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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The shape of stars that have anti-gravity [closed]

When a star has a negative acceleration, what will it look like? Can it get a spherical shape?
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Photons from stars--how do they fill in such large angular distances?

It would seem that far-away stars are at such a distance that I should be able to take a step to the side and not have the star's photons hit my eye. How do stars release so many photons to fill in ...
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Would a human body flying into the sun extend or decrease the time the sun is undergoing fusion? [duplicate]

Obviously 1 human body is... nothing compared to the sun, so if the question is easier to answer with 1 million, 1 billion, the entire human population that has passed away in history... the amount ...
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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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What is the difference between: Chandrashekhar limit and Schwarzchild radius?

I want a qualitative difference between the Chandrashekhar limit and Schwarzchild radius. They both pretty much look like the same thing.
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Why do they say universe will become cold with expansion?

The Universe is expanding and they say it will eventually become cold, and new star formation will stop. But galaxies are only moving away from each other, and each galaxy itself stays intact and the ...
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Don't we know how the magnetic field of the Sun is created? [closed]

This is how Wikipedia explains stellar magnetic fields: Stellar magnetic fields, according to solar dynamo theory, are caused within the convective zone of the star. The convective circulation of ...
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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 ...
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Why aren't the hottest stars mostly invisible due to radiating mostly in ultra-violet? [duplicate]

The hottest stars have surface temperatures in the range of 40,000K. Wolfram Alpha says that such a star acting as a black body should radiate almost no energy in the visible spectrum. Why then do ...
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Age determination of stars

In the report 'New observations of the most distant galaxies close in on cosmic dawn', an astronomer states: 'Using a well-understood age indicator based on the amount of hydrogen absorption seen in ...
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Does the Virial Theorem apply to degenerate matter?

I am trying to understand how the degenerated He core progressively increases its temperature as the star moves up through the Red Giant Branch. A well-known property of the degenerate He core is ...
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Nucleosynthesis: other than big bang and supernova

According to many texts, hydrogen, helium and traces of lithium-7 were created in a brief period after the big bang; helium is created through fusion (pp, CNO) in main sequence stars; elements like ...
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May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again?

May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again? My question is not about would that explosion leave a neutron star as a remnant but ...
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What is the heaviest element being produced in Sun?

Helium is being produced currently in Sun. 3 questions. Other than Helium what other elements are currently being produced in Sun right now.? Looks like in 5 billion years, when Sun will become a ...
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Why don't absorption and emission lines cancel out in our Sun?

I was looking at this answer on why absorption lines and emission lines don't cancel out: An experiment shining light on the material and looking at the reflected spectrum will see absorption ...
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Are the physical structures in our sun of comparable complexity to those in the human brain? [closed]

The writings of Rupert Sheldrake tend to provoke strong emotions, be they ridicule, curiosity, outrage, sympathy, disgust, or otherwise. While Physics SE is not an appropriate forum in which either to ...
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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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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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Why will the increase in the sun's luminosity accelerate with respect to time?

From http://en.wikipedia.org/wiki/Future_of_the_Earth#Solar_evolution At present, nearly half the hydrogen at the core has been consumed, with the remainder of the atoms consisting primarily of ...
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How to find transverse component of star's velocity given its proper motion and distance from observation point?

If $\mu$ is the proper motion of a star in arcseconds per year, and $d$ is the star’s distance from us, then the transverse speed, $v_t$ will be $$v_t=d\sin\mu$$ For small motions (assumed for ...
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How are we able to observe Fraunhofer lines in a star's spectrum?

How is it possible to observe Fraunhofer lines in the emission spectrum of any star, since the elements absorbing the radiation couldn't possibly absorb all the radiation corresponding to a particular ...
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Rotational energy of stellar remnants

The theoretical maximum rotational energy a black-hole can have is 29% of its rest mass. We've often observed remnant black-holes spinning at nearly the speed of light. From this we conclude that ...
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The metric exterior of a massive object

The only condition apart from perfect spherical symmetry that is required for the retrieval of the Schwarzschild-metric $g_{ik}$ is actually ($R_{ik}$ being the Ricci tensor, the contraction of the ...
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Different width of spectral lines for different groups of stars

As seen in an HR-diagram, a certain stellar classification can correspond to more than one group/sequence of stars (G5 could for instance be either a giant, main sequence star or a white dwarf and so ...
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What is the distribution of Population I and II stars in the Milky Way galaxy?

