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.
12
votes
7answers
15k views
Is Melancholia's orbit impossible?
In the recent movie "Melancholia", a planet, also called Melancholia, enters the solar system and hits the Earth. I want to leave aside the (also unreasonable) aspect that planet "hides behind the ...
12
votes
1answer
88 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 ...
12
votes
3answers
91 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 ...
5
votes
1answer
146 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 ...
12
votes
3answers
423 views
Why are most astronomy things spherical in the shape (like, the Sun, the Moon, the Earth, and other planets)?
What is the reason for all the astronomy things being spherical in the shape (like, the Sun, the Moon, the Earth, and other planets)?
3
votes
0answers
206 views
Why mostly all the astronomy things are Round in the shape (like, Sun, Moon, Earth, & other planets)? [closed]
Why mostly all the astronomy things are sphere in the shape (like, Sun, Moon, Earth, & other planets)?
2
votes
2answers
19 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
...
6
votes
1answer
75 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 ...
3
votes
2answers
78 views
Balmer lines and their positions
I have two stars, both of which have Balmer lines at the same wavelength positions.
Why does this pattern exist?
6
votes
1answer
35 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?
2
votes
0answers
93 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?
7
votes
5answers
2k 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 ...
2
votes
1answer
619 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 ...
6
votes
1answer
54 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 ...
5
votes
1answer
125 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) ...
6
votes
1answer
216 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 ...
4
votes
2answers
68 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?
2
votes
3answers
371 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?
2
votes
1answer
60 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 ...
2
votes
2answers
72 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 ...
0
votes
1answer
131 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?
3
votes
6answers
194 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 ...
3
votes
1answer
93 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?
10
votes
5answers
676 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 ...
3
votes
1answer
26 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 ...
11
votes
2answers
3k views
How Earth communicates with Voyager I?
After taking a basic signals & systems class and learning about the frequency domain, I started wondering:
How the heck do scientists still communicate with Voyagers I and II??
Do they ...
2
votes
1answer
15 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, ...
8
votes
5answers
3k 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 ...
8
votes
2answers
4k 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 ...
6
votes
1answer
59 views
Where do the bipolar jets of black holes come from?
How are they formed? And why are they so bright?
4
votes
2answers
95 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 ...
2
votes
1answer
260 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 ...
2
votes
0answers
162 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 ...
2
votes
2answers
168 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
19 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 ...
1
vote
1answer
285 views
What is “Strong Force” & “Weak Force” in Astronomy terms?
What is "Strong Force" & "Weak Force" in Astronomy terms?
13
votes
1answer
3k 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 ...
3
votes
1answer
51 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.
...
11
votes
2answers
153 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 ...
6
votes
1answer
14 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
votes
3answers
32 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 ...
9
votes
1answer
784 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 ...
7
votes
3answers
672 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 ...
7
votes
4answers
489 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 ...
9
votes
4answers
853 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 ...
9
votes
2answers
307 views
How can a Population III star be so massive?
How can a Population III star have a mass of several hundred solar masses? Normally the limit is about 100 solar masses.
0
votes
1answer
546 views
Why it is said that Universe is an isolated system?
I have read in many places
"Entropy of an isolated systems never
decreases"
And as a corollary:
"As Universe is an isolated system(I) then its entropy is constantly increasing(II)"
I) ...
1
vote
1answer
193 views
Mass of a galaxy via Luminosity [closed]
Is there a way of calculating the mass of a galaxy, or even a nebula from the luminosity?
EDIT
I'm deleting this, and moving the question to Astronomy Stack Exchange - thanks david
6
votes
1answer
22 views
Lack of exoplanet missions in the decadal survey
In recent exoplanet meeting "The Next 40 Years of Exoplanets", there was much discussion of the inablity of the community to agree on whether to support coronagraph missions or interferometer ...
5
votes
3answers
77 views
Could dark energy be the effect of gravity at great distances?
This may be a silly question, but is it possible that dark energy and gravity are related to each other?
Space-time is deformed everywhere in space by objects with mass. The more massive the object, ...
