2,469 reputation
216
bio website
location
age
visits member for 1 year, 3 months
seen Mar 14 at 18:22

programming numerical algorithms for astrophysical applications.


Feb
27
comment Fourier Transform of Galaxy Images
The Fourier transform per se will not help you to find overlapping object. Where does this idea come from?
Feb
6
comment Why there are other planets in our solar system?
Are you asking for the reason (that there are planets) or for their purpose?
Feb
6
comment Why there are other planets in our solar system?
Why are there other people on this planet. Only I am important. What is the significance of others, such as user804401? I receive food from the plants and animals. In a similar way do I receive any food from other people?
Feb
6
comment Does one need to take into account finite gravity speed in N-body simulations?
Most large-scale N-body simulations (e.g., stellar clusters, galaxies, galaxy clusters, ...) use general relativity Wrong For up to galaxy scales, one safely uses Newtonian gravity. For larger scales (so-called cosmological $N$-body simulations), one uses GR only to describe the (assumed) smooth background (universal expansion), but Newtonian physics otherwise.
Feb
6
comment Galaxy rotation curve and dark matter
The authors of that book should have mentioned the caveat, that it only introduces a small error, and that in the scientific literature (of which that book is no part) such simplifications are not made (unless the errors introduced are far smaller than other sources of error). If they did not, then this is just another example of poor practice in presenting science to the public.
Feb
5
comment Galaxy rotation curve and dark matter
Can you substantiate your claim (that galaxy rotation curves are calculated from what you call the shell theorem)? For near-spherical object, the error one makes with this assumption is very small (at most a few %).
Jan
26
comment How do stars or galaxies get their spin?
@HugoRune I edited the question somewhat, but yes, it is somewhat similar to the Brownian motion, except that the expectation value is much larger. Don't forget that the ISM is not smooth, but has structure on many scales (while a gas has only the molecular structure and is smooth on larger scales up to macroscopic scales, when there may be structure again).
Dec
12
comment What is the most oblate astronomical object known?
The question is still ill-posed. Strictly speaking, there are no oblate spheroids. Oblate spheroid is a concept and real objects can only ever approximate such a concept. The question then is how well does the object have to satisfy this concept? There may be a pretty flat asteroid which happens to be near oblate (but not flattened by rotation, of course -- that was not required in the question).
Dec
11
comment What is the most oblate astronomical object known?
I think your question is ill-posed, as it uses the concepts of polar and equatorial diameter. However, for an irregular object these are not well-defined.
Dec
11
comment What is the most oblate astronomical object known?
Well, that's not what you've asked (originally). Perhaps you should qualify your answer then. IHMO, my suggestions are not trick answers, but honest and correct answers to your original question.
Dec
9
comment What is the most oblate astronomical object known?
What's an object? Would Saturn's rings qualify? -- they are pretty flat. Otherwise, what about the Galactic disc? or other astrophysical discs (accretion discs have aspect ratios 1:1000)? None of these are fully self-gravitating: there is always a round component contributing or even dominating gravity...
Dec
3
comment Why does the distance between Sun and Earth stay the same?
@StanLiou Do you have a www reference for that?
Dec
3
comment Why does the distance between Sun and Earth stay the same?
Being pushed some way doesn't imply that you're necessarily falling that way. See also the update to my answer.
Dec
2
comment Why does the distance between Sun and Earth stay the same?
did you mean to ask why the Earth-Sun distance remains unchanged?
Dec
1
comment Likelihood of a stable system with a dwarf planet's orbit inside that of a gas giant
The orbit of a dwarf planet in the inner planetary system is almost certainly chaotic and hence unstable, unless it is in orbital resonance with a major planet.
Nov
29
comment Why does the face of the moon 'sync' with the earth?
This is not a force, but radiation. Radiation also decays like $r^{-2}$, like gravitational forces (both is simple geometry).
Nov
28
comment How is the maximum density in a circumstellar disk determined?
If $r$ is the spherical radius (which is the usual convention for this symbol), then this is not a disc at all... If it is cylindrical radius, it is not a disc either, but a cylinder, since there is no $z$ dependence.
Nov
28
comment Why does the face of the moon 'sync' with the earth?
realitively weak forces such as gravitation lol. If you meant "gravity", that's the weakest force on small scales, but the only force on large scales. So it doesn't matter that it's "weak".
Nov
28
comment What is a low mass Black Hole?
That paper made the term "low-mass black holes" up. Moreover, it starts from a wrong premise, namely that the formation of supermassive BHs after $10^8$ years is a problem and hence requires some drastic solutions. All ideas that BHs can simply form from the direct collapse of gas are wrong, as they violate the Eddington limit by many orders of magnitude.
Nov
18
comment Is there enough hydrogen left after a star dies so another star will have enough to light up?
oops. yes, thanks.