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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neutrinos by formation of “neutron pairs”
Here :
http://www.newscientist.com/article/dn20084-neutron-star-seen-forming-exotic-new-state-of-matter.html
are news on superfluidity in a neutron star. The necessary bosons they say are pairs of ...
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4answers
240 views
Cosmic background radiation
Where/what is emitting cosmic background radiation, and when did it come into existance, was immediately after the big bang?
I know that the universe isn't 3D in the traditional sense, and I don't ...
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4answers
2k views
How fast is earth moving through the universe
As the galaxy is moving and the solar system orbiting the galaxy and the Earth orbiting the sun. So how fast is each object moving and what is the fastest we move at?
Do we even know how fast the ...
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2answers
348 views
Speed of sound in astrophysics
Why is the speed of sound given so much importance in Astrophysics? For example in gas outflow (and accretion) problems, we often calculate the sonic point (the point at which the outflow speed ...
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2answers
1k views
Are we living in a false vacuum? Is there any way to tell?
I was thinking of the noted 1980 paper by Sidney Coleman and Frank de Luccia--"Gravitational effects of and on vacuum decay"-- about metastable vacuum states that could tunnel to a lower energy "true ...
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1answer
259 views
How is the mass of black hole at the centre of our galaxy measured?
Ive been watching a video about dark mater and Joe al lot of the mass is missing in our universe. And astronomers got to this by measuring the speed that stars orbit he Center of the galaxy and when ...
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2answers
140 views
What is a magnetised neutron star?
I heard the term the other day, but it seems strange to me. My understanding is that neutron stars are made up of neutrons; and neutrons (having no charge) shouldn't be magnetised.
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1answer
305 views
Given temperature, composition, column density, and radial velocity, can I find the bulk flow of a gas cloud?
We've got a hot star in the middle of a gas cloud. We point a spectrometer at the star, calculating the following attributes of our line of sight at the star through the cloud:
Total number of ...
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3answers
877 views
Age of the Earth and the star that preceded the Sun
One of the great unheralded advances made in the history of science was the ability to determine the age of Earth based on the decay of isotopic uranium. Based on the apparent abundance of uranium in ...
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1answer
182 views
If Fine Structure Constant in not uniform in space what would that imply for cosmic background?
Recently J.Webb submitted paper which has extraordinary claim - that Fine Structure Constant is different in different directions in space! He (with others) measured $\alpha$ using quasar spectrum ...
2
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2answers
334 views
The source of the light we see from the Sun
Is it true that the visible light we see from the Sun comes from the electron-electron shell changes from the element iron as they absorb and emit energy in the form of photons. This energy derived ...
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0answers
84 views
launching projectiles [closed]
certainly if you calculate the maximum points in a parabolic motion for different values of angles, and join these points, the curve obtained is part of an elliptic curve. my question is: is there ...
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3answers
462 views
Evidence for black hole event horizons
I know that there's a lot of evidence for extremely compact bodies. But is there any observation from which we can infer the existence of an actual horizon?
Even if we are able to someday resolve ...
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1answer
728 views
Why do galaxies and water going down a plug hole spin?
We all experience things spinning, whether it's water down a drain, the earth on its axis, planets round the sun, or stars in a galaxy - even electrons round an atom.
But why is spin so common in ...
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1answer
260 views
Pulsar gravitational binding energy?
A Newtonian homogeneous density sphere has gravitational binding energy in Joules $U = -(3/5)(GM^2)/r$, G=Newton's constant, M=gravitational mass, r=radius, mks. The fraction of binding energy to ...
2
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5answers
786 views
Is there a black hole in the centre of the Milky Way?
Is it true that the whole galaxy is actually revolving, and powered by a black hole?
Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the ...
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6answers
2k views
How fast a (relatively) small black hole will consume the Earth?
This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth".
Consider a small black hole, that is somehow got inside the Earth. Under ...
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4answers
385 views
Is the Fine Stucture constant constant?
I have read that the fine structure constant may well not be a constant. Now, if this were to be true, what would be the effect of a higher or lower value? (and why?)
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1answer
206 views
Ground-based anti-matter detector on the cheap?
Given today's revelation of the detection of terrestrial gammay-ray flashes (TGF) produced by thunderstorms and the associated pair production of an electron and a positron, how feasible is it to set ...
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1answer
278 views
Can we measure the “Tilt-A-Whirl” effect of the Earth+Sun orbiting the galactic hub?
You've probably ridden on the fairground ride called the "Tilt-A-Whirl", or--as Disneyland calls it--the "Spinning Teacups", as well as other fairground rides that employ epicycles. You can really ...
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1answer
654 views
The Galactic Plane
I'm guessing this isn't a great physics question, but I just can't find an answer with Google.
If the galactic plane is perfectly horizontal at what angle and rotation will the ecliptic plane of our ...
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6answers
1k views
The final death of a black hole
What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and ...
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3answers
193 views
Calculating absolute speed of a relative object [closed]
Say you pick a point on the Earth. The earth spins at some constant $x (I don't know how fast, sorry). Now, that point has a different relative speed to a fixed point on Earth's orbit as it revolves ...
