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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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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Calculating apparent density of stars in sky, given an area and distance away from my viewpoint

According to this source, there are $5077$ visible stars in the night sky, and a full sky area of $41253$ square degrees of sky. This makes for a density of $0.12$ stars per square degree of the sky. ...
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Death of Stars and Red Giants [duplicate]

As a matter of fact, I was learning stellar astrophysics where I couldn't understand the chain of events at the time of death of stars, Once the hydrogen fuel core is exhausted, the stars start ...
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Jupiter-sized planet orbiting a white dwarf?

I read this news about a Jupiter sized planet orbiting a white dwarf. It is still puzzling to the scientists that how it remained as a single piece. NOTE: I went through the Astro.SE link given in ...
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Does the Sun have enough gravitation to bind its hydrogen/helium plasma?

"Does the Sun have enough gravitation to bind its hydrogen/helium plasma?" So my question arises from the fact that high energy (or high temperature in other words) hydrogen or helium gas ...
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Why is Stephenson 2-18 so large?

How does a star as large as Stephenson 2-18 get this big? It is 2500 times larger than the sun. Did it start out as a large star with a lot of gas left over that gradually consumed the gas growing ...
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Equations for developing a hypothetical Solar System

I am currently going down the rabbit hole of writing a story but I would like it to be set in a universe which is believable. Therefore I am trying to create a hypothetical solar system in which the ...
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Matching Metrics of Gravitational Collapse in Weinberg's Gravitation and Cosmology

In chapter 11, section 9 of Weinberg's Gravitation and Cosmology, the metric of a collapsing pressureless star of uniform density $\rho(t)$ is derived. In comoving coordinates, it essentially looks ...
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Astronomical objects that should have magnetic bubbles similar to those found by the Voyager probe at the edge of our solar system

I've known about the existence of magnetic bubbles at Solar System's edge from a video edited by NASA from an official channel of YouTube, I refer [1] (as explicitly stated in the title, it was a ...
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Why are black holes so special? [closed]

When reading about black holes, I have also read about things relating to black holes like holographic principles, parallel universes, black hole connecting multiple universes, etc. But black holes ...
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Could you know in advance specifically when a star will go supernova?

I've been thinking about star trek 2009 and star trek Picard in which they happen to talk about a sun inside a fictional solar system which goes supernova destroying a particularly important planet to ...
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Why is there more lead and mercury in the universe than gold?

I am watching a Science Channel program on the collapse of massive stars and it got me wondering... What is the distribution of heavier than iron elements in the universe. (It is my understanding ...
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Why don't main sequence stars continuously expand?

I understand main sequence stars become subgiant when hydrogen is depleted in their cores and they start hydrogen shell burning. But I don't understand why this process is divided into two distinct ...
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How do we experimentally estimate the luminosity of a distant star?

While calculating the matter density of the universe, we need to find luminosity. How do we experimentally estimate the luminosity of a star?
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Definition of eclipsing binaries?

In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
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Does light return to its starting point in a closed universe?

I was reading about the possibility that our universe could be a closed sphere. from Sean Carroll “in a closed universe, one that wraps around on itself to form a compact geometry, like a three ...
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How come gravity generates enough pressure to start a fusion reaction in stars even though it is the weakest force?

Given the fact that gravity is the weakest of all forces, how does a gas cloud manage to collapse on itself under gravity and start a fusion reaction, outweighing the electromagnetic and nuclear ...
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Books for Solar physics

I am thinking about applying for an internship at a university under a professor who does Helioseismology. What resources would you recommend me for being ready for such an internship? Can you suggest ...
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What would happen to the Sun if you reflect all its emitted e.m. radiation back? [duplicate]

What would happen to the Sun if you would reflect, in whatever way, all the outgoing electromagnetic radiation (Solar winds can be neglected)?
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Number of seemingly brightest stars: minimum around G-stars

This plot gives the amount of the seemingly 10000 brightest stars. Can someone help me to explain why there's a minimum at number 3, I know how to explain 1 (there are less big stars) and 2 (small ...
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Stellar nucleosynthesis

I would like to learn more about fusion in stars. The question I have is whether there exists a graph showing exactly which elements take part in the reactions. Here, I managed to find some data ...
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Investigating colour of a star when in motion [closed]

The star Alpha Centauri is 4 light years from Earth. For an astronaut travelling at $c/2$ from Earth to Alpha Centauri. So, this apparently means The colour of a distant star perpendicular to the ...
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Trouble understanding exactly why core of sun does not mix with outer layers

I’ve had trouble understanding exactly why there is not more mixing of plasma at the core of the sun with the outer layers. I understand the difference between the radiative zone and the convective ...
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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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Comparing Luminosity of a star calculated from absolute magnitude to its actual luminosity

If the luminosity of a star is calculated in terms of the solar constant (the suns luminosity) by comparing the absolute magnitude (apparent magnitude at a distance of 10 parsecs) of the star in ...
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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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Relation between central density and stellar mass (2)

Comparing stars with different masses, the central density is lower in a heavy star than in a low mass star (assuming that each star has the same composition and has just reached the stage in which it ...
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What will be the mass of the sun when the core is depleted of hydrogen about 5 billion years from now?

