$ is the Schwarzschild radius, $...
- 118k
3
votes
Can the Sun contain degenerate matter?
There are problems with the scenario outlined above.
Firstly, if the CNO cycle were to operate, it would have to operate for millions/billions of years to noticeably affect the relative abundances of ...
- 118k
3
votes
If Jupiter were to absorb all other planets in the solar system, would it reach degeneracy pressure?
The above answer handles the question as you posed it, but perhaps it should also be addressed the way you phrased the question in the title. Are you imagining that degeneracy pressure is associated ...
- 5,170
3
votes
Accepted
Electron Degeneracy Pressure and the Pauli Exclusion Principle
Basically, the Pauli exclusion principle says that two fermions (in this case, electrons) can't be in the same quantum state. To expand: No two electrons in an atom can share the same numbers for ...
- 34.1k
3
votes
Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?
So then why would gas giant cores be electron degenerate, but not become hot enough for nuclear fusion?
Degeneracy isn't an on/off switch. It's a quantum mechanical aspect of pressure that is always ...
- 28.3k
3
votes
Accepted
Why does the Chandrasekhar limit affect white dwarfs differently?
Whether a white dwarf responds to the accretion of material by exploding or collapsing depends on the competition between energy being released in fusion reactions and energy being locked away by ...
- 118k
3
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Why does the Chandrasekhar limit affect white dwarfs differently?
There are a variety of white dwarfs with various compositions, and analysing how they detonate in a supernova (or not) is an topic under investigation. A simple model, described in "How is the first ...
- 91.3k
3
votes
What escape velocity would quark stars have?
Adding to the other answers and in particular ProfRob's answer: Buchdahl's theorem states that the minimal radius of a static, spherically symmetric matter configuration that acts as a perfect fluid ...
- 10.5k
3
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Hypothetical upper and lower bounds for Chandrasekhar limit based on composition?
Yes, you are correct in so far as what the Chandrasekhar limit is for a white dwarf supported by ideal electron degeneracy pressure and using a Newtonian equation of hydrostatic equilibrium.
Neither ...
- 118k
2
votes
How could a neutron star collapse into a black hole?
In Layman's terms, the Pauli exclusion principal wouldn't need to be overcome to form the black hole. A Neutron star of a certain size will shrink below it's Schwarzschild radius naturally. That's ...
- 22.9k
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