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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Adiabatic equation of state for a star

I am a little confused. To describe stars the adiabatic equation is often used: P = k$\rho^{\gamma}$. For a monatomic gas, the following holds: $\gamma = \frac{5}{3}$. However, since the sun is not ...
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Would a star collapse if surrounded entirely by gravitationally-bound mirrors? [closed]

As the mirrors reflect the light back at the star, the star will become denser. As the mirrors keep falling towards the star, the amount of pressure that can be reflected back increases. Is this ...
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What's the lifespan of Deuterium and Helium-3 in the Sun?

What's the lifespan of Deuterium and Helium-3 in the sun? How long on average, the Deuterium and Helium-3 atoms last in the Sun's core?
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How big would a star made of pure deuterium have to be to start fusion?

D-D fusion happens much more easily than proton-proton fusion, so I imagine a star made of pure deuterium could be much smaller and still have fusion. Are precise size limits known? How does having a ...
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What happens to the matter already at the very center of the star when it turns to a black hole?

I was wondering whether when an object collapses into a black hole, the matter in the position $r=0$, instantly becomes part of the singularity, or does it take time to fall into the singularity, and ...
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Why do elliptical galaxies not have large proportion of blue stars?

In an article it was given that elliptical galaxies are also formed when a spiral galaxy experiences continuous star burst thus depleting it's gas. So if this is correct than why do elliptical ...
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Thermodynamic ensemble of Stars instead of molecules

If we take an enormous amount of molecules (an ensemble), the laws of statistical thermodynamics become valid: we can use them to make predictions of the macroscopic behavior of the ensemble. I was ...
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How much energy from neutrinos does a Helium flash create?

How much energy from neutrinos is given of by a solar mass star when it undergoes a Helium flash?
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What is the difference in time rates between the volumes where fusion takes place in a star vs outside observers like ships orbiting the star?

I have found information suggesting the difference between the surface and the center isn't even worth worrying about, but since we needed GR to account for Mercury's orbit, I can't help but wonder ...
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Too many low redshift galaxies in NED database

When using the NED database I found there are too many galaxies with very low redshift (Near zero). I used NEDs search by parameters function to find all galaxies within Z=0 to Z=.03 redshift. I did ...
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What is ohmic decay and why does it happen in magnetized celestial bodies like stars and pulsars?

I've seen term "ohmic decay" mentioned in several papers (example) regarding the decay of magnetic fields in celestial bodies like planets, stars, and pulsars, but I can't seem find a clear ...
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Why space telescopes images show diffraction spikes around stars, but not galaxies?

I've seen this tweet recently: https://twitter.com/ThePlanetaryGuy/status/1544801752893067265 Additionally to the image, where it's pretty clear, the post says: Stars are six-pointed; everything else ...
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Is there a maximum mass limit for black holes?

We all knows that neutron star and a black hole is a final end stage of a giant stars, and neutron stars can also become a black hole, we also knows that minimum mass limit for stars to become a ...
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How can find recombination coefficient of hydrogen in various stars

I'm trying to calculate recombination coefficient of hydrogen at different temperatures in various stars. How can I calculate it at different temperatures?
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Evolution into a main sequence star

I was reading the following from the textbook An Introduction to Modern Astrophysics by Bradley W. Carroll Dale A. Ostlie, "Due to the onset of the highly temperature-dependent CNO reactions, a ...
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Is it possible to determine the distance between the earth and a star by only studying the light emitted from this star?

I was reading about the Doppler shift and how we can measure how fast something is moving through its Doppler shift. This got me thinking is their a way/formula to measure the distance between us and ...
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Can Jupiter turn into a star if it radiated off enough heat?

Since a star heats up when it radiates more heat (via gravitational compression), and since that's also how protostars turn into stars, I was wondering what are the chances of Jupiter reaching the ...
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Is it possible to visualise red shift?

If a picture of a star or galaxy hurtling away from Earth is taken, does it appear red despite it being a different colour? Would a blue coloured star moving away from us appear red to us or vice ...
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Which type of star is most effective for solar power?

I'm working on a worldbuilding game, and the subject of stars has come up. Imagine you're a species, chilling in the Goldilocks zone of some alien planet, orbiting an alien star. Your people stumble ...
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In view of the frozen flux theorem, why don't stars have much stronger magnetic fields?

According to the frozen flux theorem or Alfvén's theorem, the magnetic field in a plasma is frozen into the plasma and must move along with it. That is, in an ideal plasma, the magnetic flux through ...
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What would happen to a star caught in the path of an astrophysical jet?

The question pretty much captures it. What would happen to a star caught in the path of an astrophysical jet? I imagine the distance to the source of the jet, and the power of the source, matter most ...
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Could anything ever be brighter than the sun in our sky?

Is there anything that could explode or exist that would appear brighter than the sun in our sky? There was that meteor in Russia in 2013 where it appears brighter than the sun. However, is there a ...
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Colours of the sky if sun was blue?

What would be the colours of the sky at different points of the day if the sun was a blue star? This is assuming that our earth is at a similar distance away from the surface of the blue sun as it is ...
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Fusion Rate and Luminosity in Stellar Model

In astrophysics textbooks one of the differential equations to solve in stellar model is $$\frac{dL}{dr}=4\pi r^2 \epsilon$$ where $L(r)$ and $\epsilon (r)$ are the luminosity and fusion rate per unit ...
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Are we totally limited to the Milky Way for all stellar astrophysics?

