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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52
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2answers
6k views

Why is the Sun almost perfectly spherical?

Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest ...
-1
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1answer
83 views

How do you project a Sersic profile into 3D?

I'm attempting to create a velocity profile for the M31. I have a Sersic profile from a paper by Sofue et al (2009), but I'm unable to project it into 3D space in order to get the actual 3D density ...
6
votes
2answers
101 views

Do the magnetic moments of neutrons mutually align to produce the magnetic field and emission beams of a pulsar and/or magnetar?

In this graphic of a pulsar the emission beams are at the north and south poles of the neutron star's magnetic field. I've read that the Earth's magnetic field is produced by a dynamo effect, whereby ...
-1
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1answer
44 views

What do you see if you directly observe your destination while in warp? [closed]

Say you are traveling in a warp bubble towards Earth from 10,000 lightyears away with an ETA of 24 hours. On the front of your ship, you mount a high powered telescope pointed directly at Earth (your ...
-1
votes
1answer
62 views

In what ways does the sun output energy?

I'm curious about the energy output of the sun, and how it breaks down. What fraction is from EM radiation, solar wind, neutrinos, et cetera? How does energy output vary over the EM spectrum? I was ...
2
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1answer
111 views

How to calculate the radius of a main sequence star based on mass?

What would I need in addition to the mass to figure out the radius of a main sequence star?
1
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1answer
64 views

How does fusion work in the Sun if neutrons have more mass than protons?

According to my textbook, the next result of the fusion reactions in the Sun is: 4H -> He + neutrinos + gamma photons However, if hydrogen atoms are basically a proton and helium atoms are 2 protons ...
0
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0answers
35 views

What is the physical meaning of source function in radiative transfer?

I know that it's the ratio between emission and absorption coefficients.But what does it actually mean? Can you please explain?
51
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4answers
5k views

Do solar systems typically spin in the same direction as their galaxy?

Is the net angular momentum vector of our solar system pointing in roughly the same direction as the Milky Way galaxy's net angular momentum vector? If yes or no, is that common for most stars in the ...
0
votes
1answer
67 views

Can anyone think of any astronomical phenomenon that could be due to engineering projects of an advanced civilzation? [closed]

It has always seemed to me that there could very well be evidence of advanced civilizations in other parts of the galaxy/universe that are staring us in the face. Within a thousand years, heck, maybe ...
6
votes
4answers
223 views

Speed distribution of objects in the universe

If we pick a reference frame where, for example, our planet is standing still (although it should be irrelevant), what would the speed distribution of all objects in the universe look like? For the ...
1
vote
0answers
41 views

What is the definition of the “stellar angular diameter” in stellar astronomy?

(Following the definitions here: http://arxiv.org/pdf/astro-ph/0509535.pdf ) What is the "stellar angular diameter", as measured by astronomers specializing in stellar astrophysics? Using the ...
0
votes
1answer
86 views

Does spaghettification really happen with conditions found close to a black hole?

This website tries to explain why the term spaghettification doesn't actually occur when something gets close to a black hole. The argument of the author is that the equations we use to predict the ...
1
vote
0answers
29 views

Misbehaving singular isothermal sphere potential

The singular isothermal sphere (SIS) is a useful simple model often used in astrophysics. It has density profile: $$\rho(r) = \frac{\rho_0 r_0^2}{r^2}$$ This is well known to have some quirks ...
0
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0answers
22 views

Do the arms of spiral galaxies differ based on the speed of which the galaxy is rotating?

If I were to take a circle with strings attached to it and spin it, the strings would behave differently based on how fast the circle is rotating. Do galaxies behave the same way?
1
vote
1answer
59 views

The Thomson scattering optical depth for a photon ar radius r

I am looking to understand some more about the physics of gamma ray bursts. In particular I am looking at the origin of the "prompt emission". Some of the energy associated with this prompt emission ...
1
vote
0answers
46 views

Origin of Jet production: Active Galactic Nuclei

According to Netzer's book on Active Galactic Nuclei (AGN), pair production ($\gamma \gamma \leftrightarrow e^+ e^-$) which causes AGN jets presumably happens in "the corona of the central accretion ...
0
votes
2answers
98 views

Density of the Sun

Being either on the surface or somewhere inside; where is the density of the gases of the Sun equal to the density of the ground we stand on here on earth?
1
vote
2answers
95 views

What causes the death of the Sun?

