Questions tagged [stars]

Stars are astronomical bodies that are (usually) mainly composed of Hydrogen, Helium, and Lithium. They are massive enough that their gravity compresses the matter to the point where nuclear fusion occurs, which creates a lot of heat and tends to make stars output radiation along a blackbody curve. Typically the radiative output is significant in the visible spectrum making stars very bright objects.

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How would a quark star maintain degeneracy near the surface?

I'm still not exactly understanding how a quark star could possibly exist for more than a fraction of a second. Neutron stars are already hypothesized to have degenerate quark matter at their cores, ...
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By how much does starlight heat the Earth?

According to this, the stars in the night sky have a cumulative magnitude of -6.5. This is very dim, so I expect the heat generated to be tiny, but I'm wondering how tiny. Moonlight does measurably ...
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Effect (if any) of strong(ish) gravity radiation on stars

Two black holes merge, and a good few percent of their total mass is converted into gravitational radiation. Years or decades later, the resulting gravity wave passes through nearby stars. Does it ...
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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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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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Surface UV exposure with cooler star

If the sun's surface was ~ 4000K (and earth closer to compensate), the UV component of the radiation would be less. However, UV makes ozone via photolysis of oxygen. Also, the stratosphere would ...
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How does Buchdahl's interior solution satisfy the Einstein field equations?

I was reading Schutz A First Course in General Relativity (2nd Edition) Section 10.6, where the Buchdahl exact solution was written down as follows: For $Ar'\le\pi$, $$ \exp(2\Phi) = (1-2\beta)(1-\...
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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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Celestial Body Approaching Speed of Light, “Observed” as a Black Ellipsoid?

I have an interesting question, one which I think may not work haha, but please bear with me. Let's work with our sun, with mass of about $2 \times10^{30}$ kg. According to the following formula, ...
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How can we evaluate the ratio of abundance of Carbon to Li, Be and B?

In stars' nuclear processes, if the triple $\alpha$ reaction explain why Carbon is much more abundant than Li, Be, B, how can we evaluate the ration of abundance to ~$10^5$ times ? Is it possible to ...
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Frequencies of stellar g-mode oscillations in astroseismology

It's a simple derivation that in a gravitating fluid, if the density decreases with height then a perturbed fluid element should oscillate at the Brunt-Vaisala Frequency, $$N^2 = - \frac{g}{\rho_0} \...
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351 views

Slope of main sequence in HR diagram

In the HR diagram, what causes the change of slope (more flattened) around the area marked with $X$? This corresponds to luminosity of $\sim 1 L_{\odot}$ and temperature $~6000-8000 K$
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Spin during gravitational collapse

During or upon the ending of the gravitational collapse of a rotating star, can it be reasonably hypothesized that a collision between particles of half-integral spin might result either in a change ...
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1answer
55 views

Equations of state for white dwarf stars

I am dealing with some model describing the given composition of a white dwarf made with photons, degenerate electrons, positrons and ions. From that, I can get tabulated values of densities ranging ...
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72 views

Why stars don't precess?

Assuming that rotation of stars, galaxies etc is determined basically randomly, the question is: why do all space objects rotate so 'neatly', with little or no precession? And what precession there is ...
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Do Efimov states contribute to fusion reactions other than the triple-alpha process?

An Efimov state is a three-body quantum state in which each two-body subsystem is unbound, but the system as a whole is bound because of the large s-wave scattering length. Intuitively, one can ...
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Minimum energy principle for stars

In Townsend's Black Hole lecture notes, he says that at equilibrium, $E = E_{grav} + E_{kin}$ is a minimum, where $E_{grav}$ is the gravitational potential energy $-\frac{GM^2}{R}$ and $$E_{kin} = nR^...
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Star formation rate in different galaxies

I was looking for some scale to compare my result of star formation rate and see if it is moderate or high or low. But I couldn't find any scale. Is there any paper related to such scale where Star ...
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How does metallicity affect stellar evolution?

The main sequence evolution of a solitary star depends most of all on its initial mass. Other factors influencing its evolution are the initial metallicity, rotation and magnetism. Question: how does ...
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Physical relation between adiabatic constant $\gamma$ and polytropic index $n$

I am study about stellar model of stars by using polytropic equation of state $$P=k\rho ^{\gamma}$$ or $$P=k\rho ^{1+1/n }.$$ I studied that different values of polytropic index $n$ describes ...
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Galactic bars and star formation

I have recently been reading on barred galaxies and am confused as to whether they aid or obstruct star formation as a general rule. Some papers state that they aid star formation, whilst others ...
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Im trying to prove that a star can be described by a polytrope by deriving the polytropic relation of $P\sim p^n$ from the stellar structure equations

Suppose that in a star, the only source of energy generation is radioactive decay, so the energy production per unit mass is constant and independent of density and temperature. Further suppose that ...
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Theoretically, Is it possible to create a nova by firing large masses into a sun?

