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 dark matter around the Milky Way spread in a spiral shape (or, in a different shape)?

Dark matter doesn't interact with electromagnetic radiation, but it, at least, participates in gravitational interactions as known from the discovery of dark matter. But does dark matter exist in a ...
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2answers
343 views

How fast is the Cosmic Microwave Background Radiation (CMBR) changing?

I know that the Cosmic Microwave Background Radiation (CMBR) is the leftover radiation from the "surface of last scattering". However, at every instant the surface is changing (at the rate of flow ...
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3answers
2k views

Initial vs Constant Orbital Velocity

I am working on some basic physics simulation for a game and need to simulate gravity. I have a system working that is behaving more or less correctly so far, but I want to see if I can send a ...
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3answers
299 views

What was so surprising about accelerating cosmological expansion?

The 2011 Nobel Prize in Physics, as far as I understand, concerns the expanding universe -- galaxies moving away from each other at ever increasing speed (that's what I think I read in newspapers). ...
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0answers
137 views

Surface normal on the earth to the sun at a given point in time

How complicated is it to calculate a surface normal on the spherical approximation of the earths surface pointing towards the sun at a given point in time? What I try do is to highlight a small area ...
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2answers
630 views

Why don't stars in globular clusters all orbit in the same plane?

Globular clusters like Omega Centauri certainly don't seem to be very coplanar at all. In other words, why doesn't the explanation at Why are our planets in the solar system all on the same disc/...
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3answers
372 views

If neutrinos travel faster than light, how much lead time would we have over detecting supernovas?

In light of the recent story that neutrinos travel faster than photons, I realize the news about this is sensationalistic and many tests still remain, but let's ASSUME neutrinos are eventually proven ...
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1answer
218 views

Gravitational lensing from an extended body Vs. a point mass

I am interested in gravitational lensing caused by a cluster of galaxies (say it has a diameter of 1 Mpc and mass of $10^{12}$ solar masses). How close must a light travel as it passes by to be ...
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3answers
5k views

Why are stars, planets and larger moons (approximately) spherical in shape (like, the Sun, the Moon, the Earth, and other planets)?

Why are stars, planets and larger moons (approximately) spherical in shape (like, the Sun, the Moon, the Earth, and other planets)?
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2answers
56 views

What physical interactions actually make single stars leave their binary companions at formation?

From an interesting ScienceDaily article, I read this Before the groups of stars disperse, binary stars move through their birth sites and the group studied how they interact with other stars ...
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1answer
283 views

Axial Tilt and precession rate of exoplanets

The Earth's axis is 23.5 degrees away from othogonality to the ecliptic, and it takes about 26 000 years for it to precess fully. I have neither an intuitive sense nor the formula for precession ...
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2answers
119 views

Balmer lines and their positions

I have two stars, both of which have Balmer lines at the same wavelength positions. The depths of the Balmer lines on each star are different, and the stars are different as well. Why does this ...
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1answer
54 views

Are there Trojan family or Hilda family satellites locked in Earth's orbit?

Jupiter has many Trojan asteroids located at Lagrangian points L4 and L5 and Hilda asteroids dispersed between points L3, L4, and L5. Does the Earth have similar satellites? If so, how many?
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0answers
109 views

Are there Trojan or Hilda asteroids locked in Earth's orbit? [closed]

Jupiter has many Trojan asteroids located at Lagrangian points L4 and L5 and Hilda asteroids dispersed between points L3, L4, and L5. Does the Earth have similar asteroids? If so, how many?
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2answers
2k views

What happens to the neighboring star of a type Ia supernova?

Supernovae of type "Ia" are those without helium present, but with evidence of silicon present in the spectrum. The most accepted theory is that this type of supernova is the result of mass accretion ...
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1answer
418 views

Near-Earth supernova

There are 51 stars within 17 light years of the Earth (source). If one of these stars was to become a supernova, how would they effect the Earth? I have read the Wikipedia article Near-Earth ...
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4answers
16k views

Why are some galaxies flat?

What is the explanation for the flatness of some galaxies? (If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
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1answer
2k views

Degree of ionization and Saha equation

Say you want to calculate degree of ionization for different gases in atmosphere of a star with abundances similar to those in Sun (let's assume you only have hydrogen, helium and sodium) over the ...
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1answer
133 views

What conditions should an asteroid or comet impact need to meet in order to start an impact winter?

Is there a way to calculate if an impact from a given asteroid (say 5 miles in diameter, solid rock to which we know the mass) would start an impact winter? If yes, I would like to see a real example ...
6
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1answer
323 views

How did enough material from other dying stars accumulate to start our sun and planets?

How far apart do scientists estimate was/were the dying star(s) that supplied the elements that comprise our sun, planet, and us? With stars so far apart and expansion of space (as I understand it) ...
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1answer
605 views

Minimum number of atoms in star

I am trying to follow a derivation on this site to derive the minimum number of (hydrogen) atoms I need so that the gravitational force dominates over internal electrostatic forces. The derivation ...
6
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2answers
270 views

How can Y-dwarf stars have such a low temperature?

A recent article from NASA said they found some stars with temperatures "as cool as the human body." How is this possible? Does fusion still occur in these stars?
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3answers
2k views

How much energy does a super nova generate?

For a scene in a SciFi book, I want to know: Is it possible to estimate how much energy per m² an object would receive that hides behind an in-system planet when the sun goes nova?
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1answer
83 views

What interpretive difference is there between defining a function with or without a differential as a postfactor?

