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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173 views
How would nucleosynthesis be different if the neutron were stable?
If the strong nuclear force were just 2% stronger, the neutron would be a stable particle instead of having a half life of about 13 minutes. What difference would that have made to Big Bang ...
12
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9answers
169 views
In astronomy what phenomena have theory predicted before observations?
As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought ...
4
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2answers
660 views
Origin of elements heavier than Iron (Fe)
In all the discussions about how the heavy elements in the universe are forged in the guts of stars and especially during a stars death, I usually hear that once the star begins fusing lighter atoms ...
3
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1answer
18 views
Code to sample from & integrate light of a cluster?
Are there any publicly available codes to sample from an initial mass function (common ones... Kroupa, Chabrier, Salpeter) to construct a cluster, then use stellar models to generate an integrated ...
7
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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 ...
6
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0answers
84 views
How scientists could say that such meteorite comes from Mars
How could scientists affirm that a meteorite comes from Mars and not from another source ?
This is a probability or an absolute certainty ? How much percent ?
3
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1answer
51 views
How accurate are our calculations about distant stars keeping in mind their enormous distances?
Since many stars are hundreds of light years away from the earth and therefore, what we observe of them today is really their distant past, how can we say anything with certainty about their ...
6
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1answer
59 views
Where do the bipolar jets of black holes come from?
How are they formed? And why are they so bright?
2
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1answer
122 views
Can we transfer burn to another planet at any time?
Assume delta-v isn't a problem and circular orbits.
EDIT: Assume that you're already in orbit so you don't have to shift a massive load of fuel up, and the absolute ideal is something that has a ...
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2answers
152 views
Dark Matter 'Stars'
I'm aware that the Milky Way has a dark matter 'halo' around it, presumably a spherically symmetric distribution.
But I'm completely ignorant regarding the theories explaining dark matter... Is there ...
4
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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
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1answer
267 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 ...
11
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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 ...
2
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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
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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 ...
3
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1answer
52 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.
...
3
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1answer
46 views
How do the “tidal forces warming moons” theories hold when apart from heating from expansion, there may be also cooling from contraction?
I can understand a temporary heating, from the tital forces exerted on the moon but wouldn't there be cooling as well eventually when particles "give in" to contraction? Wouldn't they eventually net a ...
9
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1answer
789 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
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 ...
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3answers
79 views
Redshift of light in dark matter
Following Edwin Hubble, it is widely believed that the universe is expanding, which is based on the red-shift of light from distant objects. Can dark matter cause light to be red-shifted and make it ...
2
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2answers
86 views
Total radiation flux from a star
I'm looking around the net to find good resources on how to compute total radiation flux from a given star at a given orbiting distance.
Ideally I'd like to get not just the $W/m^2$ of the star, but ...
8
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4answers
254 views
Can a moon have another large body as a satellite, and are there any examples of such?
In my mind, I'm comparing it to the Sun-Earth-Moon system. After all, the Earth is primarily a satellite of the Sun, but the Moon is still gravitationally bound to the Earth. Could something like this ...
0
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2answers
80 views
Are the SI units used in astrophysics?
Just a curious question, do astrophysicist use the SI units, for example in this equation,
$r = 5pc$, will this be converted to meters?
And what does this $\nu$ stand for?
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2answers
65 views
Recommend good book(s) about the “scientific method” as it relates to astronomy/astrophysics?
I am interested in astronomy/astrophysics, but I am not science major (I am a computer science graduate). Facts and results of the field are presented to the public without showing how these ...
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3answers
709 views
Why is planet CFBDSIR2149-0403 hot?
According to a BBC report
Astronomers have spotted a "rogue planet" - wandering the cosmos without a star to orbit - 100 light-years away.
...
The proximity of the new rogue planet has ...
7
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3answers
81 views
How would two equally massed stars orbit?
In an empty universe, except for two equally massed stars, how would they orbit? Or, for another example, if the earth suddenly grew to be the mass of the sun, how would they orbit, or interact? Would ...