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1answer
169 views
Astrophysical Data
I am working on a project that requires some amount of number crunching. I require some basic data about the galaxy M82 and our own Milky Way (particularly luminosities). My advisor is a nut and he ...
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4answers
150 views
Where can we find information of International Physics/Astrophysics conferences?
Where do you check and put them usually?
Let's make a wiki ~
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1answer
117 views
How long does it take a object captured by a star falling to the center?
If the captured object do not have tangential velocity, it's just the free-fall time. But when it has, it may take longer time to fall in, right ?
The function should be
$\ddot{r} = -GM/r^2 + ...
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6answers
2k views
Why is the mapped universe shaped like an hourglass?
I've watched a video from the American National History Museum entitled The Known Universe.
The video shows a continuous animation zooming out from earth to the entire known universe. It claims to ...
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5answers
787 views
Hubble's law and conservation of energy
If all distances are constantly increasing, as Hubble's law say, then lots of potential energies of form ~$\frac{1}{r}$ changes, so how is the total energy of the Universe conserved with Hubble's ...
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2answers
346 views
Experimental observation of matter/antimatter in the universe
Ordinary matter and antimatter have the same physical properties when it comes to, for example, spectroscopy. Hydrogen and antihydrogen atoms produce the same spectroscopy when excited, and adsorb the ...
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6answers
717 views
Escape velocity
The escape velocity of earth is roughly $11 kms^{-1}$. However, what if a long ladder was built extending out of earth's atmosphere and considerably more. Then if something was to climb up at much ...
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1answer
112 views
Proposed model for existence of bar in galaxies
What are the current explanations and models for the formation of a central bar in some galaxies, and what is the difference that can produce a barred galaxy instead of a spiral one ?
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6answers
835 views
Why isn't dark matter just matter?
There's more gravitational force in our galaxy (and others) than can be explained by counting stars. So why not lots of dark planetery systems (ie without stars) ? Why must we assume some undiscovered ...
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4answers
639 views
How would I calculate celestial body characteristics without a priori knowledge?
Without any a priori knowledge of the mass, speed, distance, and size of local celestial bodies (aside from Earth's size), what can I calculate and how from my "backyard" through observation?
Edit:
...
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4answers
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How do you calculate the anomalous precession of Mercury?
One of the three classic tests of general relativity is the calculation of the precession of the perihelion of Mercury's orbit.
This precession rate had been precisely measured using data collected ...
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3answers
467 views
Energy of the electron-muon reaction
Lets see the reaction:
$e^- \mu^- \to e^- \pi^- \nu_\mu \;\;\;\;\;\;\;\;\;\;\; {(1)}$
I suppose, that this reaction occurs as follows
$e^- \mu^- \to e^- \mu^- \pi^+ \pi^- \to e^- \pi^- \nu_\mu$
Is ...
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1answer
304 views
How many atoms per light year does light encounter when traversing interstellar space?
Interstellar space is pretty empty but there a small number of of atoms (mostly hydrogen?) floating around. How many atoms per light year would a photon encounter while traversing interstellar space?
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5answers
476 views
If the size of universe doubled
My question is silly formulated, but I want to know if there is some sensible physical question buried in it:
Suppose an exact copy of our universe is made, but where spatial distances and sizes are ...
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3answers
829 views
How neutron stars burn ? Is it decay or fusion or something else?
What makes it burn, what kind of
fusion/decay is happening there ?
Another question is, what suppose to
happen with neutron star on long run ? What if it cools, then what
degenerated matter looks ...
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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
266 views
Why is it thought that normal physics doesn't exist inside the event horizon of a black hole?
A black hole is so dense that a sphere around it called the event horizon has a greater escape velocity than the speed of light, making it black. So why do astronomers think that there is anything ...
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1answer
321 views
What would be the real-world implications of the Kessler Syndrome?
I recently read about the Kessler Syndrome and am thinking about writing a story set in a world suffering from it. In the interest of realism, I am curious about the secondary effects which would be ...
3
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4answers
2k views
Planet orbits: what's the difference between gravity and centripetal force?
My physics teacher says that centripetal force is caused by gravity. I'm not entirely sure how this works? How can force cause another in space (ie where there's nothing).
My astronomy teacher says ...
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3answers
191 views
A force's magnitude
In this question I asked about gravity and in the answers it came up that the magnitude is equal (of the gravity acting on the Sun and the of the gravity acting on the Earth)
Does magnitude simply ...
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2answers
281 views
How are the northern lights produced?
Although I've never seen it myself, I hear the northern lights are a sight to be seen! I know they're related to the Earth's magnetic field but I don't know much more about them. What is the physical ...
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2answers
1k views
How does one measure the mass of a galaxy? And other such large quantities
Trained as a pure mathematician, I see claims about the mass of a galaxy and other such huge measurements that are arrived at experimentally, and I just have to scratch my head.
I know this is a bit ...
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2answers
712 views
Is it possible that all neutron stars are actually pulsars?
I'm assing that what I've been told is true:
We can only detect pulsars if their beam(s) of electromagnet radiation is directed at Earth.
That pulsars are the same as neutron stars only they emit ...
