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.
731
questions
8
votes
2
answers
751
views
Why don't less massive stars explode in form of supernovas?
I'm a high school student with a question about supernovas and the life cycle of stars. I understand that supernovas occur in massive stars when they run out of fuel and collapse, resulting in a ...
- 593
0
votes
0
answers
19
views
The role of gas pressure in the life cycle of stars
As a high school student, I am curious about the significance of gas pressure in the life cycle of a star. While I have read about the radiation pressure and the pressure caused by the energy released ...
- 593
3
votes
1
answer
49
views
Color temperature or effective temperature?
I am a high school student interested in astronomy and physics, and I am trying to understand the difference between color temperature and effective temperature of a star. As I have searched this ...
- 593
0
votes
2
answers
23
views
$y$-axis on HR diagram
I have an exercise where I have to determine the luminosity of a star with 10 000K. However, I'm confused about how to read off the $y$-axis on the graph when the scale is uneven. What is the function ...
- 63
1
vote
1
answer
15
views
Star equations of hydrostatic equilibrium for a mix of 2 fleebly interacting gases/fluids and interaction term
For a single matter species, the equations of hydrostatic equilibirum for a star are
\begin{eqnarray}
\nabla^2 \phi &=& 4\pi G \rho\\
\vec{\nabla} P + \rho \vec{\nabla}\phi &=&0
\end{...
- 172
0
votes
1
answer
52
views
Can I find the surface temperature of the Sun using a spectrometer?
So I have a high school physics project and I essentially have this experiment idea where I use spectroscopy to find the surface temperature of the sun. Now I'm essentially going to assume the Sun is ...
2
votes
2
answers
97
views
Can a massive star become a red giant more than once?
Massive stars may undergo multiple fusion processes as they near the end of their lifespans. Our sun will eventually start fusing helium in its inner core so that carbon is formed. As this occurs, the ...
- 319
3
votes
1
answer
40
views
Can the quark-gluon plasma of the very early universe be accurately characterized as a type of quark star?
The very early universe was dense and opaque. During the quark epoch, the entirety of the universe, up to every boundary, was a filled-in ball of QGP. Much like a star is a ball of ionized nuclei that ...
- 173
1
vote
1
answer
18
views
Should blue & white stars appear red and inflated while observed on the lower part of the night sky for the similar reason as the Sun during sunset?
Should blue and white stars appear red and inflated while observed on the lower part of the night sky for the fairly same reason as the sunlight during sunset? As these stars emit blue light ...
- 2,173
2
votes
1
answer
141
views
Is the temperature of the hottest star's core known?
WR 102 is believed to be the hottest star in the observable universe, whose surface temperature is $210,000 ^\circ K$. But the related wikipedia entry does not say anything about the temperature of ...
- 314
1
vote
0
answers
43
views
In a non-rotating sphere of fluid heated from the centre, what does the flow look like?
Consider a perfect sphere of fluid which is not rotating, is under the influence of its own gravity only, and is heated from the centre. What does the flow of fluid in the body look like?
In the ...
- 11
1
vote
0
answers
18
views
Stellar classification: Luminosity class
So in the astrophysics textbook by Carrol and Ostlie, when the luminosity class is discussed, it has such a sentence "The ratio of the strengths of two closely spaced lines is often employed to ...
- 141
0
votes
0
answers
26
views
Finding chemical equilibrium with an application to the Sun
Consider the following reversible reaction: $\rm H_{2}{\rightleftharpoons}2H$. To find chemical equilibrium, we use the chemical equilibrium constant. There are two equations for the chemical ...
- 23
14
votes
3
answers
3k
views
Is it possible to tell the difference between a young star that is just "big" and an older red giant?
I read the Wikipedia page for one of the biggest known stars, UY Scuti, and was curious to see the age of the star isn't really known at all.
When a star's hydrogen fuel is exhausted, it starts ...
- 243
1
vote
1
answer
56
views
What would the nucleus of a water planet be like?
If we have a planet made out of water, would it be all solid? What about the nucleus? Would it depend on the size of the planet?
- 141
0
votes
1
answer
75
views
How long will Brown Dwarfs live?
Brown Dwarfs are a technical star because of their masses. If Red Dwarfs live for 10 trillion years, then how long could Brown Dwarfs live?
2
votes
1
answer
92
views
Does the Sun increase entropy?
The Sun generates heat via fusion. The heat from this reaction gets distributed around the solar system and beyond. This process of spewing heat and radiation all over the place doesn't immediately ...
- 299
-1
votes
2
answers
59
views
Star gets eaten and spit out?
How does material get swallowed and torn apart by a black hole and have its light vanish. But somehow the same material escapes years later. After its light couldn't even escape?
They watched it for ...
5
votes
1
answer
27
views
Why is the common envelope ejected in some accretor-donor systems?
As an example, let us consider a binary system of a neutron star and an evolved star (e.g. red giant) that has expanded, filled its roche lobe, and started the mass transfer onto the neutron star.
...
- 95
3
votes
1
answer
313
views
Why are certain stars not moving in this timelapse video?
In this video, certain stars are not moving in the bottom left & top right corners. I thought only the pole star didn't move.
https://www.youtube.com/watch?v=QC8iQqtG0hg&ab_channel=...
3
votes
1
answer
71
views
Why is a star unstable if it's adiabatic exponents are less than 4/3?
In "Introduction to Stellar Structure" by Walter J. Maciel at page 76 it is said that for a partially ionized non degenerate hydrogen gas, the star is unstable if the adiabatic exponents are ...
1
vote
1
answer
17
views
Star convection gradient dependencies
In star convection you can work with radiative and adiabatic temperature gradients, that for example the radiative one can be defined as,
$$\nabla_{rad}=\frac{3\kappa L P}{16 \pi a c G m T^4}$$
This ...
