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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2answers
67 views
Why polar jets emited along axis of rotation?
why streams of energy-matter are emited along the axis of rotation of a compact object?
(or) what is the reason that they are emited along the axis of rotation of a compact object?
0
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0answers
22 views
Spherically-symmetric Pressure free Collapse [closed]
How to show-"zero pressure and spherical symmetry implies that a point on the surface follows a radial timelike geodesic"?
0
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0answers
26 views
Relation between the period of rotation and the period of revolution of a satellite
I read somewhere that the tidal forces between the earth and the moon causes the equality between the 2 periods of the moon and that every planet-satellite system will evolve to this condition (like ...
0
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1answer
26 views
Power radiated by a star, black body model
let's say I want to model a star of radius $R$ at a distance $r$ from the Earth. I need to show that the apparent luminosity for frequency $\nu$ is equal to
$$\ell(\nu)=\frac{2\pi h}{c^2}\left( ...
1
vote
1answer
43 views
Relationships between different measure of opacity
I'm reading some papers that compare different values for a materials opacity to a particular particle. The first is given as $\frac{dE}{dX}$, a single particles energy loss per unit column depth (X ...
4
votes
2answers
156 views
How to cut a stone on on a White Dwarf
I've heard that white dwarfs are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
0
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0answers
18 views
laser wave functions excitation state change question
Supposing an Einstein-Bose condensate where electrons are excited to the point of coherent light emiting.
Regarding lighwave coherence:
* Does the exitation state make the coherence itself ...
1
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1answer
38 views
Dimensions of a variable celestial body?
I read (extern link to a filehoster, page 163 section 4.8) that a variable celestial object like a pulsar or quasar must be smaller than the distance the light travels in its variation period.
Can ...
6
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1answer
129 views
Do any stars exist apart from galaxies?
Do any stars exist apart from galaxies? Do "maverick" stars exist?
-1
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0answers
48 views
Peculiar velocity, galactic superclusters and dark energy? [closed]
So I've stumbled upon some information regarding the existence of this "peculiar velocity" and as I have very limited knowledge of astronomy/astrophysics and a hunger for knowledge, but no idea where ...
1
vote
2answers
70 views
starlight flux on earth
I want to calculate if it is possible to photograph a subject lit only by starlight. I found one website claiming that a starlit scene is lv = -15 (daylight is lv 15, or 2^31 times brighter), but he ...
5
votes
1answer
64 views
Astronomical-wavelength radio (AWR) transmissions between cosmic plasmas?
My son asked me if electromagnetic waves longer than radio exist. I told him that even though physics permits such waves, there are no antennas long enough to radiate or detect them.
However, on ...
1
vote
1answer
43 views
Function for heating of a planet by its star
I'm looking for an algorithmic model which will gives rough estimate of the average temperature of a planet's atmosphere (good enough to say whether there will be liquid water anywhere, or if metals ...
1
vote
2answers
43 views
Spread and direction of the cosmic background radiation
Something I can never understand is that where the cosmic background radiation spreads?
If I know well, the cosmic background radiation is actually the light of the Big Bang. If it happened exactly ...
2
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0answers
45 views
Calculate large and small frequency separation for the Sun [migrated]
I want to determine the big and small frequency seperation from timeseries data for the sun. An excerpt of the data (timeseries and power series) is plotted below.
The power series is calculated in ...
0
votes
0answers
24 views
Hydrostatic equilibrium in a cylindrical area
Consider a cylinder (height $dr$, base area $dA$) with the base of the cylinder at a distance $r$ from the center of the sun.
Density = $\rho(r)$
$Volume V = base\ area\ .\ height\ = dr.dA$ (How ...
3
votes
0answers
40 views
Modeling the formation of a stellar system and matter accretion
I am trying to figure out what do I need to know to properly simulate the creation of a solar system from a particle cloud with random distribution of hydrogen atoms.
Being more of a programming ...
1
vote
0answers
38 views
Solar sail area going to Proxima Centari [closed]
I have a physics question that I need some help with:
"Proxima Centauri is a star in the Alpha Centauri solar system, it’s the
nearest star to our sun (4.24light−years) ...
2
votes
1answer
65 views
Optical depth in astrophysics
How can be the exponential decay of the intensity $I$ via the optical depth $\tau$ be derived?
$$I(\tau)=I(0)e^{-\tau} $$
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2answers
83 views
What is our estimated running speed on Moon's surface?
I was wondering if we have the chance to run on the Moon's surface, how would you expect it look like?
I expect our velocity will increase for the same work we do on Earth, but not sure if this will ...
0
votes
2answers
94 views
What if the antimatter in the center of our galaxy could annihilate and cause a chain reaction?
Being said that the antimatter - matter reaction is faster than that of a fission and fusion, what if the antimatter cloud found at the center of our galaxy could really able to react with matter from ...
0
votes
1answer
86 views
Is the underlying pattern of all dynamical physical processes in the universe actually chaotic? [closed]
After studying and pursuing research interests in chaos theory since the mid-1980s, I have to question whether standard physics (including all physical theories we currently use at all scales of size ...
4
votes
1answer
68 views
How would gravity change on a planet rotating around itself very fast?
Let's take a planet identical to Earth, but with rotation speed multiplied by ten thousand. What would happen with the gravity if it was spinning madly around itself? Would the centrifugal force make ...
24
votes
2answers
1k views
Why does a supernova explode
This is really bugging me. When you look up some educational text about stars life, this is what you find out:
Gravity creates the temperature and pressure to start fusion reactions.
The fusion ...
6
votes
2answers
137 views
What stabilizes neutorns against beta decay in a neutron star?
