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

8
votes
0answers
115 views

gauss-bonnet gravity constraints from string theory

recently there has been advances in observational constraints of gravity theories that contains scalars coupled to the gauss-bonnet topological term: http://arxiv.org/abs/0704.0175 ...
4
votes
1answer
224 views

How much does electromagnetic radiation contribute to dark matter?

EM radiation has a relativistic mass (see for instance, Does a photon exert a gravitational pull?), and therefore exerts a gravitational pull. Intuitively it makes sense to include EM radiation ...
9
votes
4answers
467 views

Explosion in space

I'm curious about what happens if an explosive substance detonates in space. On Earth, I guess a good chunk of the energy released is carried away by shock waves in the atmosphere. But in space, the ...
1
vote
1answer
68 views

Thermal gravitational radiation and its detection

To my poor knowledge on the topic, the gravitational waves that are most likely to be detected by LIGO or other experiments do not have thermal spectrum. But I'm not certain. I know that Hawking's ...
1
vote
2answers
93 views

What allows new born suns to travel away from each other?

What allows massive new born suns to move away from each other, as they have been observed. I would think that their massive gravity would prevent this and cause them to slam into each other.
1
vote
1answer
468 views

What would happen if a hydrogen bomb were to explode in Saturn's atmosphere?

Purely hypothetical since any kind of testing in atmosphere/space is banned by international legislation/agreement. The humans have already bombed Luna so ... what could be expected to happen on ...
10
votes
4answers
6k views

Size of universe after inflation?

Wikipedia states the period of inflation was from $10^{-36}$sec to around $10^{-33}$sec or $10^{-32}$sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. ...
11
votes
2answers
416 views

Can $10^{23}$ stars be treated with methods of statistical mechanics?

Statistical mechanics is used to describe systems with large number of particles ~$10^{23}$. The observable universe contains between $10^{22}$ to $10^{24}$ stars. Can we treat those many stars as a ...
5
votes
2answers
339 views

How convincing is the evidence for dark matter annihilation at 130 GeV in the galactic center from the Fermi Satellite data?

I listened to Christoph Weniger present his results at SLAC today. See his paper is here: http://arxiv.org/abs/1204.2797 and also see a different analysis here: http://arxiv.org/abs/1205.1045. The ...
6
votes
1answer
76 views

Does a celestial system exhibit a collective magnetic field?

Sol exhibits a magnetic field, most of the planets in orbit around Sol exhibit a magnetic field - strong and weak both. Does the solar system as a whole exhibit a magnetic field? Does the paradigm ...
3
votes
0answers
50 views

squeezed radiation astronomy

Squeezed electromagnetic vacuum does have a renormalized energy density smaller than the vacuum. So it makes it in my opinion a inconspicuous candidate for a dark energy carrier. Are there ...
5
votes
0answers
47 views

Experimental tests of Cluster Decmposition

How tight are experimental and astrophysical tests on whether Cluster Decomposition is satisfied at various space-like separations? Is there a review paper or a standard reference on the question? I ...
1
vote
1answer
93 views

Why are galactic centers always brighter than the edges?

As you can see this image http://i.stack.imgur.com/YOt8C.jpg and other galaxy images, the centers generally much brighter. Why is that? Is there a very big star? A very big gravitational field?
4
votes
1answer
192 views

models for astrophysical relativistic jets from compact objects

what is the simplest way to understand the physics of relativistic jets? we know that they have axial symmetry with very tight angular spread, presumably aligned with the axis of rotation of the ...
0
votes
0answers
58 views

How is the universe expanding? [duplicate]

Possible Duplicate: spacetime expansion and universe expansion? Is the space between planets is growing or the space between stars is growing or the space between galaxies is growing?
1
vote
1answer
5k views

Negative and positive energy and Hawking [closed]

I don't have any physics background (except the material we did in high school-long time ago). I was watching a documentary with Stephen Hawking about whether God created the Universe and I could not ...
0
votes
2answers
113 views

Precessional motion of active galactic nuclei

I want to set a simulation for jet which has a precessional motion. The symmetry axis of jet is $z$ axis, i.e. jet is propagating along $z$ direction making angle $\theta$. I set the velocity ...
0
votes
1answer
126 views

Does diffraction contribute to the Black Drop effect?

