The application of physical theory to celestial systems such as stars, planets, galaxies, supernovae, and black holes. Astrophysics proper is concerned with explaining phenomena more so than making observations, the latter falling under the purview of astronomy.

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Why are stars white?

That is may be a easy question, but I am not a professional. The sun is a star and when I look at the sun is usually yellow. Why stars in the night are white? I suppose is for the distance. What is ...
2
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1answer
64 views

Angular momentum in planetary disk formation

This question is actually more linked to astronomy and astrophysics than to pure physics. I tried posting it on the astronomy page, however it got no answers, so I though this page might help. ...
3
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1answer
37 views

Tidal tails of galaxies after collision

When there is a collision of 2 disc shaped galaxies, there is a tail formation created from both the galaxies. I read here that this was due to tidal forces, but I couldn't figure out how this ...
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1answer
81 views

Mass-to-light ratio and rotation curve from brightness profile

This should probably be basic but I've been looking for days and I can't find how to (I'm probably over complicating, but still). I want to calculate a rotation curve for some spiral galaxies. From ...
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2answers
74 views

Name for Earth?

What is the proper word for 'Earth', as in 'Solar' and 'Lunar'? I cannot find this anywhere; I am guessing there is a word that starts with geo?
6
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0answers
57 views

Metal-rich star formation

While discussing star formation on cosmological scales with some classmates, we mentioned the breakdown between the different stellar populations via metallicity: Population III: $Z = [{\rm Fe/H}] ...
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44 views

The standard textbook on supernovae?

This is a straightforward question: What is considered to be the standard treatment of supernovae? Could be a textbook, lecture notes, review article, etc.
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3answers
172 views

Why does fusion stop at iron when nickel is most tightly bound?

My understanding is that stellar fusion naturally stops at iron because it is energetically unfavourable to grow the nucleus further. But iron is only the third most tightly-bound nucleus, nickel is ...
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0answers
17 views

For a Plummer model mass distribution, what is the timescale of dissolution?

Given an initial system of masses distributed in a Plummer model close encounters cause stars to gain enough energy to leave the system. What is the timescale over which the whole cluster with N ...
6
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2answers
557 views

How is a blackbody spectrum formed in the Sun?

Sunlight can be treated as BB radiation. Why is it a continuous spectrum while the sun contains only a few elements and the radiation from the jumps between atomic levels are discrete? How does the ...
5
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1answer
191 views

What types of fusion reactions happened in population III stars?

I have read that, in smaller stars, such as our Sun, the fusion reaction that takes place is a proton-proton chain, or PP chain for short. From what I have learned, in larger stars, a different ...
3
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1answer
51 views

What was the significance of the ionization caused by the Population III stars?

I am reading that the ultraviolet light that radiated from the first stars would ionize the surrounding gas and apparently, all of the matter in the universe would eventually become ionized. So, ...
2
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4answers
356 views

What happens during gravitational collapse to cause the formation of a star?

I know that stars are formed from dense regions in large gas clouds. I know that when gravity causes the mass of the clump to get so big that its internal pressure can't sustain it, it collapses and ...
5
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1answer
83 views

Experimental Data for Mass Distribution of a Galaxy

My goal here is not to discuss dark matter in general. I know there are many other observational clues that hint us towards Dark matter. My goal is simply to understand this argument here a little ...
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2answers
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Is there a limit as to how fast a black hole can grow?

Astronomers find ancient black hole 12 billion times the size of the Sun. According to the article above, we observe this supermassive black hole as it was 900 million years after the formation of ...
0
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1answer
25 views

Woltjer's Theorem, partial or total derivative?

Morning everyone.. I am currently studying Plasma Physics on a recent book named "Basics of Plasma Astrophysics" by Claudio Chiuderi and Marco Velli. While demonstrating Woltjer's Theorem they state ...
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1answer
61 views

Does all the theoretical work of astrophysicists have to be confirmed by the observations of astronomers?

I am a chemist an I have some doubts about the work of astrophysicists. I know that astrophysicists do a lot of theoretical calculations based in other theoretical work and also based in real ...
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0answers
28 views

What's the cause of this gap in this simulation of the Nice model?