- 479
0
votes
0
answers
31
views
Can starlight be described as a light beam?
I would like to study starlight propagating in the universe. Can I model the light as a beam with a radius $r$ and a unit wave vector $\hat {\mathbf k}$ with a frequency distribution $f(k)$? Also, the ...
- 85
2
votes
2
answers
53
views
What do these negative mass values obtained from the Lane-Emdem equation entail?
Starting from the hydrostatic equations for a star:
$$\frac{dM}{dr}=4\pi r^2\rho $$
$$\frac{dp}{dr}=-\frac{GM\rho}{r^2} $$
It is possible to obtain the following expression using the dimensionless ...
- 1,430
0
votes
0
answers
60
views
How is Starlight Reflected by Mirrors?
The chosen star is on the Z-axis of Mirror-A (Red). The Star image appears on the
face of this Mirror at the Origin of the CoSys.
Starlight Rays (Yellow lines) remain parallel, and do not diverge with ...
6
votes
1
answer
254
views
Why is lithium burned at lower temperatures than hydrogen inside stars?
The destruction of lithium inside stars through the reaction
$$ ^{7}_{3}{\rm Li} + {\rm p} \rightarrow 2\ ^{4}_{2}{\rm He}$$
takes place at just $\sim 3\times 10^6$ K.
This is much lower than the ...
- 122k
0
votes
0
answers
61
views
Calculate the solar central density using an equations of stellar structure
How can I calculate the solar central density $\rho_C = 150 \textrm{g cm}^{-3}$ using one of the equations of stellar structure like the the mass distribution equation $\frac{dM(r)}{dr}=4 \pi r^2 \rho(...
- 1
1
vote
0
answers
30
views
How can I calculate evolutionary timescales of low mass stars?
How can I calculate how long a star of a given mass will spend on an evolutionary branch before evolving off it?
I'm thinking about the evolution of low mass stars from the subgiant branch to the red ...
- 31
0
votes
0
answers
8
views
Stellar structure and evolution book [duplicate]
I am studying stellar structure and evolution. I have read many books about this but I have not finished any of them. Textbook like Dina Prialnik, Paul, Kippenhan, Stellar Interior by Carl J. Hansen ...
1
vote
1
answer
44
views
What is the average prevalence/density of stars in space?
By average density $D$, I mean that, if you look at a huge volume $V$, you would expect to see $V\cdot D$ stars in that volume.
Just a rough answer is fine. I'm sure the prevalence of stars changes ...
- 740
4
votes
2
answers
58
views
At what average rate do supernovas happen?
By average rate $R$, I mean I want an answer with units $$[R]=\frac{\text{supernovas}}{\text{length}^3 \cdot \text{time}}$$. That is to say, if I consider a huge volume $V$ and a long timeframe $T$, I ...
- 740
1
vote
0
answers
9
views
Comparison of temperature between white dwarfs and giants using the Saha equation
“ Consider the comparison of Fe I and Fe II lines in the spectrum of the sun and in the spectrum of a star with a very similar Teff but much lower gravity—for example, the supergiant β Draconis. From ...
- 327
1
vote
0
answers
18
views
How small would iron stars with a mass of 0.50 solar mass be?
I am wondering how small a 0.50 solar mass iron star would be. Would they be the same size as a white dwarf of that mass which would be about the size of the Earth. Or would they be much smaller and ...
- 851
1
vote
1
answer
85
views
How could have Boson Stars formed in the universe at all?
Boson particles have been predicted by some to have been able to form stars known as Boson Stars. I am curious as to how these stars could have formed given that Boson particles are not truly affected ...
- 19
3
votes
1
answer
109
views
Collapse into a black hole in general relativity
I am looking for a paper that would study a mathematical model for the collapse of a star into a black hole (no QM please, just plain old GR). I know about the "dust bowl" model of ...
1
vote
0
answers
61
views
Why are stars portrayed to have pointed corners even when they emit light in every direction
Is it just for representative purpose or does it have any meaning
0
votes
1
answer
25
views
Are there any binary red supergiants?
I wonder if we ever have identified or observed a pair of binary stars (red supergiants).
And I also wonder what would happen if they exploded, (theoretically) as we havent observed it. Also, would ...
- 111
1
vote
1
answer
39
views
What physical properties make fusion of iron unlike lighter nuclei in main sequence stars?
I understand that after fusing lighter nuclei, a main sequence star will either stop fusing or the fusion does not release enough energy to continue the sequence.
What physical properties make iron ...
- 183
3
votes
0
answers
92
views
Degree of time dilation for stars orbiting near Sagittarius A*? [closed]
Sagittarius A* has an estimated mass of 4.154 million solar masses. A number of stars have been found to orbit near Sagittarius A*.
What is the maximum time dilation factor for any of these orbiting ...
- 151
1
vote
1
answer
29
views
Change in absolute magnitude caused by a change in apparent magnitude
Imagine that we have an object with apparent magnitude $m_1$, later, we observe that the same object appears with an apparent magnitude $m_2 = m_1 + \alpha$, then what we can say about the absolute ...
- 11
2
votes
0
answers
56
views
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 ...
- 31
2
votes
1
answer
101
views
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?
- 1,597
2
votes
3
answers
98
views
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 ...
- 1,307
6
votes
4
answers
260
views
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 ...
- 851
1
vote
1
answer
34
views
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 ...
5
votes
1
answer
68
views
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 ...
- 2,835
0
votes
0
answers
29
views
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?
- 1,597
1
vote
1
answer
29
views
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 ...
1
vote
2
answers
120
views
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 ...
- 67
0
votes
0
answers
193
views
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 ...
- 1