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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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
565 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
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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
293 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
298 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
350 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 ...
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4answers
4k 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
252 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 ...
10
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2answers
310 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
2k 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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3answers
1k views

Is it possible that all neutron stars are actually pulsars?

I'm assuming that what I've been told is true: We can only detect pulsars if their beams of electromagnetic radiation is directed towards Earth. That pulsars are the same as neutron stars, only that ...