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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Density of iron and hydrogen in plasma [closed]

Solar models model the Sun's core as a dense plasma. I have not seen discussion about relative mobility of various elements in such an environment. What is the effective density of iron in plasma vs ...
Craig P's user avatar
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Obtaining TOV equations

I am trying to obtain the first TOV equation $$ (\rho+p) \frac{\mathrm{d} \Phi}{\mathrm{d} r}=-\frac{d p}{\mathrm{~d} r} $$ using the metric $$ \mathrm{d} s^2=-\mathrm{e}^{2 \Phi} \mathrm{d} t^2+\...
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If a star's luminosity doubles, does its received flux double?

If the luminosity of a star increases or decreases in some way, would the received flux increase or decrease by the same amount (linearly) or would it change by the square of the luminosity (inverse ...
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Is there a way to calculate the habitable zone distances of a star?

What would you need to calculate the habitable zone distances of a star? I am aware of the Stefan-Boltzmann Law and Wein's Law to calculate the Luminosity of the star, and that the flux decreases with ...
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Is the sun multinucleated or is there just one point at or near the center of the sun where fusion is occurring?

I was just reflecting upon my thinking and probably any illustration in books or movies: I assumed a single general area near the "geographical" center where the actual fusion occurs. But ...
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A general theory of convection currents using continuity equations

In an Astrophysics & Cosmology summer programme I attended last summer at UCL we were taught that stars seem to transport matter from the regions near the core to the surface through convective ...
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Luminosity and absolute magnitude relationship

Context : an exercise gives the temperature, mass, distance and apparent magnitude of Sirius B and asks to calculate its density. One key step of the calculation is to get the luminosity from the ...
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What if Phoenix A collided with UY Scuti

What if Phoenix A collided with UY Scuti? Phoenix A is estimated to be 100 billion times bigger than the suns radius, while UY Scuti is estimated to be 1700 billion times bigger than the sun. What I ...
Kellan Heerdegen's user avatar
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Can stars bend light?

Is it possible for a star to be so big that its gravity can bend light like a black hole? If so, would the star appear dark or bright, or would it collapse on itself?
Kellan Heerdegen's user avatar
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Determining star position and velocity to deduce closest approach?

I am trying to replicate the results found for Gliese 710's closest approach of ~0.05 parsecs in 1.3 million years approximately. I thought that by plotting the sun at (0,0) and using the stars ra,dec,...
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Are black holes XXXL stars?

Am I right to think that black holes are stars that are so dense and heavy that radiation and matter cannot leave from it's surface?
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How do neutron stars overcome neutron degeneracy?

In a white dwarf, the star is prevented from collapsing due to the Pauli exclusion principle. If the star is heavy enough, the protons in the star will capture electrons, forming neutrons and ...
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Luminosity of stars

Good afternoon, I am attempting to calculate the ratio of temperature and luminosity between two stars, one entirely made of iron and the other of hydrogen, with the same volume. To do so, I have ...
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How is the trajectory of a star found relative to the Sun?

So i know we can get radial velocity by measuring blue shift and then we can use the distance to the star and its proper motion to get its tangential velocity. In the case of Bernards star, its ...
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What mass fraction of a main sequence star produces energy?

Only some fraction of the total mass of a main sequence star produces energy in the star's centre through the pp-chains, or in heavy stars, the CNO-cycle. My question is about the mass fraction where ...
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Massive star evolution leading to white dwarf?

Is it possible that a star with an initial mass greater than 12$M_\odot$ loses so much mass in the giant phase that it eventually becomes a white dwarf? If it is possible, what constellation or ...
gamma1954's user avatar
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Why are the hottest stars appear mostly in blue or blue-white? [duplicate]

Does it have to do with anything regarding wavelengths and frequencies..
John Titor's user avatar
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How to measure the ratio of a planet's radius to a star?

