Questions tagged [white-dwarfs]

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1answer
206 views

What fuel is J005311 burning?

J005311 is two white dwarf stars that have merged in such a way, that, well they merged instead of exploding. (Only 7 or so such mergers have been found.) Its stellar wind is blowing at 16,000 km ...
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1answer
46 views

Does electron degeneracy pressure decrease over time in a star?

As far as i understand, electron degeneracy pressure relies upon the confined electrons having a lot of kinetic energy, which causes them to push 'outwards', counteracting gravitational pressure in a ...
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1answer
71 views

Pauli Exclusion and Black Holes [duplicate]

Pauli exclusion principle states that 2 identical electrons cannot be in the same state, where state includes a spacial component. I have heard that, in order to avoid being in the same state, in a ...
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1answer
59 views

Why are more massive white dwarfs smaller?

I understand that a white dwarf is supported by the Pauli Exclusion Principle and that the larger the gravitational force against them, the closer the electrons must pack. But I have two queries: ...
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1answer
35 views

Wind-fed Accretion and White Dwarf stars

Can a White Dwarf star in a binary system accrete matter via the Wind-fed accretion process?
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1answer
47 views

Behaviour of a star as it approaches Ultrarelativistc limit

By considering the potential energy of a degenerate star of mass $M$ and radius $R$, I can use dimensional arguments to show that the radius of the star depends on its mass as: $$ R ∝ M^\frac{2-n}{...
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1answer
103 views

Luminosity of a white dwarf

Why in an H-R diagram the white dwarfs are at the bottom left? I understand that they would have a high temperature when they are formed, and so at that instant shouldn't they have a high luminosity ...
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0answers
19 views

Where are the high mass White Dwarfs that are going to create type 1a SN

The mass distribution of WD stars is explained at Why is the white-dwarf mass distribution highly peaked?. However this mass distribution shows very few stars that are about to exceed the WD limit of ...
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0answers
40 views

What fundamental force is at play in electron degeneracy pressure? [duplicate]

For example 2 electrons repel each other because they experience electromagnetic force, matter particles attract each other because they exert gravitational force on each other, fusion is possible ...
0
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1answer
69 views

Could a sufficiently massive Dyson Sphere under very specific conditions depend solely on electron degeneracy pressure for structural integrity?

Stuck in an argument. I claim this is theoretically possible: Provided you could build a type 1 Dyson Sphere, made from a supposed material that rivals the structural integrity of a white dwarf, i.e. ...
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0answers
28 views

Would a Dyson sphere face physical limits faced by white dwarves?

During a recent online discussion, one of the participants made the claim that a Dyson sphere would be limited in mass by the Chandrasekhar limit. Attempts to solicit evidence for this claim were ...
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1answer
154 views

How to get the Chandrasekhar Limit from a plot?

at the moment I am trying to understand, how to obtain the Chandrasekhar mass limit from a plot like shown above. Because for $n$ = 3, the mass is independent of the radius of the white dwarf. But in ...
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1answer
199 views

What is the theoretical lower mass limit for a white dwarf?

This question in inspired by this other one, which asks what is the theoretical lower mass limit for a gravitationally stable neutron star (not the Chandrasekhar limit which is the upper mass limit ...
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207 views

What is the Chandrasekhar-Friedman-Schutz (CFS) instability, exactly?

I am confused as to what the Chandrasekhar-Friedman-Schutz (CFS) instability is, exactly. It seems to partially refer to this paper (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.24.611) ...
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5answers
106 views

How does gravity acts on the electrons to collapse a neutrons star or white dwarfs against the degeneracy pressure?

if electrons is considered as quantum particle in case neutron star (alluding to quantum statistics) how does gravity makes the star collapse? considering the fact that electrons are quantum particles ...
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0answers
204 views

What's the transition from “metal” to “electron-degenerate matter” look like?

Question: Say that we had metallic water and compressed it until it qualitatively resembled the state of matter in a white dwarf: what would that transition look like? Background (revised to be ...
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1answer
76 views

What does a redder galaxy mean?

I've been reading on the subject and I've repeatedly read that red galaxies are those with redder stellar populations which means (according to my readings) older star populations, with low star ...
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2answers
258 views

Where does the energy for electron degeneracy pressure come from?

I just watched a web video about white dwarf stars. It mentions that the star’s electrons flow among the degenerate matter. Since most of the electrons can’t be in the lowest state, due to Pauli’s ...
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1answer
2k views

Can nuclear fusion alone account for the energy output from type 1a supernova?