I have thought about this and looked for answers for a long time now, but I do not have any name or label for this problem, which is the reason for the long title of this question. I have come across ...
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2answers
129 views

What are some molecules stable in outer space that are unstable under terrestrial conditions?

What are some molecules stable in outer space that are unstable under terrestrial conditions? So there are many molecules that violently react on Earth because they're too charged, have unfilled ...
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1answer
197 views

Finding shortest possible rotation period

How is it possible to find the shortest possible rotation period of a pulsar from a mass and a radius?
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6answers
637 views

Are there free data available online from cosmology (or astrophysics) experiments that anyone can analyse?

One can understand a subject better in physics by trying to solve as many problems as one can from a textbook say. When it comes to experimental physics and data analysis, no book on experimental (...
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1answer
235 views

How do the day/night temperature variations of moons compare to those of their planets?

Does the planet's eclipse have a significant impact on the flux of light hitting the moon? Does tidal locking have any effect on the day-night difference of the planet?
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5answers
2k 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
46 views

What determines a progenitor's fate as a spiral or elliptical?

I was thinking about my answer to Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)? - when it occurred to me that maybe I ...
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1answer
42 views

Would the time dilation from being in low orbit around a black hole delay/slow the effects of quantum tunneling?

If quantum tunneling will cause rigid objects like rocks to rearrange their atoms into a slow-moving liquid-like state in ~10^65 years, could an object delay this fate through time dilation in a low, ...
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5answers
14k views

Stephen Hawking says universe can create itself from nothing, but how exactly?

Stephen Hawking says in his latest book The Grand Design that, Because there is a law such as gravity, the universe can and will create itself from nothing. Is it not circular logic? I mean, how ...
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3answers
22k views

What's the difference between gas and plasma?

A friend stated that stars are hot balls of gas, however we know that technically stars are plasma. Is his statement entirely incorrect? Can a plasma be considered a form of gas or should be referred ...
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1answer
155 views

Where do the bipolar jets of black holes come from?

How are they formed? And why are they so bright?
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2answers
307 views

Where does a star's angular momentum go as its spin slows down?

So we know that stars slow down as they age. But total angular momentum must be conserved. Where does that angular momentum go? The dissipation of Earth's tides somehow transfers Earth's angular ...
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1answer
1k views

At what temperature does water become a liquid on Mars? On the asteroids? And in a vacuum?

I know that I can just read off the phase diagram for water (for the surface atmospheric pressure on each object). But could there possibly be some nuances that someone might miss just from viewing ...
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0answers
164 views

Are there formulae for calculating stellar luminosity and effective temperature as a function of age? [duplicate]

Possible Duplicate: Are there formulae for calculating stellar luminosity and effective temperature as a function of age? Is there a manageable formula or set of formulas or simple algorithms ...
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3answers
6k views

Why did the asteroid belt between Mars and Jupiter form as it did?

I'm curious about why the asteroid belt wasn't pulled by Mars's or Jupiter's gravity or formed into either moons or planets. Why did it form into an asteroid belt instead?
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3answers
577 views

Are there formulae for calculating stellar luminosity and effective temperature as a function of age?

Is there a manageable formula or set of formulas or simple algorithms that approximate stellar luminosity and effective temperature (or radius) as a function of stellar age? I'm aware that accurate ...
4
votes
1answer
58 views

Is there a method to estimate the atomic yield of a supernova of a given size?

Given a supernova with stellar mass $M$, is there a theoretical method to estimating the isotope yield? If so, what processes are taken into account, and how accurate can the estimate be? Would it be ...
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1answer
853 views

What is “Strong Force” & “Weak Force” in Astronomy terms?

What is "Strong Force" & "Weak Force" in Astronomy terms?
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2answers
12k views

Is Jupiter a failed star?

In my physics lessons, my teachers have always been keen to tell my class that Jupiter is considered a 'failed star' by scientists. Is this true? In my own effort I wondered if maybe this could just ...
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1answer
131 views

How are new nebulae being created?

The nebulae we see in the night sky are forming new stars. The stars are eating up the nebulae and there is no obvious process in which those nebulae are being created to compensate for that. ...
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2answers
415 views

Is there evidence of dark matter in our galaxy?

Is there evidence of dark matter in our galaxy? How can we measure this, say, how many percent of the center of our galaxy is dark matter? I did not find the answer in the question What's Dark ...
7
votes
1answer
49 views

Temperature of WIMPs

As a dark matter candidate, what should be the temperature and kinetic energy (or also the speed) of the WIMPs (weakly interacting massive particles) to agree with the observed distribution of dark ...
7
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3answers
79 views

Cosmic background radiation vs superfluids

I've been reading a lot about superfluids lately (fluids that are cooled to such a degree that they no longer obey the standard laws of physics) in various physics journals and realized that the ...
13
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1answer
4k views

How dense are nebulae?

How functionaly dense are nebulae? Are they so sparse they are only visible from an interstellar or intergalactic perspective or would you be unable to see your hand in one? Do they vary widely in ...
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4answers
1k views

Can black holes actually merge?

If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...
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5answers
2k views

How is it possible for astronomers to see something 13B light years away?

In a NPR News story from a few years back: "A gamma-ray burst from about 13 billion light years away has become the most distant object in the known universe." I'm a layman when it comes ...
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6k views

What is the strongest evidence that anti-matter exists?

Every space show I watch mentions that anti-matter used to exist, or still does and we just can't detect it. I think some shows even say we can create a small amount of anti-matter. It is not ...