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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is the sun itself moving

I just thought of an interesting question.Is the sun actually moving? I have learnt that the way the lunar landers and the space ships of the Mercury and Apallo missions moved and controlled their ...
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1answer
463 views

Does the long axis of Earth's orbit precess? Does it nutate?

Get up off the plane of the ecliptic by a couple of million miles. Look back at the Sun and watch the Earth's orbit in time-lapse for a few centuries. The orbit is an ellipse tilted at 23.5 degrees ...
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1answer
3k views

Star Surface Temperature Vs. Mass

I am hoping that someone can clarify this for me. With these equations. (Boltzmann Law) and radius of Radius of star how does surface temp scale with mass $R _x \approx R_\bigodot ...
3
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1answer
647 views

Hydrostatic equilibrium of a star - simplification math error

I am trying to do this question and getting stuck at interpreting what the question is asking for. $$dP/dR = -g(R)\rho(R) = -[GM(<R)/R^2]\rho(R).$$ Thus when we descend a distance $\Delta R$ ...
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3answers
344 views

Effect of expansion of space on CMB

Is it true that the expansion of space time cause the CMB to become microwaves from a shorter wavelength. If it is has the amplitude been increased? Seeing as the amplitude has decreased; why hasn't ...
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2answers
145 views

Star trace in the sky

If the space of universe is expanding at fast rates..(even faster than light) Why we do not see the trace of the stars? A possible answer could be that the stars are only moving away but mantaining ...
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2answers
364 views

What happens to internal energy in high-density materials?

Normal-density materials have internal energy, which is the sum of the average energies associated to each of the degrees of freedom. Degrees of freedom can be described as vibrational, translational, ...
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1answer
209 views

Gamma Ray Bubble at the center of our galaxy seen by Fermi Telescope

How could we measure high energy photons, whithout measuring them ? I can't understand how we can "see" those Gamma Ray Bubbles if they are not reaching here In this graph from Nasa you can see ...
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1answer
145 views

What are wimpy particles?

Can anyone give a brief overview of what a wimpy particle is?
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3answers
295 views

Expansion of space and gravity

In my previous question I asked how gravity can be represented as dents in space. It seems that it's a metaphor. But I wondered with spac expanding does the effect of gravity get bigger as well, I ...
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3answers
406 views

How does solar activity affect the ISS?

Currently the sun is launching some intense solar flares. http://www.guardian.co.uk/science/2011/feb/17/solar-flares-northern-lights-uk Th article I've linked also mentions how a "coronal mass ...
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1answer
1k views

If Betelgeuse were to go supernova

If Betelgeuse were to go supernova would the sky be twice as bright, or day time extended, depending on what time of year it happened in. Basically when it does supernova how bright and large will it ...
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1answer
575 views

History of Man Acquired knowledge of solar system [closed]

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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3answers
570 views

Space as “flat” plane

I was watching the documentary Carl Sagan did about gravity (I believe it's quite old though) and wondered about space being "flat" and that mass creates dents in this plane as shown at about 3 ...
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3answers
781 views

Black holes in a head-on collision

Assume two uncharged non-rotating black holes traveling straight at each other with no outside forces acting on the system. What is thought to happen to the kinetic energy of these two masses when ...
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1answer
929 views

How to determine velocity and mass of asteroid 2011 CQ1

As you may have seen, a small asteroid had a near miss with the earth a few days ago. As a physics teacher teaching momentum, I think this could be an excellent problem for my students, however, I ...
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2answers
264 views

What about the neutron stars with CMB temperature as dark matter?

Inspired by How do we know that dark matter is dark? and What is the temperature of the surface and core of a neutron star formed 12 billion years ago now equal to?
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3answers
154 views

Ability to detect pulsars

Am I correct it remembering that unless a pulsars beams plane faces earth we can not detect them. And that similarly inbetween the pulses we can't see them either? If so how does this differ from ...
3
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1answer
381 views

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
337 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 ...
2
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2answers
559 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
3k 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
387 views

How is the mass of black hole at the center of our galaxy measured?

I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did ...
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2answers
272 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
406 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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5answers
3k 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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2answers
508 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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3answers
762 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
2k 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
456 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 ...
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7answers
1k 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 ...
28
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6answers
4k 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 ...
11
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4answers
526 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
220 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
480 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
1k 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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4answers
724 views

What happens if a black hole sucks up a massive amount of oxygen and hydrogen?

Suppose a black hole were to suck up a massive amount of surrounding oxygen and hydrogen. Would this ignite inside the black hole and turn it back into a star?
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5answers
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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
332 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
201 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
168 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
131 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
7k 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 ...
12
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5answers
3k 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 ...
23
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2answers
612 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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1answer
128 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
2k 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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3answers
1k 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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3answers
592 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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9answers
17k views

Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...