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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1answer
149 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
5
votes
1answer
60 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 ...
3
votes
1answer
133 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 ...
2
votes
2answers
229 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
361 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 ...
5
votes
3answers
280 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 ...
10
votes
1answer
511 views
What will happen if a gamma-ray burst hits the Earth?
Is there any probability that a gamma-ray burst (GRB) could affect the Earth?
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1answer
348 views
Shouldn't the fourth dimension be energy/mass, and not time? [closed]
First of all, I am in 8th grade. That doesn't mean you have to make your answer simple and easy to understand, but I ask you not to be too critical of my query/theory, because I don't consider myself ...
5
votes
2answers
107 views
Io - Turned inside out
In a lot of the descriptions of the moon Io it frequently states that the moon, because of volcanic activity, has been literally "Turned inside out". What exactly is meant by "Turned inside out" and ...
4
votes
1answer
218 views
Accuracy and assumptions in deriving the Tully-Fisher relation
I understand the mathematical derivation of the Tully Fisher relation from basic physics formulas, as shown on this site. However, after using the physics equations, it seems that several assumptions ...
2
votes
1answer
147 views
Function to determine Earth-Moon distance vs. time
I had no luck trying to find a function that determines the distance between Earth and Moon versus time.
(Moon ground level to Earth sea level)
Accuracy:
the acceptable time range would be for ...
4
votes
2answers
67 views
How is it that some nebulae are rotating and others are not?
First, I should make it clear that this isn't a question about angular momentum (unless I may have completely missed something). It is my understanding that a nebula must have some inherent initial ...
6
votes
1answer
134 views
Frequency of nomad planets passing within 30 AU of the sun
A recent estimate by the Kavli Institute for
Particle Astrophysics and Cosmology (a joint
institute of Stanford and SLAC) is that there
are circa 100000 times as many 'nomad planets' as stars
I ...
2
votes
1answer
55 views
From Computational Astrophysics to Finance [closed]
If for some reason, an Astrophysics graduate decides to shift to Finance will he/she be in a better position (given his/her overspecialization) to make a transition compared to his/her counterparts ...
1
vote
0answers
67 views
Cosmic radiation cutoff at LOW energies?
The energy spectrum of the cosmic radiation (not CMB) is limited to both sides.
I know about the GZK-cutoff at high energies. Basically the interaction probability for photons of energies above 10^20 ...
4
votes
0answers
34 views
Status of large-scale structure formation within cosmology today
Since the CMB results of the past decade, would it be fair to say that the consensus among cosmologists is that cosmic strings are no longer considered as a (major) source for density perturbations?
...
8
votes
1answer
75 views
Biggest crater in the Solar System
It seems that the biggest crater in the Solar System is Borealis Basin on Mars. The Wikipedia entry and this piece of news say it has been formed by an impact with a body of around 1600 - ...
6
votes
1answer
82 views
What is the orbital path of Omega Centauri?
I was under the impression the only objects relatively close to our Milky Way but not yet a part of it were the Sagittarius Dwarf and Large and Small Magellanic Clouds and then much further out, but ...
3
votes
1answer
121 views
Stability of moons around tidally locked exoplanets
Can someone send me pointers to work (either theoretical or simulations)
showing (in)stability of satellite orbits around tidally locked exoplanets?
I want to know firstly if satellite orbits can ...
1
vote
1answer
298 views
Blandford-Znajek process: Why/how does the current flow along the magnetic field lines
Related: How would a black hole power plant work?
I have put a bit of commentary enumerating my confusions in parentheses
I read in Black Holes and Time Warps (Kip Thorne), that quasars can generate ...
9
votes
1answer
57 views
Introduction to neutron star physics
I enjoy thinking about theoretical astrophysics because I want to understand black holes. Given that no one understands black holes, I like to ponder the nearest thing to a black hole: a neutron star! ...
4
votes
0answers
94 views
Relation between isophotal radius and virial radius in spiral galaxies?
Is there any (proposed) relation between the B-band isophotal radius of a spiral galaxy and its virial radius (r_200)?
If you know of such a relation, please post a reference paper.
10
votes
1answer
83 views
What proportion of a star's hydrogen is consumed in its life?
I've heard in a lecture that a star like the sun would burn 3% of its Hydrogen before expiring.
I would have thought it would be much more.
3
votes
1answer
678 views
Signal-to-noise ratio of the difference between two signals
Something tells me this must be a fairly simple question, but I have somehow been unable to find an answer to it. In short: I need to calculate the difference between two signals, A and B, each one of ...
7
votes
3answers
485 views
Why doesn't helium start to fuse while there is still hydrogen fuel?
In all the descriptions of the stellar life cycle it seems as though helium doesn't start being fused until all (most?) of the hydrogen is gone.
Is this true? Why is this?
It seems counter ...
3
votes
2answers
125 views
Gravity of a disc
What proof is there that the center of gravity of a disc is at its center when the gravitational field is not uniform, such as objects close to the edge of the disc, or lying within the body of the ...
6
votes
2answers
184 views
Black hole collision and the event horizon
Will the event horizons of a two black holes be perturbed or bent before a collision? What will the shape of the event horizon appear to be immediately after first contact?
3
votes
2answers
189 views
Why is the observed signal the convolution of the true signal with the instrumental function?
Imagine we are observing a star. The light coming from a star enters an optical instrument that will give us some observed data, such as the spectrum of light say.
What we observe is not the true ...