I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information. One of ...
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Number of red giant phases for stars between 2.2 - 8 solar masses

It is my understanding that stars the size of our sun will go through two red giant phases. The first one will occur when fusion of hydrogen to helium begins to happen in a shell surrounding the ...
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Hills Mechanism

The Hills mechanism postulates that when a stellar binary system is perturbed by a supermassive black hole (SMBH), the tidal forces at play result in the capture of one star while simultaneously ...
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What is the most highly charged celestial body in the universe?

Generally speaking, the universe is electrically neutral and the universe abhors an unbalanced charge. Wherever there is a positively charged object, you can bet there is a negatively charged object ...
enigmaticPhysicist's user avatar
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Color temperature and space

I often think about the universe and lately about the color spectrum. so I wanted to ask how much the temperature of the body depends on the color. the hottest star I've found is 200,000 k and its ...
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How fast is the naked-eye visible transition of a main sequence star to a giant? [duplicate]

I know the evolution of a main sequence star to a giant is a process that takes millions and millions of years, but how fast is the VISIBLE change? Basically, will our sun, for example, slowly grow to ...
blacktopshaman's user avatar
14 votes
2 answers
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Is gravitational binding energy or gravitational self-energy a source of gravity?

The gravitational binding energy or self-energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. Equivalently, the ...
Manuel's user avatar
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How can there be supermassive stars of 10000+ solar masses?

Wouldn't such supermassive stars blow themselves apart first via radiation pressure (per the Eddington limit)? But they apparently exist, or at least are plausible: Assistant Research Fellow, Ke-Jung ...
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Luminosity effect in stellar spectral classification

“Atoms with small ionization energy,Ir,will have a higher ionization in the atmospheres of giants than in those of dwarfs, and the atoms with large Ir will behave in the opposite way. This ...
teacher's user avatar
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Salpeter mass function - past paper question [duplicate]

I'm doing a past paper and this is the question I'm struggling with (it's a standalone question with no other information given outside of this screenshot): To answer it, I used the Salpeter mass ...
user374355's user avatar
1 vote
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What is the total energy of newtonian polytrope stars of index $n > 5$?

In classical newtonian theory, we could find a general expression for the gravitational potential energy of a polytrope sphere (of pressure $p(\rho) = \kappa \rho^{\gamma}$, where $\gamma = 1 + \frac{...
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What is the equation of state (EoS) of a polytrope in general relativity?

I'm trying to numerically integrate the TOV (Tolman-Openheimer-Volkof) equations, using Mathematica. The code works, but I'm having issues with the polytropic equation of state (EoS). The equations ...
Cham's user avatar
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What are the hex color code equivalents for the different classifications of stars?

Stars appear to be of various colors based on the visible light they emit. I am wondering if there is a hex color code that can be considered to be typified or average for the various classifications ...
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Olbers' paradox and thermodynamics? [closed]

So consider our universe as an isolated system which has reached thermal equilibrium. Now using the first law of thermodynamics: $$ \underbrace{T dS}_{\text{Total energy}} = \underbrace{P dV}_{\text{...
More Anonymous's user avatar
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Could electron "Stars" exist? [duplicate]

Is there a point of balance where the gravitational pull of a sphere of electrons is equal to their electromagnetic repulsion? That is to say, could it be possible to create stars that are made purely ...
Nick Revenco's user avatar
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1 answer
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Will Hawking radiation violate baryon number conservation around gravitating bodies other than black holes?

Numberous articles discussing a recent research paper suggest that even stars and planets will eventually radiate away their mass like hawking radiation. My question is will this violate baryon ...
Keith Reynolds's user avatar
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Effect of Sun temperature on the thermosphere

Correct me if I’m wrong here. The thermosphere is hot due to its absorption of moderately high energy UV radiation. (<200nm) Cooler stars emit fewer high energy photons. So if the Earth orbited an ...
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What’s the lightest you could make a "star" if you made it out of different materials?