In a previous question I learned that in each second only a miniscule portion of the total hydrogen in the Sun is converted to helium and that the number is 1/10^18 of its mass converted each second. ...
10
votes
2answers
284 views

Would a rocky planet orbiting so close to a very hot star eventually vaporize?

I was thinking about the physics behind a hypothetical scenario where a planet the size and the mass of the Earth is orbiting so close to a very hot star and what the long-term fate of such a planet ...
0
votes
1answer
121 views

Where is the Hydrogen the Sun consumes?

I understand the Sun consumes 600,000,000 tons of Hydrogen each second. Where is this Hydrogen? Is all the Hydrogen the Sun will ever consume inside it or are there vast amounts of Hydrogen in space ...
0
votes
1answer
58 views

Will climate change cause the Moon to move away from the Earth at a faster rate?

The Moon is moving away from the Earth at a rate of 38.08 ± 0.04 mm/year. This is caused by the tidal bulges being pushed ahead of the Moon as the Earth rotates and the landmasses interact with the ...
2
votes
3answers
151 views

Are there more photons than nuclei within the Sun?

Are there more photons than nuclei within the Sun? Is there a good way to estimate what the ratio would be?
1
vote
1answer
38 views

Origin of Stellar Nurseries

What is the mechanism thought to cause huge stellar nurseries to form e.g. eagle nebula?
2
votes
2answers
53 views

Are there hypothetical processes which allow the existence of a fission powered star?

I know this is impractical given the rarity of heavy fissile elements in the universe (contrary to the abundance of fusion friendly elements like hydrogen), but is there any process via which a ...
2
votes
3answers
116 views

Can there be eternal stars?

the question is quite straightforward: Can there be stars that shine forever without ever collapsing nor growing? Do we know some really, really old stars? (whatever age that might be) I hope to ...
6
votes
0answers
117 views

Relativistic rotational squeezing?

I would like to consider a sphere rotating at very high angular speeds, such that the speed in its equator would be relativistic. This is very similar to Ehrenfest paradox situation, except that ...
1
vote
0answers
41 views

Signal-to-Noise ratio given pixel intensity map [closed]

I have a question regarding calculing the SNR of a signal given the pixel intensities. Say I'm given the pixel intensity values below: $\begin{array}{ |c|c|c| } \hline 3&3&3&3&3 \\ ...
1
vote
1answer
25 views

Looking for current review article on the Oort Cloud

I'm sure someone will tell me just to Google, but I'm struggling to find a truly detailed and informative article explicating our current understanding of the Oort Cloud. Could someone please ...
0
votes
1answer
57 views

How do inert helium cores in sub giant stars create a pressure force?

I'm reading about the sub giant branch (SGB) and the evolution to the red giant branch (RGB). On the SGB stars have burned all hydrogen into helium, as a result, they have an inert helium core. The ...
1
vote
1answer
45 views

Can the lithium test be applied to differentiate brown dwarfs from other substellar objects?

The lithium test is often used to differentiate brown dwarfs from low-mass M-type dwarfs (see e.g. Martin et al. (1994)), because brown dwarfs (at least the lower-mass ones) do not burn lithium, ...
2
votes
4answers
75 views

Navigating to a distant star

Suppose I have a space ship that can travel at $0.9c$, and I'm going to a star located at 20 light years or so from the Sun. From a practical point of view, if I keep pointing the nose of my space ...
9
votes
1answer
548 views

Do supernovae produce an appreciable amount of lithium?

David Z's answer to this question got me wondering - is any appreciable amount of lithium produced as the result of a supernova explosion, either by fusion (which seems unlikely to me, but I don't ...
0
votes
2answers
46 views

In stellar astrophysics, what is the difference between protostellar disk and circumstellar disk?