Simply put; Are we able to make any observations of the individual stars in other galaxies? Is the depth of our scientific knowledge on star systems, based solely on stars in the Milky Way Galaxy ...
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On the Critical Angular Velocity of Stars

I read on Wikipedia that if the Angular Velocity of a star is above its Critical Angular Velocity, it reaches hydrostatic equilibrium in the shape of a Jacobi Ellipsoid. But how exactly would I find ...
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Relationship between mean absolute Magnitude and mean luminosity in cepheid variability

"When a stellar population 1 star with a mass of 3-10 M(sun) evolves into pulsation variability that periodically repeats contraction and expansion, there is a proportional relationship between ...
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How do you estimate the core temperature of a star?

Given a star's mass, radius and average composition (e.g. 90% H, 10% He), is there a formula to estimate the core temperature of that star? I only found one for a lower bound but that wasn't very ...
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Why is the bound-free opacity proportional to $Z$?

I've seen the following formula repeated in multiple places, including wikipedia that the bound-free opacity is proportional to the metalicity $Z$ $$ \kappa\approx 4.34\times 10^{25}\frac{g_{bf}}{t}Z(...
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Rosseland mean of the free-free opacity in terms of fundamental constants

I'm currently trying to compute the Rosseland mean of the free-free opacity but am consistently off by a numerical factor. To keep things simple, we will take the non-relativistic limit, and roughly ...
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How do astronomers calculate the mass of celestial bodies light year from Earth?

I have read in many scientific stuff that mass of this planet or that stars is about '$n$' times the mass of Sun. I have gone through many websites and videos on YouTube but didn't find the right ...
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Would a head-on collision between two stars create heavier elements?

I was thinking about Przybylski's Star, and I was wondering how it was possible that so many heavy elements ended up in the star, such as einsteinium, californium, berkelium, etc. But there is ...
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Doubt regarding the positioning of starshade in new world's mission of Nasa

The new worlds mission of NASA has an occulter with the telescope, Why did they place the occulter at a distance instead of attaching it to the telescope such that there is a hole as big as the size ...
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Confusion with light year distance and space events

I had read that the Betelguese star may be going supernova in may of 2022. Now it is about 500 Light years away, so if we see a supernova explosion in may, then does that mean it occurred about 500 ...
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How to calculate change in absolute magnitude by a change in stellar radius?

Suppose that the radius of a star increases by some factor, how does this affect the absolute magntiude of the star? I know that $M_1 - M_2 = \Delta M = 2.5 log \frac{L_1}{L_2}$ so if I knew the ...
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Black-body radiation and visible spectrum of stars

I've done some reading on black bodies and black body radiation, after reading that stars are considered black bodies. As such I think the black bodies absorb all light, but also put off a radiation ...
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How small/large can a sun/star be?

I have zero knowledge about astronomy (I often mistake it with astrology) so my question might be a bit naïve. But what are the limits for stars to be stable? I guess you can't up or downscale our ...
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Why are galaxies much closer spaced (relative to their size) than stars?

I have read this question: So the average spacing is somewhere in the range of 10 - 100 times the size of the biggest galaxies. The peas I had for lunch today were (at a guess - I didn't measure them!...
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Doppler Effect of Stars

To measure the velocity of a star (away from us), we use its Doppler redshift. However, a redshift may be a result of other factors, such as different gravitational potential (which is always the case,...
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Forbidden emission lines [OI] in HerbigAe/Be

I am a beginer in astrophisics and I am studying HerbigAe/Be stars. I have read that this kind of stars have a circumstelar disc that emits in the infrared and that some of them presents emission ...
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How close could a 1 solar mass star get to our solar system without disrupting the planets' orbits

Is there an easy way to calculate how close a star of given mass could get to our solar system without disrupting the orbits of the planets? Just looking for a rough estimate, nothing too involved
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How is the CNO cycle able to occur in main sequence stars if they only fuse hydrogen into helium?

From what I understand, main sequence stars only fuse Hydrogen into Helium, and this is mainly due to the proton-proton chain or the CNO cycle. However, the CNO cycle requires a carbon catalyst. If ...
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What is the formula to calculate the parallax angle?

The images were rendered in Blender. The two images were rendered 20 meters apart, side by side. The focal length is 50 mm if that matters. What is the formula to calculate the parallax angle θ as ...
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Can you explain this line from "A brief history of time"?

Newton realized that, according to his theory of gravity the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point? ...
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Why can we determine the temperature of the star looking on its spectrum?

For example, I have this spectrum: So, looking at it how can one tell the temperature of the star? the y-axis is intensity? flamda? I assume we can use wavelength to tell, but without calculations ...
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What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?

What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions? To my understanding these are the two sources of luminosity for a star, so I'm ...
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If space is a vacuum, how do stars form?

According to what I have read, stars are formed due to the accumulation of gas and dust, which collapses due to gravity and starts to form stars. But then, if space is a vacuum, what is that gas that ...
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Why is there no stars made of bosons?

Consider the white dwarf (or similarly neutron stars), which can be modeled as a star made of degenerate Fermi gas: A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed ...
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What is the difference between free-fall timescale and dynamical timescale?

I have encountered these terms quite often in astronomical textbooks, and sometimes they are used interchangeably. I have also heard that the free fall timescale is larger than dynamical timescale. ...
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Can a photon lose all of its energy due to gravitational redshift?

Imagine a photon that is emitted by a star that is at infinity with respect to me. We can observe the gravitational redshift happening to that photon with respect to my reference frame. I was ...

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