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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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1answer
113 views

Can a star reflect light from another star? (Enough for it to be visible)

Suppose a binary star system has relatively a dim red star (such as a red giant or red dwarf) and a very bright blue star. From standing on a planet much closer to the red star, would it be possible ...
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203 views

Mass Luminosity Relation Review

I have read that exists a relation between the luminosity and the mass of a star $$\frac{L}{L_\odot}=\left(\frac{M}{M_\odot}\right)^a$$ with $a$ depending on the mass $M$. I have looked for a ...
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Can there be a black hole as big as the space between any two neighbor stars?

Can there be a black hole as big as the space between any to neighbor stars? e.g. lets say we Proxima Centauri/Alpha Centauri A and our Sun. The distance would be about 40,208,000,000,000 km. So ...
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69 views

Does the circumference of light from a star expand?

If photons do not split, and light travels in straight lines then at x distance from a star there should be gaps in the straight line light tangents (which would make the star unobservable) However ...
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1answer
41 views

Simplified formula for temperature between the star and background temperature

I am looking for a simplified formula to calculate the temperature of an object in space and how distance from the star affects said temperature. Something that closely represents reality will ...
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76 views

Celestial Body Approaching Speed of Light, “Observed” as a Black Ellipsoid?

I have an interesting question, one which I think may not work haha, but please bear with me. Let's work with our sun, with mass of about $2 \times10^{30}$ kg. According to the following formula, ...
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1answer
109 views

How do scientists tell us the mass and size of planets and stars $20\,{\rm ly}$ or more away?

I was just watching a scientist discussing an Earth-like planet in another solar system. He had many facts to share about it, such as that it is $20\,{\rm ly}$ from our Sun, $20\%$ larger than Earth ...
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2answers
196 views

Is it possible for liquid metallic hydrogen to be present in a star

Liquid metallic hydrogen can form at extreme temperatures and pressures like that in the center of Jupiter and Saturn. I was just curious since some of the conditions can occur on stars is it ...
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Does the associated colour of a spectral class (red and class M, for example) come from the peak black body radiation of stars in that class?

Each spectral class O through to M has an associated colour. Class O stars are described as blue stars, for example. Is this colour determined by the peak wavelength of their black body radiation? Do ...
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58 views

Does anyone know where or how I can find a list of catalogue/list/paper of 100,000 brightest stars?

Anything above 10,000 is good however, I am only interested in the brightest ones seen from earth. Any simple projects for collaboration between astrophysicist and robotics student?
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A star with its radius not much larger than its Schwarzschild radius

I was asked about the question today: suppose that you are observing from afar a spherically symmetric star of mass $M$. Its radius $R$ is $\textbf{not}$ much larger than its Schwarzschild radius. ...
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Photons & Space [duplicate]

If a star emits endless streams of light photons in all directions why is it that we have any darkness? Yes light can be absorbed by objects and transition into other particles but from its foundation ...
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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: Have you seen any stars from ...
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79 views

What does a redder galaxy mean?

I've been reading on the subject and I've repeatedly read that red galaxies are those with redder stellar populations which means (according to my readings) older star populations, with low star ...
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206 views

The PPI Chain is composed of 3 steps: Does only the 2nd step release energy?

The PPI chain is \begin{align} \rm\ ^1H + {}^1H &\rm\rightarrow {}^2D + e^+ + \nu_e \tag 1 \\ \rm\ ^2D + {}^1H &\rm\rightarrow {}^3He + \gamma \tag 2 \\ \rm\ ^3He + {}^3He &\rm\rightarrow {...
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1answer
130 views

Were the 1st generation stars low or high-mass stars?

I have been taught that the first stars to be "born" could not use the CNO cycle to fuse Hydrogen into Helium as there were no elements heavier than Helium and a bit of Lithium to use in those ...
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What happens when stars in an elliptical galaxy collide?

I don't mean when stars in a binary system spiral in and fuse together. I mean when they undergo a fast head on collision in an elliptical galaxy. I assume it's much rarer for stars to undergo that ...
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Why does the H-burning Shell do the CNO cycle instead of the PP Chain?

A star that initially produces energy through the PP Chain will eventually exhaust its Hydrogen leading to a core contraction in order to increase the temperature to generate again nuclear reactions. ...
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1answer
218 views

What is the Rosseland mean opacity a function of?

For a given star, (if anything) what is the Rosseland mean opacity a function of? For example, does it depend on distance from the center?
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Why $\rm He^{++}$ is more opaque than $\rm He^{+}$ and so absorbs more energy?

In the Cepheids, $\rm He^{++}$ is more opaque than $\rm He^{+}$ so it absorbs more energy. If it is because a more charged particle have a higher electromagnetic field and the stronger the field, the ...
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101 views

How can we evaluate the ratio of abundance of Carbon to Li, Be and B?

In stars' nuclear processes, if the triple $\alpha$ reaction explain why Carbon is much more abundant than Li, Be, B, how can we evaluate the ration of abundance to ~$10^5$ times ? Is it possible to ...
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217 views

How does the collision of two protons forming a hydrogen-2 atom produce energy if a neutron is more massive than a proton?

Wouldn't the transformation of a proton to a neutron require energy since the neutron is more massive?
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Ways to make a star go supernova? [closed]

Asking for a fictional storyline. Say a type iii civilisation on kardashev scale want to make a star go supernova. Then what are the possible ways to achieve this? The said star being massive ...
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Where will the Goldilocks zone be when the Sun becomes a red giant?

