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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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111 views

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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28 views

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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90 views

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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32 views

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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43 views

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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169 views

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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100 views

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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39 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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66 views

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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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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53 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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102 views

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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193 views

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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104 views

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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121 views

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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63 views

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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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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172 views

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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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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838 views

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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56 views

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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255 views

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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92 views

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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140 views

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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134 views

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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124 views

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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28 views

Estimating the reddening of a star? [closed]

I'm stuck on a question concerning how to estimate the reddening of a star. The question is: "A star near the Galactic plane has observed apparent magnitudes in the blue and visual bands of $B = 15....
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265 views

How does gravity cause nuclear fusion in stars?

I am a bit confused regarding the nuclear fusion that occurs during star formation. For example, suppose there is a huge hydrogen cloud. It gets more mass and therefore pulls in more and more hydrogen,...
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55 views

Why does hydrogen fuse in a star? [duplicate]

I have only had basic classroom experience with physics but I have done a lot of research on my own and I am wondering why a newly formed star or any planetary body composed purely of hydrogen will ...
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4answers
225 views

Energy Transport in stars

I'm trying to understand why convection is an efficient mode of energy transport in the outer layers of the solar interior. Could anyone give me a little bit of knowledge?
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80 views

How much of Sun's mass is “regular” matter? How precisely do we know Sun's composition?

This is a question which spun of this Can the Sun / Earth have a dark matter core? I have argued that it is possible to pretty accurately estimate how much mass of Sun is in the regular matter, so ...
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Can the Sun / Earth have a dark matter core?

If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest. Hence we have papers about neutron stars possibly containing dark matter cores (...
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70 views

Will changing the Barycenter change stars orbits?

A barycenter of a galaxy is the "balancing point" of it where every object inside the galaxy orbits. With this information, if somehow (I don't know how, maybe you can give me a way in your answer) ...
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133 views

Orbits of stars in the Milky Way

I know that in our Solar System, planets orbit the Sun according to Kepler's laws. What about other stars in the galaxy? Does each type of star population (e.g. population I and II) have a certain ...
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408 views

A joke on the Doppler effect: does this make sense? [closed]

I'm currently writing something that explores the phenomenon of inside jokes, in which I use an astrophysicist joke that is meant to be undecipherable to the average reader. It was recommended to me ...
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128 views

What is the local stellar number density?

Is it just me or does this paper, while providing a great equation for the behaviour of the general stellar number density, never actually give a value for the local stellar number density $\rho(R={\...
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82 views

How long would it take for the solar core to destroy Earth? [duplicate]

If Earth were at the middle of the solar core, how long would it take to destroy the planet? Furthermore, how would the planet be destroyed? To consider the planet to be destroyed, it must be ripped ...
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79 views

What is the simplest way to find the distance of stars?

Once, I was staring at the sky and wanted to know the distance to stars I could see. I searched the Internet but didn't find any easy to use tools. The distance to stars can be measured using ...
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172 views

Why space is dark? [duplicate]

There are trillions of stars like the Sun in our universe so "why is it space is dark and cool?" Well I really meant that our stars, giant balls of gases which exist by expelling huge amount of energy ...
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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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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 ...