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Questions tagged [stellar-physics]

The science regarding the structure, formation and evolution of stars.

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35 views

Is there a relatively painless way to calculate the radius of a neutron star, given its mass?

I know there are different models based on, as I understand it, different equations of state describing the neutron star mass-raduis relation. I'm not sure what to do with that, though. My math isn't ...
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1answer
113 views

Where is nuclear fusion occuring in the Sun?

My understanding is that the sun is basically a sphere of hydrogen with a helium core, and that the hydrogen is undergoing nuclear fusion to produce helium. There are many images and cross-sectional ...
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0answers
30 views

Derive the virial theorem from hydrostatic equikibrium

Consider the equation of hydrostatic equilibirium as follows as applied to a stellar object: $$ \frac{dP}{dr } = \frac{-GM\rho}{r^2} $$ I know it is intimately related to the virial theorem but I ...
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2answers
73 views

Is there an equation for the amount of energy from a collapsing star BEFORE it creates a black hole?

(I could be phrasing my question incorrectly, so bear with me as I try to explain it.) Recently I've been very interested in the geometry and physics of black holes, so I started messing around with ...
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1answer
154 views

Could the singularity of a black hole just be an iron / dark matter sphere? [duplicate]

A singularity would break physics wouldn't it? How does a massive star collapse and suddenly fall into a point in space with no dimensions what so ever when it had a core and perfect balance between ...
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2answers
57 views

Do only 'giant stars' fuse large amounts of elements other than hydrogen and helium?

Do only giant stars initiate 'full-on' carbon (and higher element) fusion, even though red giants on the larger end of the spectrum create carbon and oxygen via producing helium per the CNO cycle?
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2answers
208 views

Why does a star die once it has iron?

I found out that iron is the death element for stars, but I couldn't find why can anyone knowledgeable on stars explain why iron causes the star to die?
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0answers
32 views

Strength of core-envelope coupling in stars

For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope? I understand that the core-envelope boundary is only (...
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1answer
49 views

Steady solution for flow in Boussineq approximation in star [closed]

I am trying desperately to find the solution indicated in this question : If I compute the equations on the 3 axis, I can't get the flow to be directed along $\vec{e_y}$ I have only : $$\dfrac{\...
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0answers
24 views

What is the rotation profile for radiative zone of Sun - Instability and convection?

I am exercising on Stellar Physics topics and in particular the questions below: 1) First of all on the rotation profile for the radiative zone: I know that unlike the convective zone, where the ...
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1answer
43 views

When a star undergo collapse in a binary system what effect it has on its companion star? [closed]

when a star in its lifetime fuses up all its hydrogen and then collapse under gravitational force, till the temperature inside become high enough to restart the fusion of helium and radiation pressure ...
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1answer
85 views

Does the sun have nonzero electric charge? [duplicate]

The sun is a star, meaning it's a ball of gas undergoing nuclear fusion in its core. The sun, like any other star, experiences line-driven stellar winds due to the transport of ions from its interior ...
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1answer
43 views

What particle interaction is most important for maintaining the equilibrium of a main sequence star?

For main sequence stars like the sun, balance against gravitational collapse is achieved with the pressure of the underlying plasma. My question is how much of this pressure is accounted for by ...
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1answer
27 views

Does an external perturbing potential appear in the gravitational Poisson equation

We could use any self-gravitating fluid for this question, but let's take a star as an example. Left alone, it's density is the source of it's potential and thus we have the simplest form of Poisson's ...
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2answers
918 views

Can we see emission lines in stars?

I read that stars show both absorption and emission lines. While how we see absorption lines is clear to me, I don't understand how (and when) we see the emission lines. Based on what I read in ...
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2answers
36 views

Derivation of pressure gradient stellar equation [duplicate]

I am trying to understand how to derive the following formula: $\frac{dP(r)}{dr}=-\frac{GM(r_<)\rho(r)}{r^2}$ The notes are as follow: Consider a star with COM and a shell: $P_1 - P_2 = -{\...
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2answers
156 views

Binary Stars In the Universe

Almost 80% of stars seen in the universe are Binary stars.What makes them so abundant in the universe? Why isn't there other numbers but exactly two that is abundant?
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1answer
77 views

What is meant by “stable/unstable to convection” in the context of the solar atmosphere?

In studying the Schwarzschild stability criterion (for the solar atmosphere); $$\left\lvert\frac{dP}{dr} \right\rvert\lt\frac{\gamma P}{\rho}\left\lvert\frac{d\rho}{dr}\right\rvert$$ From my notes are ...
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1answer
90 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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0answers
76 views

How does a neutron star collapse into a black hole?

Neither this answer nor this answer answers my question. I want to know more details of how a neutron star collapses into a black hole. One possible way it does so is once a neutron start is massive ...
7
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1answer
187 views

Triple-alpha reaction rate

I'm trying to find a general equation for the fusion rate of the triple alpha process. I found this equation: The rate of energy generated by this process as a power law in $T$, centered around $10^...
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3answers
119 views

Star formation from gas? [closed]

Considering the ideal gas law , where pressure is always positive, i wonder : How can gravity turn a gas into a star? Yes gas has mass too. But a light gas obeing the ideal gas law seems ...
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1answer
440 views

Stellar Isochrones, what are they?

So I have been reading and I am trying to understand what stellar isochrones are and what relationship they have to the Hertzsprung-Russell diagram. My understanding at the moment is that, the ...
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0answers
61 views

What portion of the total power emitted by the Sun comes from photons?