In about 5 billion years, when our Sun expands into a red giant making our planet uninhabitable, where will the new Goldilocks zone be? Could life form on a new planet in the Goldilocks zone? ...
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1answer
622 views

What is the difference between the Jeans mass and the Bonnor-Ebert mass?

It appears that they both describe the upper boundary mass that a cloud in space may inhibit before gravitational collapse. From Wikipedia, on Jeans mass/Jeans instability: "...Jeans instability ...
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2answers
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How the Hertzsprung-Russell Diagram allows us to calculate distance to stars

I understand how to interpret a H-R diagram, in the sense that I know that the upper right top corner is occupied by cool stars, but they are very luminous so they must be big; and the bottom left ...
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3answers
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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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1answer
65 views

Model to predict temperature of the Sun?

In a homework problem, we were to assume the Sun is a sphere with uniform density and use the hydrostatic equilibrium equation to compute the pressure at the center of the Sun? Upon doing this, I was ...
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1answer
225 views

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. A few years back, I read that there is not enough matter in the universe to account for the gravitational forces at play, ...
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37 views

Can a star emits laser? [duplicate]

I know if I pump enough energy to a bunch of electrons so that they are all in their excited states, then I can introduce some photons to start off a chain reaction resulting in simulated emission. ...
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0answers
253 views

Help with high-school investigation/experiment on astrophysics [closed]

I need to find multiple ideas for a physics investigation relating to astrophysics. The investigation is going to be like a lab report and must include data analysis and be maximum 2000 words. I have ...
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2answers
148 views

Invariant Speed of Light using Binary Stars and Tangential Velocity

So I was in class the other day and my professor mentioned that we can prove that light is invariant using a binary star system. His reasoning: Assume a binary star system 1000-light years away from ...
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2answers
91 views

About light in the universe [duplicate]

As a light source in the universe (e.g. sun) emits light in different directions, some of the light emitted reaches places like Earth, and some doesn't. So does the light that reaches the Earth ...
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0answers
78 views

Why can gold only form in outer space? [duplicate]

I was reading an article by two Harvard Astrophysicists, which mentioned the following: "We value gold for many reasons: its beauty, its usefulness as jewelry, and its rarity. Gold is rare on Earth ...
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1answer
48 views

Potential of a Star at infinity

I just started physics research. I am learning about stars. My research adviser told me that the potential should be positive for large r then goes to 0 at infinity so the stationary point at ...
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2answers
138 views

Why the He core gets hotter and hotter? Is it because it shrinks?

I know that after a star in the main sequence runs out of H in the core, it will start burning H in the shells surrounding the (now) He core. (1) Why now the Hydrogen shells are hot enough for ...
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38 views

Book about the sun or stars in general

I would be interested to know if there are any popular science books on what we know about the physics and processes in our sun. It may possibly be a book about stars in general, but since in recent ...
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1answer
142 views

If Proxima Centauri is only 4.25 light years away, why is there no attempt at communication? [closed]

It is known that the Proxima Centauri star system is merely $\approx 4.25$ light years away from Earth. Moreover, an Earth-like planet has been discovered around Proxima B that is within the habitable ...
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1answer
36 views

Smallest star radius by loss (or production) of heat

I'm looking for the smallest possible theoretical size for a spherical uniform star in rotation, after it loses some energy as heat. I'm puzzled by the following calculations. Initially, the star ...
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2answers
48 views

Can something intervene between starlight and planet?

Let's say there is a HUGE orbit for planet x, and somewhere in the orbit, there are some debris or clouds or anything else. Can any of these block the light and stop it from reaching the planet x? ...
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2answers
84 views

Hertzsprung–Russell Axes

Why is the temperature axis of the Hertzsprung–Russell graph increased from right to left? Is it to do with polynomial proportionality?
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1answer
89 views

Why isn't the universe lit up? [duplicate]

Sun the sun and many other stars shine their light outwardly, and light travels very long distances, why is space dark? Why isn't it all lit up due to the stars?
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44 views

Red Giant Core Contration: How does it change the star's radius?

By how, I mean what is the equation. Context If the core of a red giant contracts the outer radius will expand; but I cannot find an equation that says this, but I have equations that say parts of ...
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1answer
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Why can't barium be produced in a supernova explosion?

In this video, Michael Merrifield claims that the elements barium, lanthanum and cerium cannot be produced within supernova explosions, and that they must be produced via a slower neutron-aggregation-...
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2answers
204 views

Can a “Solar System”-type system exist without a star or stellar remnant?

Since there can be planet-like astronomical objects that have larger masses than the Sun (for example an astronomical object with a large iron core), I'd think that there could be "Solar System"-type ...
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1answer
196 views

Four-velocity of a static, spherically-symmetric star

Let us assume the static, spherically-symmetric space time given by $$ds^2 = -e^{2\Phi(r)}dt^2+e^{2\Lambda(r)}dr^2+r^2d\theta^2+r^2\sin^2\theta\,d\phi^2.$$ For a static star, in which case the fluid ...
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98 views

Stars with same colour

This is the problem I'm trying to solve. When it says they have the same colour, does that mean that they have the same temperature?
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1answer
84 views

Can we define a sphere around us that would contain a star in any direction?

Can we find a radius R so that in any direction around us (earth), in straight line, we can find at least one star at a distance shorter than R ? If so, do we have an estimate ? Or do we know that ...
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3answers
287 views

Why are stars spherical whereas (some) galaxies are disks?

I read here that galaxies become disks if there is a lot of gas in them, since their angular momentum is conserved while their energy decreases due to collisions of the gas particle. I have two ...
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3answers
856 views

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 ...