3
votes
1answer
145 views
Why can't a stable star have radius 1 < r < 9/8 its Schwarzschild radius?
From http://www.spacetimetravel.org/ssm/ssm.html :
A mass of 1.78 [in geometric units] corresponds to a ratio of radius to Schwarzschild radius of 9/8. Theory predicts that a smaller ratio is not ...
2
votes
2answers
166 views
Can the implications of dark energy be used to bridge the gap between Quantum Mechanics and General Relativity?
Can the findings of the Physics Nobel Laureates of 2011, namely the overpowering existence of dark energy (vacuum energy) have any implications in the quest the combine Quantum Mechanics and General ...
3
votes
3answers
206 views
How scientists estimated that our universe is 4% normal matter, 21% dark matter, and 75% dark energy?
Is there a simple way to understand how scientists estimated/calculated the following percentages?
1
vote
2answers
77 views
Could a viable solar system work with a cluster of dwarf stars in center? And would it last longer than a single stellar mass star?
So, I was watching various sci channel shows, and they touch on how extremely massive stars live only 100k years, vs the sun which lives ~10 billion years, and dwarf stars live some unspecified time ...
1
vote
1answer
150 views
Supermassive Black Holes = expansion origin?
(Sorry, couldn't resist the title)
An article on Physics Today brings news that there is a new record for largest black hole (not) seen in space, some 300 million light-years away. It hints at ...
12
votes
9answers
169 views
In astronomy what phenomena have theory predicted before observations?
As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought ...
3
votes
1answer
18 views
Code to sample from & integrate light of a cluster?
Are there any publicly available codes to sample from an initial mass function (common ones... Kroupa, Chabrier, Salpeter) to construct a cluster, then use stellar models to generate an integrated ...
7
votes
1answer
173 views
How would nucleosynthesis be different if the neutron were stable?
If the strong nuclear force were just 2% stronger, the neutron would be a stable particle instead of having a half life of about 13 minutes. What difference would that have made to Big Bang ...
5
votes
6answers
550 views
Why does the earth rotate? [duplicate]
Possible Duplicate:
Why does every thing spin?
So why would the earth, or any planet for that matter, rotate along an axis? I know of no force which could come into play here, so i assume ...
3
votes
1answer
535 views
Escape velocity of a rocket standing on Ganymede (Moon of Jupiter)
I want to calculate the escape velocity of a rocket, standing on the surface of Ganymede (moon of Jupiter) and trying to leave Ganymede.
My thinking was, the kinetic energy $E_{\text{KIN}}$ must be ...
3
votes
1answer
97 views
The fine structure non-constant
If the fine structure constant is different in different parts of the universe, then what would happen if we travelled to those regions?
(I realise this is completely impossible as they are ...
4
votes
3answers
1k views
Use of advanced mathematics in astronomy, like topology, abstract algebra, or others
I know that topology, abstract algebra, K-theory, Riemannian geometry and others, can be used in physics. Are some of these areas used in astronomy, and are some astronomical theories based on them?
...
1
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0answers
83 views
What is the meaning of colors in deep space pictures? [closed]
Are the telescopes really capturing these colors in deep space or are they just "artist's impression". What could make such vast space "red" or "green"?
2
votes
0answers
91 views
Does Spacetime have a “This Side Up” arrow? [duplicate]
Possible Duplicate:
Does the curvature of spacetime theory assume gravity?
Forgive my naivete as I am not schooled in Physics or Mathematics.
I was watching NOVA's "The Fabric of the ...
7
votes
1answer
54 views
What's the most accepted theory for Blue Stragglers These Days?
I'm working on a post against a recent creationism article about blue stragglers. From when I was in undergrad, the general explanation was that they were likely second generation stars within ...
2
votes
3answers
233 views
Why every galaxy is moving away from every other galaxy on astronomical scale? because of an explosion or because of creation of space?
Why galaxies move away from each other in general on the astronomical scale?
Which answer is correct of the following?
It is because of the big bang theory, everything is just moving away from ...
2
votes
0answers
135 views
Angular Diameter, Parallax - Perceived size of Objects
I'm currently in the process of writing a 2.5D Application that should display the perceived size of an Object. For example, When I have a ball that has a diameter of 1meter, how big would it appear ...
3
votes
1answer
24 views
What happens when astronomical bodies made up of Dark Matter collapse or collide?
Does dark matter not produce heat or radiation after a collision etc?
Or, we detect radiations having no generators?
4
votes
4answers
90 views
Is dark matter around the Milky Way spread in a spiral shape (or, in a different shape)?
Dark matter doesn't interact with electromagnetic radiation, but it, at least, participates in gravitational interactions as known from the discovery of dark matter. But does dark matter exist in a ...
4
votes
1answer
41 views
How fast is the Cosmic Microwave Background Radiation (CMBR) changing?
I know that the Cosmic Microwave Background Radiation (CMBR) is the leftover radiation from the "surface of last scattering".
However, at every instant the surface is changing (at the rate of flow ...
2
votes
3answers
659 views
Initial vs Constant Orbital Velocity
I am working on some basic physics simulation for a game and need to simulate gravity. I have a system working that is behaving more or less correctly so far, but I want to see if I can send a ...
1
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3answers
263 views
What was so surprising about accelerating cosmological expansion?
The 2011 Nobel Prize in Physics, as far as I understand, concerns the expanding universe -- galaxies moving away from each other at ever increasing speed (that's what I think I read in newspapers). ...