Our sun converts 600 million tons of H to He every second, that is 5 million tons of matter into energy through nuclear fission. However, as the core of the sun continues to shrink the outer layers of ...
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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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Understanding the Chandrasekhar limit for white dwarfs and its relation with supernovas

So if I understand correctly, the Chandrasekhar limit ($\sim 1.4 \ M_{\odot}$) is the maximum mass that a white dwarf can have. Beyond this mass, the degeneracy pressure of the electrons can no longer ...
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Stellar structure integration

I have some issue regarding the stellar structure. I know analytically the equation of state, and I have been asked to build the structure of the star from these two equations $\frac{dP}{dr}=-\frac{G ...
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Why doesn't the nuclear fusion in a star make it explode?

I have a rather naive question. In stars such as the Sun, what prevents the whole thing exploding at once? Why is the nuclear fusion happening slowly? I can only assume that something about the fusion ...
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In fusion inside stars (sun) or very hot gasses, how do the electrons get bound and what about tritons and D-T vs D-D fusion?

Most texts I've read focus on just the nuclei to begin with, but eventually start talking about Helium (or other) atoms and isotopes. A few aspects aren't clear to me and I'd be grateful for some ...
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Solving coupled integral + differential equations for ionoization and combination of gases near a star

The following set of coupled differential + integral equations appear regularly in the literature (e.g Osterbrock, "Astrophysics of Gaseous Nebulae and Active Galactic Nebulae"): $ n_H(r) \int_{\...
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Electron degeneracy in white dwarfs

Consider a plasma in a star. Now in a plasma electrons are so excited that they can no longer be held by the electromagnetic field of the nucleus. But then when we are talking about cores or red ...
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How are the relative distances of celestial objects from the Earth calculated using observations at a single time instant?

How does one find the distances of celestial objects in the night sky, such as the Moon and the stars, from the Earth using a snapshot of information (including, say, the intensity and wavelength of ...
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What is a simple argument to prove that the stars in the sky are further away from the Earth than the Moon?

How do we know, without using modern equipment, that the stars are further away than the moon in the night sky? Further, is there a simple and actionable argument to prove that this is indeed the case?...
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When the star formation begins?

We can separate the history of the universe in different epochs. Radiation dominated epoch, matter dominated epoch, and dark energy dominated epoch, and we can divide the epochs in different ways. ...
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Why is the $\rm CNO$ cycle is much more efficient than the $p$-$p$ cycle?

Why is the $\rm CNO$ cycle is much more efficient than the $p$-$p$ cycle?
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A question on Przybylski's Star

Przybylski's Star is a rapidly oscillating AP star of 4 solar masses, 355 light years from earth. It contains high levels of unusual elements like strontium, holmium, niobium, scandium, yttrium, ...
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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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Measuring the interior temperature of the Sun

We frequently measure the "temperature of the Sun" using Wien law: $\lambda_m T = b$ where $b$ is the displacement constant, $\lambda_m$ is the peak wavelength obtained from the spectrum, and $T$ is ...
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Is it possible to know in advance that Alpha Centauri has exploded?

Alpha Centauri is 4.3 light years away. If it exploded suddenly, would we be able to know this in advance? As the light from the supernova will not reach us before 4.3 years.
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distinguishing redshift from star's color

How do scientists find out the true color of the star's light as well as the true doppler shift (relative speed)? Seems to me you wouldn't know how to separate out those 2 values.
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How to tell a population 3 star in red shifted galaxy?

I read that population 3 are metal poor stars especially those very very massive ones will quickly exhaust their fuel and goes into supernovae when their internal pressure drops due to pair ...
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How does a spectral line tell us about the magnetic field of a star?

An absorption line in the spectrum can indicate the abundance of a chemical element in a star; but according to NASA, it can also tell us about the magnetic field of the star. Can a spectral line ...
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Why is the second stellar structure equation first-order ODE?

the 2nd structure equation is first order, but we seem to have two boundary conditions (e.g., $dP/dr = 0$ in a star’s center and $P=0$ at the surface) – but first-order ordinary differential equations ...
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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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Are the muon/tau neutrinos produced in the Sun? If not, then where?

I was reading about Solar Neutrinos, and apparently they are all Electron Neutrinos. However, there are two other types of neutrinos, the Muon and Tau Neutrinos. Does the Sun produce them? If not, ...

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