Unlike other supernova, which can vary in their size, Type Ia supernova are all about the same size. This is due to the fact that they are caused when a white dwarf star gains enough mass from its ...
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1answer
409 views

Why don't electrons and protons in a white dwarf combine before the electrons become ultrarelativistic?

I wanted to get a rough picture of how white dwarfs and the Chandrasekhar limit work. I wound up with an argument nearly identical to this one on Wikipedia up through the non-relativistic white dwarf. ...
4
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1answer
68 views

How to justify the maximal value of a star's magnetic field at surface?

In many lectures, it is stated that the maximal value $B_{\text{max}}$ of the magnetic field at the surface of a star can be found in Newton's gravitation theory by equating the gravitational ...
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1answer
231 views

White Dwarfs Mass-radius relation for different chemical compositions

The standard non-relativistic mass-radius relation of low mass white dwarfs is this : \begin{equation}\tag{1} R(M) = \frac{\mathcal{C}}{M^{\frac{1}{3}}}, \end{equation} where $\mathcal{C}$ is a ...
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1answer
56 views

Novae versus supernovae type Ia

Why are there any novae at all? My understanding is that once accretion on a white dwarf exceeds the Chandrasekhar limit, the white dwarf undergoes a supernova. Why then do some just simply go nova?
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1answer
162 views

White dwarf without Pauli

In a national pre-university physics exam pupils are asked to explain that the white dwarf Sirius B exhibits (unspecified) quantum properties by comparing the debroglie wavelength of the electrons to ...
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1answer
123 views

How does fermion degeneracy affect elastic scattering in astrophysical compact objects?

As I currently understand it, absorption processes or inelastic scattering involving fermions in a degenerate gas are strongly inhibited, because to change the fermion energy (or create a new fermion) ...
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4answers
217 views

Can stars contain neutron-star dense cores?

purely for curiosity: are there any conditions under which a small amount of neutron star matter (400 trillion grams per cubic centimeter) could be at the core of a star or planet? neutron star ...
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1answer
137 views

What are black dwarfs?

What are black dwarfs what does they do? Please don't put a comment that I mistook for a black hole I know what a black hole is and also know that there is no relation between them because black hole ...
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1answer
791 views

Why don't degenerate gases expand from heat?

Degenerate gases are excellent conductors of heat. However, the fermions that compose the gas will not expand outwards due to heat, except in incredibly high temperatures. Why is this? Does it have ...
6
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1answer
495 views

Why is the white-dwarf mass distribution highly peaked?

I am doing an undergraduate course in astrophysics. The lecturer mentions that observed white dwarfs have a mass distribution that peaks at around 0.6 solar masses. Consider the plot from https://www....
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2answers
670 views

How can a low-mass star increase its mass to 1.4 Msun?

In my astronomy class I learned that a only low-mass stars (< 0.5 Msun) will contract, and then become degenerate, until it is a white dwarf. However, we also learned about the Chandrasekhar limit, ...
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1answer
64 views

Pulsar-white dwarf binary

In the paper from Hulse & Taylor 1975 on the first discovery of a pulsar in a binary system, they conclude that the companion to the pulsar must be a compact object, probably a neutron star or ...
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2answers
100 views

What would happen if I gathered stellar sized masses of iron?

Lets say I had a bag that when turned upside would start pouring out iron shavings and never ever stop. Viola, there's my infinite source of iron. Now, lets say I just continued to dump this iron ...
2
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2answers
710 views

Why does the core of a low mass star contract after reaching electron degeneracy?

I am learning about the lives and deaths of stars with a solar mass of 0.4-2. What I understand is that once the star stops hydrogen fusion after using up all its hydrogen, the star leaves the main ...
10
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1answer
573 views

Does matter found at densities of white dwarfs “feel” more like a solid, liquid or gas?

I'm wondering what it would be like to touch or interact with very dense degenerate matter like this found at white dwarfs. I understand that white dwarfs are initially very hot, but for the sake of ...
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1answer
1k views

Gravitational binding energy of a white dwarf at Chandrasekhar limit?

I was trying to calculate the gravitational binding energy of a white dwarf just before it went on a type Ia supernova in order to calculate the kinetic energy of the ejecta, but I wasn't able to get ...
10
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3answers
627 views

How to cut a stone on a White Dwarf?

I've heard that white dwarf stars are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
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1answer
171 views

White Dwarf radius

So I've been reading this about white dwarfs, and various other sites about white dwarf stars. In all of them, they say that we can find the radius of a white dwarf by minimizing its total energy. I ...
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4answers
7k 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 (...