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.
1
vote
0answers
33 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) ...
1
vote
1answer
49 views
Optical depth in astrophysics
How can be the exponential decay of the intensity $I$ via the optical depth $\tau$ be derived?
$$I(\tau)=I(0)e^{-\tau} $$
0
votes
2answers
72 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
88 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
80 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
59 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
818 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
122 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
1answer
54 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 ...
25
votes
1answer
489 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
283 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
votes
0answers
102 views
When can a body of water glow in space?
How would superionic water be formed at the core of a giant water planet? The publication
Giant planets may host superionic water, E. Marris, Nature News, 22 March 2005,
states that water in ...
1
vote
2answers
87 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
115 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
vote
0answers
54 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
64 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
49 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
215 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
143 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
132 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
votes
1answer
62 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
vote
1answer
56 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
39 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
120 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
votes
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
115 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
157 views
Are Neutron stars transparent?
Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
7
votes
3answers
228 views
How do you explain Kepler's third law in general terms without complex math?
I understand the first law-elliptical orbits, and the second-equal area in same time, but I need help with the third one. Note that I am not in an AP course or taking calculus at the moment so simple ...
0
votes
1answer
40 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
73 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
101 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
104 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 ...
1
vote
1answer
108 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
96 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 ...
1
vote
1answer
72 views
If matter creates space, shouldn't there be experimentally detectable consequences?
Ernst Mach, a man to who influenced Albert Einstein significantly in his approach to relativity, did not quite seem to believe in space as a self-existing entity. I'm pretty sure it would be correct ...
6
votes
2answers
162 views
Is the speed of sound almost as high as the speed of light in neutron stars?
Have you ever wondered about the elastic properties of neutron stars?
Such stars, being immensely dense, in which neutrons are bound together by the strong nuclear force on top of the strong gravity ...
3
votes
1answer
51 views
How accurate are our calculations about distant stars keeping in mind their enormous distances?
Since many stars are hundreds of light years away from the earth and therefore, what we observe of them today is really their distant past, how can we say anything with certainty about their ...
6
votes
0answers
84 views
How scientists could say that such meteorite comes from Mars
How could scientists affirm that a meteorite comes from Mars and not from another source ?
This is a probability or an absolute certainty ? How much percent ?
2
votes
1answer
122 views
Can we transfer burn to another planet at any time?
Assume delta-v isn't a problem and circular orbits.
EDIT: Assume that you're already in orbit so you don't have to shift a massive load of fuel up, and the absolute ideal is something that has a ...
1
vote
2answers
152 views
Dark Matter 'Stars'
I'm aware that the Milky Way has a dark matter 'halo' around it, presumably a spherically symmetric distribution.
But I'm completely ignorant regarding the theories explaining dark matter... Is there ...
3
votes
1answer
46 views
How do the “tidal forces warming moons” theories hold when apart from heating from expansion, there may be also cooling from contraction?
I can understand a temporary heating, from the tital forces exerted on the moon but wouldn't there be cooling as well eventually when particles "give in" to contraction? Wouldn't they eventually net a ...
2
votes
2answers
86 views
Total radiation flux from a star
I'm looking around the net to find good resources on how to compute total radiation flux from a given star at a given orbiting distance.
Ideally I'd like to get not just the $W/m^2$ of the star, but ...
0
votes
2answers
80 views
Are the SI units used in astrophysics?
Just a curious question, do astrophysicist use the SI units, for example in this equation,
$r = 5pc$, will this be converted to meters?
And what does this $\nu$ stand for?
8
votes
2answers
156 views
Stellar winds from neutron stars
It seems that this question has not really been explored in the literature. Do isolated neutron stars (which do not accrete material) emit stellar wind? If yes, what composition would it have? If yes, ...
3
votes
1answer
71 views
What is the furthest object from which fermion rays were detected?
What is the furthest object from which non-electromagnetic cosmic rays were detected?
50
votes
7answers
3k views
How can a black hole produce sound?
I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the ...
4
votes
2answers
81 views
What reason(s) exist to suppose that all degeneracy pressures can be overcome in Black-Hole formation?
In models of stellar collapse to a black hole, it is a given that density increases without bound towards a singularity. Electron degeneracy I get. Neutron degeneracy I get. I assume there's some ...
1
vote
3answers
79 views
Redshift of light in dark matter
Following Edwin Hubble, it is widely believed that the universe is expanding, which is based on the red-shift of light from distant objects. Can dark matter cause light to be red-shifted and make it ...
0
votes
0answers
136 views
A book for IOAA [closed]
Hello I am preparing for the International Olympiad on Astronomy and Astrophysics. However my knowledge of constellations and practical astronomy is very poor. I was looking for a book which would ...
