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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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Can a star visually look like a black hole? [duplicate]

Amateur question incoming so please bear with me. Assumptions If a black hole is born from a star going supernova, intuitively it should have the same or less mass compared to the star. Black holes ...
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What percentage of stars are giants/subgiants/main sequence etc

I am trying to find the percentage of main-sequence stars along with red-dwarf percentage for my research paper. I did find one article regarding, however it is very old and i require recent data ...
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Is the Universe an isolated system? [duplicate]

I am not a physicist but this question has bugged me for a while now. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. However, if the ...
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How is it possible to see stars-light, from stars millions of light years apart with the naked eye? [closed]

How is it possible for us to see stars that are millions of light years 'APART' from one another with the naked eye when we look at in the night sky from horizon to horizon? (i.e., pick any stars ...
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Energy budget of of proton-proton fusion (p-p chain)

How much energy is released in the first nuclear reaction of the p-p chain which produces energy in lower-mass stars like the Sun? The value of 1.44 MeV is given in many sources, but I don't ...
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Does a star need to be inside a galaxy?

Must a star belong to a galaxy, or could it be completely isolated? In case it can be isolated (not belong to a galaxy), could it have a planet orbiting around it?
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Event horizon and the existence of point particles

In this paper by David Kuap that first introduced the concept of Boson stars, he states that when the Einstein-Klein-Gordon system of equations is solved, the solutions obtained do not account for an ...
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45 views

How did Edwin Hubble estimate the velocity of distant stars?

I didn't know how to be succinct with my actual question in the title. My question is, how did he separate the components of the actual velocity of stars from that of the velocity due to recession (...
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Treating stars and planets as a blackbody determine the temperature of a planet that has EM radiation incident upon it from a star

Consider the following question: Power emitted by the star via the Stefan Boltzmann law is as follows: $$4\pi\sigma T_s^4 r_s^2 $$ However the power will drop over distance and so we can say that ...
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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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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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Do supernovae push neighboring stars outward?

I know that a supernova can mess up the heliosphere of nearby stars, but I'm wondering if it could physically push neighboring stars off their trajectories. It's fun to imagine all the stars ...
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Doubts about the formation of the bullet cluster

The bullet cluster is formed by the collision of two clusters of galaxies. After the collision, the stars and galaxies in those two clusters passed through each other. But the intergalactic gas clouds ...
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Forming a Neutron Star: inverse $\beta^-$ decay or electron capture?

There are three different kinds of beta decays: $\beta^-$: n $\rightarrow$ p + e$^-$ + $\overline{\nu}_{e^-}$ $\beta^+$: p $\rightarrow$ n + e$^+$ + $\nu_{e}$ electron capture: p + e$^-$ $\rightarrow$...
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Naive question about Gravitational collapse

Suppose that you have a probe orbting a $10M_{\odot}$ star in the final moments before gravitational collapse. In a time $t$ the collapse event occurs. So do you really would see all the matter "...
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Would a Dyson sphere face physical limits faced by white dwarves?

During a recent online discussion, one of the participants made the claim that a Dyson sphere would be limited in mass by the Chandrasekhar limit. Attempts to solicit evidence for this claim were ...
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Wildly Inconsistent Answers Re: A Teaspoon of Neutron Star versus the Giza Pyramid

I'm experiencing a mild fit of nerd-rage here and I'm hoping someone can help. I was watching a documentary and it made a claim I've heard a few times before: that a teaspoon of material from a ...
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1answer
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Was a black hole formed by only one star or many stars? And can a black hole be formed by other materials (non-stars).

Although I know that a black hole can be formed by gravitational collapse of a massive dead star, I'm not sure whether a black hole can be formed by collapse of many stars.
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Rayleigh Scattering and Red Giants

Rayleigh scattering is responsible for the color of the sky. Consider a planet with an atmospheric composition similar to Earth's but orbiting a red giant. Suppose further that the planet is in the ...
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2answers
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Nuclear Fusion Proton-Proton Chain

When hydrogen nuclei are able to overcome the coulomb forces, two protons collide. As a result, one of them decays into a neutron and a positron and electron neutrino are emitted. However, isn't mass ...
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Inferring Properties of Stars from Masses and Radii

I have two questions related to inferring properties of stars from their masses and radii. What properties of a star's spectrum could we deduce? In particular, do all stars emit like black bodies? ...
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1answer
38 views

Are all binary stars also variable stars?