A previous question brought me to this video (which has a spectacular change at about 0:34). It shows the orbits of Jupiter, Saturn, Uranus, Neptune, and what appear to be trans-Neptunian objects. ...
3
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1answer
38 views

Solar System Snow Line: 5AU or 2.7AU?

I am trying to update the Wikipedia article "Frost Line (astrophysics)". During my last update (by QuantumShadow), I noticed that different sources cite different values for Solar System water ice ...
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0answers
29 views

Density of an astrophysical ring of fluid around a star

*An equilibrium ring of isothermal fluid orbits a star at radius R. In the plane of the ring, mechanical equilibrium results from a balance of centrifugal force and the gravitational force of the ...
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2answers
1k views

How can a gas giant be about the same size but six times more massive than Jupiter?

I've just read this article: http://www.sci-news.com/astronomy/science-kepler-432b-new-super-jupiter-exoplanet-02490.html And I wondered how this could be possible? Maybe it's because this gas giant ...
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0answers
37 views

For gravitational wave from twin stars, how was the tidal effect counted?

As the primary indirect evidence, the work on calculating the rotational slow down earned the 1993 Nobel prize. However, I cannot find any where mention how the work deal with the tidal effect. Are ...
0
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0answers
26 views

How much cheaper and smaller on average is SiPM technology over conventional PMTs?

I've heard it said that some of the major advantages of silicon photomultipliers are its low cost and compactness when compared to widely used photomultiplier tubes, but haven't found much information ...
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3answers
265 views

Is there an exact formal definition of the Universe?

I've read several articles about observable Universe, Universe and Hubble volume, including Wikipedia article and references on it, and I wondered: Is there a formal, rigorous definition in physics of ...
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23 views

Modeling atmospheric reentry with respect to the rotation of a planet and its atmosphere in a simulation

I am creating a hard science fiction flight simulator. I am a civil engineering student, so its a little out of my area of study. Currently I model air resistance on the velocity difference between ...
1
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1answer
477 views

Kinetic energy of an expanding sphere [duplicate]

In the study of Newtonian stellar structure, Weinberg (1972) writes The uniform dilation of a sphere with uniform density will give it a kinetic energy $$U=\frac{3}{10}M\dot R^2$$ I don't ...
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25 views

How to estimate the chance of cosmic radiation reaching Earth?

Say some cosmic radiation like X-ray generated by some distant star is towards Earth, what is the chance that it reaches Earth successfully without being blocked or deviated or absorbed?
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1answer
45 views

What does multi-periodicity mean in stellar pulsations?

How can there exist multi-periodicity in stellar pulsations? http://www.kitp.ucsb.edu/sites/default/files/kitp/preprints/moskalik2.pdf How can one visualize a multi-periodic pulsation or oscillation?
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1answer
43 views

Are the gravitational redshift and blueshift factors inverses of each other? [closed]

at a point in gravitational field assuming swcharzschild metric and the exact analysis. The other point in context is infinity. It would be helpful if you can provide citation/source of the ...
0
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1answer
73 views

What is the total matter equivalent of the Sun's output per year?

Say we can collect all the energy from the sun's output and all the particles from the solar wind. If we had an energy to mass converter and turned everything into say, carbon, how many kilograms of ...
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1answer
43 views

What makes red giants big? [duplicate]

I read some about red giants and so far I understand red giants become exhausted of burning hydrogen in the core, so then start hydrogen burning at shell and may or may not be burning helium in the ...
1
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1answer
59 views

Confusion with the meaning of CMB

We say that CMB is the radiation leftover from big bang. When we measure the radiations i.e., the flux of photons in a given microwave range (say 0.1cm to 70cm, for example), in deep sky, there are ...
8
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1answer
184 views

The Solar System explosion in the Nice model

This video depicts one variant of the Nice model (pronounced "neese", like the city in France). I'll briefly describe it in case the link ever dies. Here is the initial configuration: The four ...
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1answer
134 views

What is an 'S-factor' in nuclear physics?