Free neutrons are known to undergo beta decay with a half-life of slightly above 10 minutes. Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of ...
5
votes
3answers
89 views
How is the distance to a $\gamma \mathrm{-ray}$ burst (GRB) measured in just a few days?
Recently the Fermi Gamma-ray Space Telescope recorded the most energetic Gamma Ray burst (GRB 130427A) yet observed with a peak $\gamma \mathrm{-ray}$ energy of $94\, \mathrm{GeV}$. Various sources ...
26
votes
1answer
568 views
Neutrinos vs. Photons: Who wins the race across the galaxy?
Inspired by the wording of this answer, a thought occurred to me. If a photon and a neutrino were to race along a significant stretch of our actual galaxy, which would win the race?
Now, neutrinos ...
16
votes
1answer
307 views
Where do high-energy neutrinos come from?
Last week the IceCube South Pole Neutrino Observatory published a press release reporting the possible discovery of two neutrinos with energies of over 1 PeV.
Would anyone here be willing to help me ...
1
vote
2answers
103 views
What happens when a star undergoes gravitational collapse?
Immediately prior to becoming a supernova the core of some types of stars may suffer gravitational collapse.
What happens to any planets in orbit around the star at the instant the mass is fully ...
2
votes
2answers
156 views
How long does a supernova last?
Just what the title indicates.
Is a supernova over instantaneously? Or, does the (for want of a better word) explosion continue for a while? What is/are the order of timescales involved?
EDIT: ...
1
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0answers
87 views
Could Voyager 1 have entered a solar radiation belt?
We currently believe that the Sun has no radiation belts because the unstable magnetic field, which turns every 11 years, is not stable enough to sustain a solar radiation belt. But observations from ...
5
votes
2answers
72 views
How do interstellar hydrogen atoms form stars?
I would like to learn the basics about how interstellar matter contracts into stars under the influence of gravity.
Some of my questions:
Let's assume an ideal and infinite large cloud of equally ...
0
votes
2answers
52 views
Has anyone studied a statistical scaling law for the universe? [closed]
How do named objects in the universe scale? Is there a predictable curve for an ordered list, say {atom, animal, planet, solar system, galaxy, etc}? Can you then use the analysis to predict when the ...
5
votes
3answers
225 views
We're all star dust?
OK so we've all heard of this from Carl Sagan, Lawrence Krauss and others and we know the argumentation, I don't refute that. There are other examples, for instance I once calculated (this was before ...
3
votes
1answer
160 views
How does a star ignite?
I remember reading that X-Rays are generated by 'braking' electrons in a Coolidge tube.
Is it fundamentally a matter that the extreme gravity immediately before a star ignites is so strong that it ...
3
votes
2answers
137 views
Could a planet sized bubble of breatheable atmostphere exist?
I'm reading a book (Sun of Suns by Karl Schroeder) that the main location is a planet called Virga, which contains air, water, and floating chunks of rock, and has no or a very small amount of ...
0
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1answer
64 views
What would be the effect of an excess of up quarks on stellar formation?
Suppose you had 80% up quarks, and only 20% down quarks. How would this affect stellar formation?
1
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1answer
58 views
White Dwarf radius
So I've been reading this about white dwarves, and various other sites about white dwarves. In all of them, they say that we can find the radius of a white dwarf by minimizing its total energy. I know ...
3
votes
1answer
42 views
Resources in space, and their distribution
I'm making a video game in which the economics of an interstellar civilization is important.
What I'm wondering is, how are resources in space distributed?
Since everything ultimately comes from ...
-1
votes
3answers
134 views
What cosmic event would cause Sun rising from the west?
I'm wondering what kind of astronomical or geological events would cause the reversal of Earth's rotation. For instance, Is a meteorite passing very close to Earth able to reverse its rotation?
Can ...
0
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1answer
38 views
Conversion of a star
I need to know what would happen to a star that has size 2 times the solar mass. I guess it would either be a neutron or red giant. Is that right?
6
votes
1answer
132 views
What is the frequency of occurrence of stellar classifications off the HR main-sequence?
An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
7
votes
3answers
162 views
Are Neutron stars transparent?
Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
0
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1answer
44 views
Initial separation of neutron star/black hole binaries?
How would I go about finding the distribution of initial separations (i.e. the lengths between the centres of mass) of stars that make up binary systems. I am interested in neutron stars and stellar ...
2
votes
2answers
79 views
Magnetic Pole Emission from Pulsars
I've been reading up on some pulsar emission theory (admittedly written in the 70's and 80's, but I figured that's a good place to start), namely this review by Curtis Michel as well as the book Black ...
2
votes
1answer
37 views
Reconciling Units in Jeans' Criterion Formula
In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as:
$\frac{GmM}{R_c} = \frac{3mkT}{2}$
... To me this suggests that on the left we have Joules, and on the right we have ...
3
votes
2answers
119 views
Why is the dark matter density profile within the solar radius (and local density) uncertain?
It seems that we know the rotation curve inside the sun's galactic orbit fairly accurately. Then wouldn't we be able to just take the derivative* of this to get the DM density profile at smaller ...
0
votes
1answer
135 views
Do all black holes spin in the same direction?
My question is as stated above, do all black holes spin the same direction?
To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
2
votes
1answer
112 views
In Klein-Gordon, why should infinite downwards photon cascades be possible?
Here is a simple point about the standard interpretation of the Klein-Gordon equation that for the life of me I've never been able to understand:
Why would the existence of true negative energy ...
2
votes
1answer
100 views
What are we all falling towards?
One meteorite fell on the ground in Russia, last week. In different circumstances, it could have orbited the earth, or perhaps pass close to the earth and then disappear into the space.
It seems that ...