Two reasons are given to explain the black drop effect here, but I think I came up with a third. Consider a two-dimensional cross section of the situation just after second contact and just before ...
0
votes
1answer
136 views

Radiative transfer equation solution

The solution of the radiative transfer equation for spherical ionized blob : \begin{equation} \frac{dI_{\nu}}{ds} = j_{\nu}-\alpha I_{\nu} \end{equation} and solution is (Ref: ...
1
vote
1answer
1k views

Do materials cool down in the vacuum of space?

Do materials cool down in the vacuum of space? If yes, how does it really work?
3
votes
2answers
205 views

Pressures Necessary for Carbon Detonation

Carbon detonation is a characteristic event of Type 1a Supernova (EDIT: where an accreting white dwarf near the Chandrashankar limit of 1.4 solar masses explodes), an extremely important standard ...
0
votes
1answer
93 views

Is there any way to produce food without sun, synthetically?

Is there any way to produce food without sun, synthetically? I mean if we face solar winter. look at: Is there any way to survive solarwinter like in Sunshine - movie?
2
votes
1answer
533 views

Analogy between magnetic bottle and Van Allen's radiation belt

A magnetic bottle is an arrangement that permits to confine charged particles. Here you can find a review for charged particle rotating in a magnetic field and at the bottom of the page a description ...
1
vote
2answers
114 views

Is there any way to survive solarwinter like in Sunshine - movie?

Is there any way to survive solarwinter like in Sunshine - movie? Solar winter is where for some reason sun looses its capasity to produce radiation( heat etc.). It doesn't loose everything but some ...
0
votes
1answer
79 views

Regarding binary systems

Are binary systems (in case of stars and other celestial bodies) more favorable than independent existence? I've been going through an article regarding pulsars, where it was stated that 'many pulsars ...
4
votes
3answers
222 views

How many stars within 5 parsecs?

I've ran some scripts on some star catalogs, which counted the number of stars with a parallax greater than 200 mas, which should mean everything closer than 5 pc. The results are as follows: ...
1
vote
2answers
48 views

Locating a Comet, how is it done?

How are the comet-hunters able to precisely locate/know about the required comets ? How can they distinguish between comets from such a far distance ? How are they able to estimate the exact time ...
2
votes
2answers
833 views

Parabolic or Hyperbolic?

How can astronomers find the difference between a parabolic and a hyperbolic comet ? What are the criteria that helps them distinguish these ? Can a parabolic comet switch over to become a hyperbolic ...
0
votes
0answers
25 views

Expansion of Universe [duplicate]

Possible Duplicate: Why space expansion affects matter? If the Expansion is prevalent, i.e. it is observable and true then shouldn't that result in the expansion of the Milky Way galaxy, ...
0
votes
1answer
81 views

Gravity and Magnetism on Stars

I am familiar with the fact that Magnetars have a really strong magnetic field and an ordinary star such as the Sun has a very strong gravitational field. But what about the opposite? What is the ...
2
votes
1answer
191 views

When would the proposed black hole at the centre of Milky Way gulp in our solar system? [duplicate]

I've heard and read that our solar system lies near to the peripheral region of the Galaxy. Then accordingly we would have a greater probability of sustaining to eventual gulping down by the ...
2
votes
1answer
481 views

Combined Gravitational Force Vectors in a Spherical Coordinate System

Asking a question here is quite intimidating for me -- while I love Physics, my high-school understanding only allows me to go so far... I've been trying to solve this problem for the last couple of ...
3
votes
1answer
476 views

Why will the increase in the sun's luminosity accelerate with respect to time?

From http://en.wikipedia.org/wiki/Future_of_the_Earth#Solar_evolution At present, nearly half the hydrogen at the core has been consumed, with the remainder of the atoms consisting primarily of ...
0
votes
1answer
123 views

Is it possible to mould _ruptures_ in Space-time?