I have seen the "S-factor" in many places, but I've never read an explanation of what it actually is. I have read that it is related to the cross-section of a reaction, but that's about it.
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29 views

What is a threshold/subthreshold state and resonance?

I understand what a 'state' is for a quantum mechanical system, but upon reading a paper on reducing the error for a particular nuclear reaction rate I saw the following sentence. "The extrapolation ...
0
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1answer
44 views

Are the large moons of Jupiter, Saturn, and Neptune still cooling and does this give and indication of their age?

The core temperatures and the rate at which they emanate heat should correspond to their estimated age. Other forces may create some heat such as the tidal locking that is supposed to be the source of ...
24
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2answers
3k views

Why would a black hole explode?

It is common in popular science culture to assume that Hawking radiation causes black holes to vaporize. And, in the end, the black hole would explode. I also remember it being mentioned in A Brief ...
2
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1answer
44 views

r-process: Is it correct to talk about “primary” and “secondary” r-processes?

This website, written in 1994, makes a differentiation between the "primary" and "secondary" r-processes in the context of astrophysics. As far as I can tell the main difference between the primary ...
2
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1answer
72 views

Difference between collisional and collisionless Boltzmann equations?

Reading an excellent answer, I've read about there are different Boltzmann statistics for a collision-less system (f.e. stars in a galaxy) and in a system with collisions (f.e. gas in a closed box). ...
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2answers
91 views

Why has the amount of star formation in the Universe decreased over time?

If you like, refer to my old question from the last year, about star formation rates and their declining, answered by Rob Jeffries. I'm now examining why this process happens. It appears that in ...
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0answers
46 views

Would a supermassive black hole accretion disk really vaporize solid objects?

Both the movie Interstellar and Greg Egan's Incandescence involve worlds deep inside accretion disks of large holes, kept at a comfortable temperature. Is this (remotely) realistic? Although ...
1
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1answer
169 views

Galactic Rotation Speeds - Ehrenfest Paradox, Gravitational time dilation, Dark Matter - all of the above?

The observed paths and speeds of objects, part of some distant galaxy, do not match up with speed vs distance curves it seems - the observed speeds are not falling off in fact they're trending as ...
4
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1answer
120 views

What would happen to the universe if dark energy started “disappearing”?

Terribly naive question, I know. Obviously, not simply "disappearing", but if it could, theoretically, be absorbed or "used" somehow, what would happen to the universe? Would it stop expanding, would ...
6
votes
1answer
108 views

Do the stars in a galaxy have a thermal kinetic energy distribution?

I think, there is practically everything given to that: many point-like masses, able to exchange energy pseudo-randomly, and far long enough time to reach a thermodynamical equilibrium. Of course, ...
0
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0answers
55 views

How is optical depth (opacity) related with gas pressure?

In stellar atmospheres, if we are given the gas pressure on the surface level of a star $P_{0}$ and we are expected to calculate the gas pressure on a deeper level (say 10000km) of the star, what kind ...
2
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1answer
74 views

Can a star with a constant density profile be possible?

The equation of states for a star is given by a polytropic equation, where density depends on the $n$th power of $\theta$. Please refer to the literature First, what is this $\theta$? It can't be a ...
2
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1answer
83 views

What would a very massive rocky body look like?

I have a basic understanding of how gaseous bodies behave according to their mass: "Low mass" bodies are gas giants (or brown dwarfs), Beyond a certain mass, hydrogen fusion starts, making a star, ...
2
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2answers
91 views

Position of Neutron Stars in H R diagrams

Why is that neutron stars are never depicted in a Hertzsprung-Russell diagram? They can be placed in the bottom left corner but you will never find any diagram in literature showing neutron stars.
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40 views

Boltzmann equation (Number density)

I'm trying to understand the Boltzmann equations use in the early Universe. The derivation is somewhat tedious, but in the end I end up with: $$a^{-3}\frac{d}{dt}\left(n_1a^3\right) = ...
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0answers
35 views

Gravitational collapse (artificial). Is it possible? [duplicate]

I am rather a beginner to this field, so please forgive me if this is a very meaningless question. If I were to somehow increase Jupiter's mass by adding more hydrogen to its atmosphere, can I ever ...