Since variable stars are the once whose luminosity change according to our perception and all binary stars must go through eclipsing, Can we say that all binary stars are also variable stars?
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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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4answers
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Are there stars that wouldn't look white to the naked eye? [duplicate]

I have a small YouTube channel in which I make videos about topics relating science and things I find interesting. The topic I'm working on recently is on the color of the sun. What I thought at the ...
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1answer
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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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Why does the Sun appear more round while distant stars can appear more pointed?

In a minute physics video about the shapes of stars, it mentions that stars in the night sky appear star-shaped due to imperfections in our eyes known as suture lines which cause diffraction. Then ...
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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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Free-Fall time of a collapsing Star (Spherical Symmetry/No Rotation/Classical Mechanics) [closed]

I have been trying to prove the free-fall time $(\tau_\text{ff})$ of a collapsing star, which is the time it would take a star to collapse due to gravity, in the absence of pressure or other ...
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How can we see stars if their apparent width is less than a pixel?

Stars are so far away that their apparent width is essentially zero when compared to any pixel of a camera or TV screen. And yet we can still see them. According to our eyes stars have a finite ...
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Observe stars with a cloudy sky

Is there any way to view the stars even in a cloudy sky? For example by using a particular camera, or a particular UV filter in front of the camera, and so on.
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Difference between speed of sound into a star

I try to understand the following graphics with x-axis being the radius of a typical star : I would like to knwo if $\delta c/c$ represents the relative error between theorical and experimental ...
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4answers
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Is there any way looking at Stars from that I can understand that we are revolving around the Sun?(Not caring about other planets for now)

I am learning Astronomy. I videos or lessons I look at are already biased over heliocentric math to explain the parallax concept. I am looking for an intuition to get myself a deeper understanding of ...
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Why do our eyes perceive changes in apparent position of stars as twinkling?

Okay, so we all know that the changes in refractive index leads to continuous changes in star's apparent position but then why don't we see them moving up and down rather than brighten and dim in ...
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Why do black holes warp spacetime so much more than stars that have the same mass? [duplicate]

If I have a black hole with a mass that's exactly the same mass as a star, why does the black hole warp spacetime so much more (light can’t escape) than a star (light can escape) with the exact same ...
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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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Is there evidence of gas ever forming a black hole without being a star first?

Here's my general understanding of how gas particles form a black hole: 1) Gravity pushes gas particles together. 2) These fast particles create heat (from friction due to them rubbing together?). ...
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If a star forms, entropy decreases… but doesn't this require some form of energy?

A cloud of matter has high entropy. In order to form a star out of matter, the entropy must decrease. For this, energy is necessary. Where does this energy come from?
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Why does a star with its core collapsing and about to undergo a supernova, explode, instead of rapidly collapsing all of its matter into a black hole? [duplicate]

I am guessing this has something to do with density. I would assume that a massive star that has its core collapsing would be a prime candidate for having its core turn into a black-hole. If the ...
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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
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Why have all stars roughly the same order of surface temperature?

Given that stars vary in volume over 10+ orders of magnitude, why are they roughly the same order of surface temperature (emitting much of their radiant energy in the visual range of the EM spectrum)? ...
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What determines the surface temperature of the sun?

The core temperature of the sun is on the order of 15 million degrees kelvin while its surface temperature is around 6000k. What are the main factors which determine the surface temperature of the ...
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1answer
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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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1answer
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How accurately can the distance of a star be measured?

With the launch of the GAIA mission some years ago, a new precedent was set in mankind's ability to map our universe. However, how accurate are the distances created by this? From ESA's website, I ...
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Age-metallicity-extinction-redshift degeneracy

I'm studying astronomy and astrophysics (particularly Star Formation) and I ran into a problem. There is this mention of the age-metallicity-extinction-redshift degeneracy which I don't quite ...
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3answers
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What color are stars?

I know that the sun looks white to us because it emits a large variety of color, making it appear white to our eyes but does this mean that all stars emit a variety of light? If so, then how can we ...
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Magnitude of the faintest star visible to the human eye? [closed]

Hipparcus said the faintest magnitude of a star the human eye can see is 6. How can one mathematically verify this? So far: Assumptions: Human eye receives $1000 \,\mathrm{photons/(cm^2 \, ...
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2answers
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Gravity/Energy relationship

I understand that gravity is not energy, but is force, but my question revolves around if the presence of gravity in the universe results in a continuous amount of energy, from gravity-induced ...
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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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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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How can S-factor be masured directly in a star?

The astrophysical S-factor is defined as $$S(E)=E\exp(2\pi\eta)\sigma(E)\,,$$ with $\sigma(E)$ the cross section and $\eta$ the Sommerfeld parameter defined as $$\eta=\frac{Z_1Z_2e^2}{\hbar}\sqrt{\...