In a science fiction story (Bobiverse) a nova is created by accelerating two small planets at relativistic speeds into a sun from opposite sides.The shockwave creates hydrogen fusion on opposite sides ...
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Shooting Star Anomaly

Tonight I was walking home from the supermarket and saw an unusual shooting star. It appeared at a point in the sky, bright red and accelerated to a visible extent far faster than any other shooting ...
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Can Thorne–Żytkow object (heavenly body) exist in universe?

Can Thorne–Żytkow object (heavenly body) exist in universe? It's a new concept I came across. Are there such heavenly bodies in universe? It's a heavenly body in which a neutron star is present inside ...
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Is the surface temperature of the sun constant?

I was just wondering that during the suns mains sequence would it maintain a constant temperature at the surface and only cool once the hydrogen in its core runs out, or is it always slowly decreasing?...
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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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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
102 views

star gazing from the bottom of a well

I have read that it is a myth that you can see stars in daylight if you stood at the bottom of a well, however, if you stood at the bottom of a well at night, or built a long non reflective tube and ...
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Gödel's Solution as background for a star patch

In Gödel's "Example of a New Type of Cosmological Solutions of Einstein's equation of Gravitation", all prior cosmological solutions with a non vanishing energy density have a property of all world ...
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83 views

Where can I find values for apparent brightness of stars?

I'm in high school and doing a project. I want to calculate the distance to stars using their luminosity and apparent brightness, from the equation $b=\frac{L}{4 \pi d^2}$. I have found values for ...
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what is the telescopic retinal illuminance of a star?

What is the retinal illuminance (in trolands) or luminance (in $cd/m^2$) of a star image viewed through a telescope? I'm looking for a formula that will calculate this value for input values of star ...
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Number of stars with apparent flux

The stars in our Galaxy have luminosities ranging from $L_{\text{min}}$ to $L_{\text{max}}$. Suppose that the number of stars per unit volume with luminosities in the range of $L$, $L+dL$ is $n(L)dL$. ...
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Influence of matter of a star on masses of neutrinos

It is well known that if neutrinos has masses then from Dirac equation it follows that they propagate (in vacuum) as a eigenstates of mass (not as eigenstates of interaction). It's wave function is of ...
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Locating a possible habitable zone in an ordered hierarchal septenary star system?

I'm writing a story about potential off-world colonization in the dawn of interstellar commerce, and despite such a plot necessitating some degree of FTL travel I'd like to keep the rest of my science ...
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how to calculate the amount of mass ejected from a stellar system?

I need to write a python program to find the amount of mass ejected from a stellar system and how much is retained. for this I need to calculate the quantity $$\int \rho (\vec {r}) f (\vec {v} (\vec ...
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Dust mass-loss rate from a massive star given a set of parameters?

I've been looking for examples at how mass-loss rates are determined. I'm studying a circumstellar dust shell ejected from a Wolf-Rayet star. I have some parameters like, expansion velocity of the ...
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If entropy is positive, then why do stars form from nebulae?

Sorry if I have so many misconceptions with this questions, but I guess that's the point of asking questions. If entropy, the measure of disorder, is always positive, then how come a star could form ...
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What is the definition of the “stellar angular diameter” in stellar astronomy?

(Following the definitions here: http://arxiv.org/pdf/astro-ph/0509535.pdf ) What is the "stellar angular diameter", as measured by astronomers specializing in stellar astrophysics? Using the ...
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Origin of Stellar Nurseries

What is the mechanism thought to cause huge stellar nurseries to form e.g. eagle nebula?
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Star collision observation

What would these scenarios look like in real world? I mean, what the result would be?: 2 stars (not necessarily same mass) will collide "side by side", like in, they originally were traveling ...
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The standard textbook on supernovae?

This is a straightforward question: What is considered to be the standard treatment of supernovae? Could be a textbook, lecture notes, review article, etc.
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Do the different observed Type Ia supernovae have similar explosion energy?

I have been trying to read about the energetics of observed supernovae for some time. And while the observed core-collapse supernovae have many scientific papers about them trying to estimate the ...
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Why does the sun and gas planets in our solar system weigh more than the earth?

I was reading a space.com article about What Is The Sun Made Of? The article says that the sun is made of plasma and gas. If this is the case, how is it that the earth which is solid weighs less than ...
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Cross section for photon-electron interaction in high temperature, high density plasma

I need a plot for the cross section of the photon-electron scattering at high density and high temperature. I am working on a project for which I have to calculate the opacity of a hot, dense plasma (...
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Can we go beyond Casimir Effect 2 plates Experiment?

Every one knows and talks about the 2 plates experiment but I woud like to go beyond that even if only in theory. Some say, the by pulling the plates apart, it would create a "distortion" ...