4
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1answer
132 views
What day/night cycles, climate and seasons would experience Alpha Centauri Bb inhabitants?
Alpha Centauri Bb is an exoplanet orbiting Alpha Centauri B. It is asserted that given the close distance to the star the planet should be tidally locked.
The orbiting period of the planet is about ...
12
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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 ...
50
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7answers
3k views
How can a black hole produce sound?
I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the ...
42
votes
5answers
2k views
Is there a small enough planet or asteroid you can orbit by jumping?
I just had this idea of orbiting a planet just by jumping and then flying upon it on its orbit kind of like superman. So,
Would it be theoretically possible or is there a chance of that small body to ...
4
votes
2answers
81 views
What reason(s) exist to suppose that all degeneracy pressures can be overcome in Black-Hole formation?
In models of stellar collapse to a black hole, it is a given that density increases without bound towards a singularity. Electron degeneracy I get. Neutron degeneracy I get. I assume there's some ...
3
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1answer
70 views
Does the spectrum of Sol's emission change as it ages?
A follow-up to my earlier question How would one navigate interstellar space? that just occurred to me; albeit on a different tack.
Sol is probably in a state of continuous flux. The change of state ...
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0answers
136 views
A book for IOAA [closed]
Hello I am preparing for the International Olympiad on Astronomy and Astrophysics. However my knowledge of constellations and practical astronomy is very poor. I was looking for a book which would ...
6
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1answer
56 views
Is it possible to determine astronomically/astrophysically whether other planets have ever encountered polarity reversal?
We know of geomagnetic flip in Earth's history by studying geologic data. Given other planets in the system also possess a magnetic field leads to the assumption that such polarity reversal may not be ...
2
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1answer
125 views
How does one measure Earth's speed of revolution around the sun?
I know that there are several formulae that one can plug numbers into to arrive an estimate of Earth's speed around the sun (Kepler's third law for instance), but I'm wondering how these things are ...
4
votes
4answers
90 views
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 ...
4
votes
1answer
41 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 ...
6
votes
1answer
71 views
Does a celestial system exhibit a collective magnetic field?
Sol exhibits a magnetic field, most of the planets in orbit around Sol exhibit a magnetic field - strong and weak both.
Does the solar system as a whole exhibit a magnetic field?
Does the paradigm ...
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
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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 ...
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1answer
130 views
How to calculate gravity inside the star?
Gravity must decrease due to less effective mass when going inside the object but also must increase with depth inside the star due to its higher density. Is there a model or formula approximating ...
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0answers
81 views
Mass loss rate of planetary nebulae
The “interacting wind” model of planetary nebulae is based on the idea that the white dwarf phase of stellar evolution is preceded by a red giant phase. A fast wind from the hot white dwarf overtakes ...
17
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8answers
986 views
Why are L4 and L5 lagrangian points stable?
This diagram from wikipedia shows the gravitational potential energy of the sun-earth two body system, and demonstrates clearly the semi-stability of the L1, L2, and L3 lagrangian points. The blue ...
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?
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1answer
114 views
Does diffraction contribute to the Black Drop effect?
Two reasons are given to explain the black drop effect here, but I think I came up with a third.
Consider a two-dimensional cross section of the situation just after second contact and just before ...
5
votes
2answers
383 views
Do the stars imaged by a telescope even exist at present?
I know that we now have telescopes which can capture the images of the stars and galaxies millions of light-years away from us.
Does the telescope capture the past image of the star, i.e. the light ...
0
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0answers
90 views
Theoretical early-universe cosmology [closed]
I wanted to know what are the cutting edge/recent papers to read w.r.t theoretical early universe cosmology.
I would like to know of recent review papers
I would like to know of areas which use ...
3
votes
1answer
94 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?
3
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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 ...
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0answers
72 views
Does quantum Zeno effect play role in astrophysics?
For example, do two galaxies situated in proximity reduce the atom decay rate in each other?
What happens with decay quanta escaped to infinity? Does the radius of apparent horizon effect the ...
