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.

learn more… | top users | synonyms

1
vote
0answers
33 views

Which technique is used to measure huge astronomical distances which are in terms of billions of light years? [duplicate]

I know what a "light year" means. However, I am very curious to know about the technique through which scientists are able to calculate the distance of various astronomical bodies from earth which are ...
6
votes
2answers
1k views

What would it be like “inside” a star?

This question was triggered by a discussion regarding the computer game Elite: Dangerous, where spaceships routinely operate in close proximity to stars (two or three light seconds away), at which ...
4
votes
1answer
28 views

PP Chain and CNO cycle relationship

At what temperature would the energy generation rates of the PP-Chain and CNO cycles be roughly equivalent? The dependences are so vastly different that I am wondering how and by what equations they ...
4
votes
1answer
36 views

How much mass is typically ejected from a supernova?

How much mass is released from a supernova of a 15 solar-mass star? 20? 25? What is the relation between star mass and mass ejected?
-4
votes
0answers
38 views

How would I find equatorial velocity given an R of 10 KM and a P of 0.0002 sec? [closed]

Any help would be appreciated. I can't find anything relating to this problem online.
3
votes
1answer
53 views

How much atmospheric pressure (CO2) is required to carry iron oxide dust in the wind?

It is common knowledge that there are dust devils and dust storms on Mars. But can we demonstrate that the atmospheric pressure on Mars, which is 0.6% of the pressure we experience on Earth, provides ...
27
votes
3answers
3k views

Can the Sun capture dark matter gravitationally?

I think my title sums it up. Given that we think the dark matter is pseudo-spherically distributed and orbits in the Galactic potential with everything else, then I assume that its speed with respect ...
0
votes
0answers
30 views

What does it mean for a state to have a negative partial decay width?

I don't understand what it means when a particular decay mode has a negative partial decay width. I'm guessing the total decay width for a particular system must always be positive (now that wouldn't ...
27
votes
4answers
4k views

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
votes
1answer
42 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. ...
1
vote
0answers
21 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 ...
0
votes
0answers
72 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 ...
0
votes
2answers
63 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?
3
votes
0answers
42 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}] ...
1
vote
0answers
40 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.
4
votes
2answers
94 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 ...
1
vote
0answers
14 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
votes
2answers
523 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 ...
6
votes
1answer
147 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
votes
1answer
45 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
votes
4answers
255 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
votes
1answer
70 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 ...
26
votes
2answers
2k views

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
votes
1answer
22 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 ...
1
vote
1answer
54 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 ...
0
votes
0answers
22 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. ...
0
votes
0answers
18 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 ...
0
votes
0answers
27 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 ...
10
votes
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 ...
1
vote
0answers
36 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 ...
1
vote
0answers
22 views

Cosmological and astrophysical bounds on physics beyond SM [closed]

There are many cases when cosmological and astrophysical observations make restrictions on particle physics models. For example, some axion models are rejected by white dwarf luminocity functions, ...
0
votes
0answers
24 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 ...
4
votes
3answers
239 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 ...
1
vote
0answers
22 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
vote
1answer
446 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 ...
0
votes
0answers
24 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?
0
votes
1answer
38 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?
-1
votes
1answer
42 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
votes
1answer
67 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 ...
1
vote
1answer
40 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
vote
1answer
56 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
votes
0answers
141 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 ...
1
vote
1answer
105 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.
0
votes
0answers
26 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
votes
1answer
35 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
votes
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
votes
1answer
39 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
votes
1answer
64 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). ...
1
vote
2answers
87 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 ...
1
vote
1answer
121 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 ...