In one of the documentaries hosted by Morgan Freeman, a reference was made that just like an ordinary three-dimensional object like a ruler has scratches and cracks, in the same way there might be ...
2
votes
1answer
219 views

How early can scientists detect that a deadly asteroid will hit planet earth?

With the advancements in science and technology, how early can scientists of the world detect that a certain asteroid will hit planet earth and cause damage? Are there any impact avoidance strategies ...
1
vote
1answer
359 views

How does a star wobble due to orbiting bodies

What equations determine how a star wobbles in response to an orbiting planet, and can it be used to determine the mass of distant objects based on the wobble? If there are other more reliable ...
2
votes
1answer
109 views

Black Holes, New Branes and Stars

Could a dying star in one brane ( assuming that we live in a world of multiple branes { not a Randal-Sumdrum model of a single brane}) be the start of the birth of the star ( more precisely Super ...
0
votes
1answer
144 views

Proportion of energy compared to mass in universe

In Wikipedia (http://en.wikipedia.org/wiki/Dark_matter), there is a picture that shows us the proportion of matter and energy in the current universe - CMB. It seems to suggest there is nothing that ...
2
votes
1answer
163 views

Earth's magnetic field, could the poles be reversing?

Lately, I've been 'monitoring', if you will, the earths magnetic field, i've come across some strange looking activity periodically. I exchanged some emails with a guy from NASA today, Joseph Gurman, ...
0
votes
2answers
400 views

Calculating eccentricity from semi-major axis, position and velocity of particles

I'm trying to calculate the eccentricity of a binary system's body knowing the bodies' velocities, positions, masses and the semi-major axis. I am only trying to calculate the eccentricity for one of ...
3
votes
1answer
94 views

missing dark matter?

A recent arXiv article measures the variation of gravitational potential in a local region around the solar system, and from that it tries to infer the mass density. Are there any valid ...
6
votes
2answers
1k views

Do the stars imaged by a telescope even exist at present?

I know that we now have telescopes which can capture the images of the stars and galaxies millions of light-years away from us. Does the telescope capture the past image of the star, i.e. the light ...
6
votes
1answer
269 views

Why do the stars in the galaxy core move so fast?

There are a bunch of stars orbiting the black hole in the center of our galaxy. These stars move at huge speed. Why do we see this? Why do the black hole not impose any noticeable time dilation on ...
3
votes
1answer
126 views

What are some ways that humans could have influence over what sequence a star was in?

How would a society go about either preventing our sun in its primary sequence from going into a Red Giant a billion years from now? Or perhaps, accelerating the process of going from main sequence ...
-2
votes
1answer
174 views

What is solar storm?

I have tried to search through the internet about the definition of solar storm or what this term mean but i could found what it means. Also, what is the difference between the geomagnetic storm
6
votes
1answer
120 views

What prevents stars in globular clusters from merging over time to form a black hole?

Globular clusters are apparently very very old, and the density of these clusters appears to increase as one approaches the center of a cluster. Orbits are bound to be chaotic, since there is no ...
4
votes
1answer
165 views

Simulating a black hole binary system

As part of a project for my degree I am writing code to simulate N-body gravitational interactions, however I have to then use this code to investigate something. Struggling to think of ideas I ...
3
votes
3answers
371 views

Shouldn't stars disappear from our view due to expansion?

The currently accepted theory of the expansion of the universe would suggest that for any point in the universe, there is a 'boundary' (somewhat like the Schwarzschild radius) beyond which it cannot ...
5
votes
4answers
779 views

Why doesn't the Earth leave you as soon as you escape it?

I've always wondered, that since the Earth is moving at a very fast velocity around the Sun, why is it that when astronauts leave the Earth, the Earth doesn't immediately move away from them at ...
8
votes
3answers
535 views

Do neutron stars reflect light?

The setup is very simple: you have a regular ($1.35$ to $2$ solar masses) evolved neutron star, and you shine plane electromagnetic waves on it with given $\lambda$. Very roughly, what shall be the ...