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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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) ...
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1answer
49 views
Optical depth in astrophysics
How can be the exponential decay of the intensity $I$ via the optical depth $\tau$ be derived?
$$I(\tau)=I(0)e^{-\tau} $$
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2answers
73 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 ...
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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 ...
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5answers
681 views
Anti-Matter Black Holes
Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a ...
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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 ...
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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 ...
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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, ...
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1answer
55 views
Voyager 1 cosmic ray strips
In the last months Voyager 1 has experienced a dramatic drop in the cosmic ray radiation, which was been exceptionally uniform for the last 10 years, except for the past july 28 and august 14 events, ...
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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 ...
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2answers
834 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 ...
4
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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 ...
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2answers
124 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 ...
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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 ...
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1answer
105 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 ...
25
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1answer
501 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 ...
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1answer
287 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 ...
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5answers
6k views
Gravity on the International Space Station
We created a table in my physics class which contained the strength of gravity on different planet and objects in space. At altitude 0(earth), the gravitational strength is 100%. On the moon at ...
4
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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?
...
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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 ...
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2answers
116 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: ...
5
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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 ...
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2answers
65 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 ...
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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 ...
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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
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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 ...
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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?
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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 ...
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2answers
409 views
How was the Oh-My-God particle observed?
How exactly was the Oh-My-God particle (ultra-high energy cosmic ray) observed and its energy measured?
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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 ...
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3answers
121 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 ...
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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
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1answer
118 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 ...
2
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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 ...
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2answers
264 views
What is the temperature of the surface and core of a neutron star formed 12 billion years ago now equal to?
In what part of the spectrum is it radiating? In the infrared, in the microwave? Or is not radiating anymore at all?
In russian:
Чему сейчас равна температура поверхности и ядра нейтронной звезды, ...
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3answers
158 views
Are Neutron stars transparent?
Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
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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 ...
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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 ...
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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?
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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
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2answers
104 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 ...
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1answer
538 views
When will the Moon reach escape velocity?
From what I know, the Moon is accelerating away from the Earth. Do we know when it will reach escape velocity? How do we calculate this?
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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 ...
3
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5answers
1k views
How do we know that earth moves around sun and that too in elliptical orbit
I know the basics of solar system like how earth moves around sun, and that we have so many planets, elliptical orbit of earth, and how far is sun from earth etc etc. I want to take a step back and ...
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6answers
513 views
Why is there an escape velocity?
I've been trying for days, but I just can't understand why escape velocities exist. I've searched the web and even this site, and although I've read many explanations, I haven't been able to truly ...
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2answers
164 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 ...
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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 ...
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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 ...
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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.
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487 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 ...