What’s the lightest you could make a "star" if you made it out of different materials? How large would the "star" be? For example according to here https://astronomy.stackexchange....
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What's the nearest star that could go Supernova in the near future?

https://en.wikipedia.org/wiki/IK_Pegasi B is the nearest supernova candidate, but that white dwarf that's part of the system won't go supernova for around 2 billion years. What's the nearest star that ...
blademan9999's user avatar
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7 votes
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Why are black holes sometimes formed without supernovae?

I've heard that very massive stars can sometimes collapse into black holes without creating supernovae. How does this happen? (I suspect it's something to do with the relative lack of Urca process ...
blademan9999's user avatar
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2 votes
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Making sense of the Jeans mass

The Jeans mass, given by $M_J=\sqrt{\left(\frac{-5k_BT}{Gm}\right)^3\cdot\left(\frac{3}{4\pi\rho}\right)}$, is the threshold mass a dust cloud must have in order to begin gravitationally collapsing ...
AlanFox86's user avatar
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What’s the minimum mass required for a star to burn helium?

What’s the minimum mass required for a star to burn helium? I’ve liked online but I’ve gotten inconsistent answers.
blademan9999's user avatar
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Difference between star formation rate and star formation history

When we speak about galaxies evolution, what is the difference between the star formation rate and the star formation history?
Daniele Zambetti's user avatar
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Time of collapse of stellar dust cloud

A stellar gas cloud collapses onto itself once it reaches Jean's mass, and the time it takes for said cloud to collapse is given by: $t_{coll}=\sqrt{\frac{3\pi}{32G\rho_0}}$, where $\rho_0$ is the ...
AlanFox86's user avatar
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Dynamical instability and thermal instability

I'm studying instability in Stellar Dynamics (in particular globular clusters instabilities). I have not understood clearly the definition of these concept. Dynamical instability is the study of the ...
nervousdog's user avatar
3 votes
1 answer
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How many type II supernovae are there per stellar mass formed?

I have been searching for the number of type II (core-collapse) supernovae per unit of stellar mass formed. It is my understanding that a star must have an initial mass of at least 8 times and no more ...
sav's user avatar
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3 answers
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How line of sight is determined?

How do they calculate the line of sight of a galaxy or binary star system from an observer's point of view. the velocity of a star in a binary star system depends on the line of sight so how do they ...
starwatcher_65's user avatar
1 vote
1 answer
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Numerical Integration for White Dwarf Model [closed]

I'm creating a numerical integration model of a white dwarf. So I've started with calculating electron pressure vs number density across a wide range of values. Using the equations of state in ...
Celina Emma's user avatar
1 vote
2 answers
136 views

Star with quadrupole in binary system violates Newton's 3th law?

Suppose that, in a binary system of two stars, the star A (and only the star A) has a non-zero quadrupole moment $Q_A$. Then, the star B feels the usual gravity force plus an additional force, ...
gravitone123's user avatar
8 votes
2 answers
712 views

At what distance can I assume peculiar velocity is negligible compared to expansion velocity, to use Hubble's law?

I am working on a high school physics assignment and am trying to figure out a method to determine if the star is a giant or main sequence from its spectral and photometric data (from SDSS). I picked ...
Hossam Dahshan's user avatar
9 votes
2 answers
1k views

Why don't less massive stars explode in form of supernovas?

I'm a high school student with a question about supernovas and the life cycle of stars. I understand that supernovas occur in massive stars when they run out of fuel and collapse, resulting in a ...
Authentic Melody's user avatar
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The role of gas pressure in the life cycle of stars

As a high school student, I am curious about the significance of gas pressure in the life cycle of a star. While I have read about the radiation pressure and the pressure caused by the energy released ...
Authentic Melody's user avatar
3 votes
1 answer
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Color temperature or effective temperature?

I am a high school student interested in astronomy and physics, and I am trying to understand the difference between color temperature and effective temperature of a star. As I have searched this ...
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