I have noticed both the terms "protostellar disk" and "circumstellar disk" in the stellar astrophysics and exoplanet literature. What exactly is the difference?
0
votes
1answer
25 views

Help reading power spectrum graphs?

How would I go about figuring out how long a source was measured when given a graph of the power spectrum? From notes I'm following, they just state the total observation time as being roughly ...
1
vote
0answers
33 views

Lorentz factor correction for luminosity

I am looking at the physics behind gamma ray bursts, working through a comprehensive review Kumar & Zhang (2014) (arXiv link). On page 92, Eq (111) the luminosity or a relativistically expanding ...
1
vote
2answers
45 views

How can contact binaries persist?

This answer discusses contact binaries, which I did not even know existed. I can understand how they could exist for a short time (maybe) as gravitational waves carry off energy that causes the stars' ...
3
votes
0answers
44 views

Why do TiO bands dominate M dwarfs?

I'm new at understanding stellar classification and the spectral classification of stars. What is the exact reason TiO molecules (titanium oxide) dominate the spectrum for M dwarfs? How did this TiO ...
2
votes
1answer
148 views

What is the largest possible mass for a stable planet made of iron?

Consider a large spherical planet made of pure iron. Think of something similar to Mercury or Earth without its mantle, only much bigger, though those planets have elements other than iron mixed in ...
1
vote
1answer
42 views

Short Gamma Ray Bursts from black hole mergers

I have read in passing that short gamma ray bursts can be caused by the merger of 2 black holes in a binary system. I have Googled but can't seem to find any good sources describing the phenomenon ...
0
votes
1answer
63 views

Quantum gravity- Vacuum catastrophe

Why does the predicted mass of the quantum vacuum have a very little effect on the expansion of the universe?
3
votes
2answers
75 views

Do gamma ray bursts play a role in cosmic evolution?

If gamma ray bursts were to interact with gas clouds in the early universe, might it be a relevant factor in star production?
0
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1answer
44 views

Is it possible that a satellite once was a small planet?

Very common fact that a planet has satellite which revolves around it and has an impact on that planet too.Is it possible that a small planet had been bombarded with a big planet and transformed ...
0
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0answers
9 views

Region of resonance and overlap

In planetary dynamics what does a region of resonance (mean motion) between two bodies mean and how to quantify the region? How does resonance overlap occur and what are its consequences? What is ...
4
votes
1answer
76 views

Shoemaker-Levy 9 impact on Jupiter

When the comet Shoemaker-Levy 9 impacted with Jupiter it created a ball of fire 3000 Km high and it left a mark on the surface of the planet that was visible for weeks (source: Wikipedia). How was the ...
1
vote
1answer
47 views

How was hydrogen gas (H) obtained by spectroscopists? Why is there more H than H2 in space?

Introductory quantum mechanics lessons talk about emission and absorption spectra for the hydrogen gas, and then give you an explanation as if this gas were pure $H$ atoms, and not the $H_2$ molecule ...
3
votes
2answers
76 views

How can we determine the internal structure of a star from distance?

See here for the discussion leading to this question. In essence, I was wondering whether there were methods to differentiate between a star destined to become neutron star and a star destined to ...
1
vote
2answers
112 views

How much of an asteroid mass can be in platinum or rare metals?

There are many articles about the 2011 UW-158 asteroid which will pass earth tonight. The interesting thing about this asteroid is that it is said to contain $5.4 trillion worth of platinum. Many ...
2
votes
0answers
59 views

Geometry of magnetic field lines in plasmas/MHD

So I'm trying to gain an intuitive grasp of plasmas and magnetohydrodynamics. There's a couple of questions I have. What does it means magnetic field lines are frozen into "plasmas"? Is it that ...
3
votes
1answer
79 views

What is the process that causes a collapsing star to bounce back? [duplicate]

Can someone explain the process by where a star collapses and bounces back. I haven't been able to find a good explanation of the bounce. Edit here, I was wondering specifically where the energy of ...