I have been trying to find out the distribution of Population I and II stars in the Milky Way. The distribution I mean is the percentage of each population to the total stars in the galaxy. So in ...
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How can the mass of the sun be determined without using Kepler's law or gravitational lensing?

Can the mass of the sun be determined using the abundance of elements or alternative methods? It would be better to ask the question like this if we assume that I have an object that contains baryonic ...
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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" ...
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Does a star's emitted energy equal the work of its gravitational field?

Based on the formula of this question, it is possible to estimate the difference of the Sun's gravitational potential energy now and after it becomes a white dwarf. $$\Delta E = GM^2\left (\frac{1}{r_{...
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Star formation confusion

If gravity is really a weak force compared to other forces, then how does gravity pull hydrogen atoms in a nebula to from stars. I understand that hydrogen is in atomic or in the molecular state in ...
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Is it possible for the Oort cloud to account for the Dark Matter issue?

I'm no cosmotolicist, so forgive me if I'm completely off the mark here. I'm just a curious observer. A few years back, I read that there is not enough matter in the universe to account for the ...
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A violation of energy conservation?

Imagine a universe which contains a single sun and nothing else. The sum of the energy of the univese is then simply the energy contained in the sun and the photons it emits. If I have a theoretical ...
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If planet like Jupiter is massive enough to hold hydrogen with its gravity is it bound to become a star?

I have been reading about Jupiter as of late and reason I am asking is if Jupiter has strong enough gravity to pull hydrogen to itself then it should be only matter of time when it will acquire enough ...
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HD 140283 and the age of universe

I am watching a video on a star that is supposedly older than the universe. HD140283 (Methuselah). According to the first 20 years of research on the star, scientists believed the star is just over ...
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Why is Big Bang Nucleosynthesis favored over Stellar Nucleosynthesis?

We know that a hot soup of plasma as it cools (as space expands) can produce light elements if the baryon-photon ratio is just right and the space expands quickly enough so that the neutrons and ...
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Oldest population 1 star system?

While reading Stanislaw Lem's essays on advanced civilizations, I had a question: When did the earliest generation of population 1 star systems form? How much older could they reasonably be than our ...
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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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What are the conditions for a clean night sky? With plenty stars? [duplicate]

You know.. at some places of Earth, the night sky looks like this: (right?) However, you might definitely know that, at some other places, the night sky looks like this: (source: themarkeworld.com) ...
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How is the parallax angle actually measured?

I understand that parallax is used to measure distances to stars. But how is the parallax angle actually measured? In the parallax diagram we have two similar triangles, but we don't know any values ...
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Strange conservation of energy in Navier-Stokes Equations

We want to roughly model the fluid flow of a star; consider the following proposition: In the absence of viscosity, and heat conduction, the Navier-Stokes Equations for a steady, spherically symmetric,...
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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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What reduces the efficiency of galaxy formation at lower and higher masses?

What reduces the efficiency of galaxy formation at lower and higher masses? (Feedback mechanisms) I understand its something to do with supernova feedback and AGN feedback but I can't seem to ...
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What would happen if all protons in the Sun had a charge of 1.000001 times the elementary charge?

The whole sun would be positively charge, but would it explode because of it? Or would it just expand a bit?
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Will energy ever run out? [closed]

Gravity is the source of all energy and it will never go away. So that means there will always be energy for us right? I have seen some places say that energy will go away eventually and the last star ...
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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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Expressions for emitted and incident flux of a star confusion

The physical flux is the total energy flowing across the unit area from all directions: We can write flux as a function of intensity as follows: $$F = \int_0^{2\pi}\!\!\! \int_0^{\pi} I \cos(\theta) \...
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How to correct the Schwarzschild metric in the presence of Dyson sphere?

I was solving a problem in general relativity about Dyson sphere around a star. I don't have any problem solving the problem but in the question Dyson sphere was assumed to be massless. I checked ...
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Lane-Emden Solutions Near the Origin

I am trying to understand from class how to get anything past $1-\frac{1}{6}\xi^2$, $n=0$. Since my lectures state that it is solved in a series as shown below: $\Theta(\xi)=\sum_{i=0}^{\infty}a_{i}\...
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What is the process of star formation? [closed]

What is the process of star formation and what happens to stars after their death?
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Where do brown dwarfs get deuterium from?

Brown dwarfs don't have a high enough temperature to begin fusing hydrogen, but they can fuse deuterium or burn lithium, according to Wikipedia. Where do they get the deuterium from? Is there just ...

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