We usually talk about luminosity, which is the total power from emitted photons. The other sources are neutrinos and the solar wind (which includes protons and other particles). I assume that most ...
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0answers
127 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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1answer
112 views

Minimum size of a “water star”

So I had this weird idea the other day. We know that stars form from simple matter (dust, gasses, etc) forming a gravity well, attracting to each other, until the amount of mass and density in the ...
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1answer
89 views

Could we create an artificial sun? [closed]

based on dyson spheres.. imagine we construct an sphere of high radius R , then we fill the sphere with hydrogen, if the sphere is huge and the hydrogen is too then the gravity will make the ...
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2answers
45 views

Force Opposing Gravity in Stars

This seems like a fairly basic thing, but I've google around and I'm just not sure what to ask. I assume that, for example, in a star, there is a force of gravity compressing the stellar matter, and ...
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0answers
55 views

Why does hydrogen fuse in a star? [duplicate]

I have only had basic classroom experience with physics but I have done a lot of research on my own and I am wondering why a newly formed star or any planetary body composed purely of hydrogen will ...
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4answers
136 views

Energy Transport in stars

I'm trying to understand why convection is an efficient mode of energy transport in the outer layers of the solar interior. Could anyone give me a little bit of knowledge?
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1answer
63 views

Describing the Sun's interior

Can the interior of the Sun be described as an ideal gas? From my knowledge, to describe a body of gas as an ideal gas, the separation between the particles must be much greater than the size of the ...
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1answer
163 views

What causes a supernova explosion?

I know similar questions have been asked and answered. However, it is still not clear to me, so please bear with me if this is duplicate to some extent. The explanation goes like this - the core ...
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0answers
39 views

Do stellar model luminosities include neutrino losses?

I have had a sudden crisis in my understanding of the published outputs from stellar evolutionary model calculations. Usually these models output a "luminosity" that one can then use, along with the ...
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1answer
47 views

Radiation levels on inside surface of Dyson sphere

A couple of things occur to me: The Earth has a magnetosphere, which deflects the worst of the cosmic rays and radiation produced by Sol. We have an atmosphere which scatters and further attenuates ...
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1answer
168 views

Mass Luminosity Relation Review

I have read that exists a relation between the luminosity and the mass of a star $$\frac{L}{L_\odot}=\left(\frac{M}{M_\odot}\right)^a$$ with $a$ depending on the mass $M$. I have looked for a ...
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1answer
128 views

Is it possible for liquid metallic hydrogen to be present in a star

Liquid metallic hydrogen can form at extreme temperatures and pressures like that in the center of Jupiter and Saturn. I was just curious since some of the conditions can occur on stars is it ...
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1answer
50 views

Does the associated colour of a spectral class (red and class M, for example) come from the peak black body radiation of stars in that class?

Each spectral class O through to M has an associated colour. Class O stars are described as blue stars, for example. Is this colour determined by the peak wavelength of their black body radiation? Do ...
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0answers
71 views

Which theory do we use when dealing with the center of a star?

The center of a black hole is known as being one of the locations in spacetime that needs an unification theory between quantum physics and general relativity, because of having a large mass in a ...
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0answers
53 views

What happens when stars in an elliptical galaxy collide?

I don't mean when stars in a binary system spiral in and fuse together. I mean when they undergo a fast head on collision in an elliptical galaxy. I assume it's much rarer for stars to undergo that ...
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2answers
102 views

If we could withstand the temperature of Sun then could we actually stand on it? Does it have a solid surface or not?

If the sun's temperature were lower or we could withstand it, could we actually stand still on a solid surface or would we fall through into the depth of the sun? Is the sun's surface gaseous with ...
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1answer
105 views

Why does the H-burning Shell do the CNO cycle instead of the PP Chain?

A star that initially produces energy through the PP Chain will eventually exhaust its Hydrogen leading to a core contraction in order to increase the temperature to generate again nuclear reactions. ...
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3answers
1k views

What will happen if the nuclear reactions in the Sun stop suddenly? [closed]

If all nuclear reactions inside the Sun would have stopped somehow for ever then what all will be the consequences? My Attempt at the Question: Since the reactions were a source of Sun's ...
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2answers
199 views

About Planck stars

What is the main reason to argue that, with Planck stars, we would reach the Planck density much before (if I understood the idea of Planck star properly, correct me if I don't), we reach the Planck ...
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4answers
4k views

Where will the Goldilocks zone be when the Sun becomes a red giant?

In about 5 billion years, when our Sun expands into a red giant making our planet uninhabitable, where will the new Goldilocks zone be? Could life form on a new planet in the Goldilocks zone? ...
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2answers
208 views

How can a red dwarf have such an immense lifetime?

I understand what a red dwarf is, and that it is dominated by convection. But I still don't understand how the fusion processes in such a tiny star can keep going for the immense time predicted. ...
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2answers
153 views

How does the temperature evolve in a star collapsing into a black hole?

The temperature of a massive star is very high, and for neutron stars it is typically above $10^5\ \mathrm{K}$. (https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature) However, the model ...
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1answer
54 views

Stellar Ignition and Neutrino Energy

My question has to do with the following two pieces of information: When Fusion Ignites and a star is born, according to the Proton-Proton Chain, a positron and a neutrino are released when one ...
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2answers
126 views

Why the He core gets hotter and hotter? Is it because it shrinks?

I know that after a star in the main sequence runs out of H in the core, it will start burning H in the shells surrounding the (now) He core. (1) Why now the Hydrogen shells are hot enough for ...
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2answers
599 views

Can a hydrogen cloud directly collapse to form a black hole?

Does a cloud (essentially a nebula) have to turn into a star or can it directly become a neutron star/black hole? I might've read somewhere that some primordial black holes might have formed this way, ...
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1answer
37 views

Book about the sun or stars in general

I would be interested to know if there are any popular science books on what we know about the physics and processes in our sun. It may possibly be a book about stars in general, but since in recent ...