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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1answer
126 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 ...
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0answers
91 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 ...
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 ...
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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 ...
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1answer
47 views
Could an NEO strike the moon with sufficient velocity for the shrapnel to escape Lunar gravity, and be attracted by Earth's?
Between the news item of an asteroid giving Earth a close shave, and another news item of the impending GRAIL impact ; I find myself wondering whether a NEO could be a hazard to Earth via the moon. ...
4
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4answers
261 views
Are galactic stars spiraling inwards?
Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit?
And if we are heading towards the center then what is the rate of this process?
I started ...
8
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1answer
55 views
Voyager 1 cosmic ray strips
In the last months Voyager 1 has experienced a dramatic drop in the cosmic ray radiation, which was been exceptionally uniform for the last 10 years, except for the past july 28 and august 14 events, ...
4
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1answer
160 views
Photons arriving from the Sun
Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
42
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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 ...
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2answers
29 views
How does spectroscopy determine what depth of the remote atmosphere a particular gas is at?
This article mentions "...there is less methane than expected in the upper atmosphere" of an exoplanet.
How does spectroscopy determine what depth of the atmosphere a particular gas is at? Is it a ...
5
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2answers
216 views
Do black holes have infinite areas and volumes?
How to calculate the area / volume of a black hole?
Is there a corresponding mathmetical function such as rotating 1/x around the x-axis or likewise to find the volume?
4
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1answer
89 views
NGCC 1277— a recoil ejection?
Recent calculations agree that a merging pair of supermassive black holes can emit enough gravitational waves to eject themselves from a galaxy.
Could NGCC 1277, a small galaxy with a 17 billion ...
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2answers
168 views
Does the Chandrasekhar Limit scale for a Black Hole?
No physicist/astrophysicist I; All I know about the Chandrasekhar limit is that it apparently limits the mass a star may survive, beyond which it degenerates to a neutron star, or a black-hole.
Does ...
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2answers
410 views
How was the Oh-My-God particle observed?
How exactly was the Oh-My-God particle (ultra-high energy cosmic ray) observed and its energy measured?
5
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5answers
230 views
How is distance measured to far away stars and galaxies?
What I need is an accurate description of the methods used to determine the distance to Andromeda. The Parallax method is for nearby objects as I presume. The red shift method applies, but how do you ...
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1answer
185 views
Artificial planetary magnetic field
I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need?
The question is inspired by thinking about possible colonization of ...
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2answers
829 views
What are good books for graduates/undergraduates in Astrophysics?
There are no book recommendations for Astrophysics here. I will write my own answer, but I am also interested in what are others' views on the question (I will NOT mark my own answer as the best one).
...
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1answer
86 views
If the observable universe keeps expanding would we eventualy see light 24/7… clouds permiting?
If we can see more observable universe could there be a time when day and night looked the same?
3
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1answer
83 views
What is the maximum mass of planet HD 40307 g
Recently discovered planet HD 40307g around HD40307 Star system is claiming that its inside a habitual zone of a solar system. Besides It has water where life could be evolved.
I tried to calculate ...
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1answer
63 views
Böotes Void and Dark Galxies
Wouldn't it be possible that Böotes Void, a space we generally consider to be "empty" be filled with a number of undetectable dark galaxies?
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2answers
68 views
A thought about Quasars
If Quasars are "beams" of energy exiting a super-massive black hole, in order for them to get through the black-hole's event horizon, they'd have to be traveling faster than the speed of light. My ...
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1answer
131 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 ...
7
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3answers
713 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 ...
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0answers
49 views
Why does $H_2$ form on such a long time scale?
If we were trying to figure out the time scale for a gas-phase reaction between two hydrogen atoms in a molecular cloud (which has density $~10^4/$cm$^3$), apparently the reaction would happen on a ...
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4answers
109 views
How do black holes accrete mass?
Thanks to time dilation, a distant observer watching a man fall in to a black hole will only see him asymptotically approach the event horizon. So how do black holes ever get bigger?
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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 ...
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1answer
164 views
Trying to link Eulerian and Lagrangian perturbations
I'm trying to make sense of the link between a (linear) Eulerian (i.e., at a given point) and Lagrangian (following a fluid element) perturbation. I will here express not only where I'm stuck, but ...
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1answer
341 views
Why are the orbits of the planets in our solar system along the same basic plane? [duplicate]
Possible Duplicate:
Why are our planets in the solar system all on the same disc/plane/layer?
After watching this video I realized that the orbits of the planets in our solar system ...
4
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1answer
168 views
When and How far out will the Voyager twins come to a full-stop?
So space is mostly, but not entirely, empty. Every few (dunno the order) cubic metres of space there is some cosmic dust.
Assuming that
Cosmic dust exerts some friction on passing bodies,
The ...
5
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2answers
94 views
Why is the gas halo of the Milky Way so hot?
I have read on the webpage of NASA that there is a massive hot gas halo around our galaxy. Its temperature is between 100,000 and 1 million Kelvins or more. I do not understand why is it so hot. The ...
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2answers
278 views
Why is Larry Niven's Ringworld Unstable?
In his 1970 science fiction novel Ringworld, author Larry Niven describes the eponymous Ringworld, a gigantic structure shaped as a ring with a radius of around 1 AU, rotating around a star in the ...
3
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1answer
93 views
What would happen in the final days of the universe?
I would like to know the stages of how the universe would end and what would happen and what the possible scenarios are.
I understand that eventually all the stars would burn out and that would ...
3
votes
1answer
141 views
Why are black hole singularities stable?
The Friedmann equations says that huge matter densities lead to huge expansion rates. In Newtonian gravity, two massive point particles separated by an infinitesimal distance will experience an ...
8
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2answers
499 views
What is the physical size of a black hole?
Something that's always confused me. How large is a black hole's physical size - not mass?
From descriptions, it would seem that the 'singularity' is a single point, but is it really?
Say for ...
3
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1answer
368 views
What would it be like if we had a planet very close to us?
My desktop background rotates through a bunch of space and nature scenes, and this one came up.
What would be the effect on people walking around down here, if another earth was looming overhead ...
3
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2answers
98 views
Why is NASA interested in Gamma ray bursts?
Gamma-ray bursts(GRBs) are flashes of gamma rays associated with extremely energetic explosions
why nasa interested to Gamma ray burst?
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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1answer
84 views
How is retrograde motion explained in Tycho's model?
Tycho proposed a model of the solar system where all planets but Earth move around the sun while the sun and the moon move around the earth.
I wonder how this model could explain the retrograde ...
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2answers
77 views
Is the magnetic field of a white-dwarf merely residual?
Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures?
Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ...
5
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2answers
76 views
How does Sol's magnetic field continue to exist at such high temperatures?
The temperature at the surface of Sol is apparently well above 5000C; I'm assuming the layers beneath the surface may be even hotter.
At school we learnt heating a metal beyond a certain temperature ...
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8answers
995 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 ...
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0answers
81 views
Is the fuel burn for a satellite launch affected by the position of the moon relative to the launch site?
The gross mass of a satellite rocket is tiny compared to that of Earth, and Luna. Between them, however, the two bodies set up tides in bodies of water which itself is again considerable mass.
At ...
8
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2answers
131 views
Why and how will we be able to image extraterrestrial planets in the next two decades?
According to a recently published article, a well-established Cambridge astrophysicist stated that:
the “origin of life, where it exists, and whether aliens exist,
is going to be crucial over ...
8
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6answers
514 views
Why is there an escape velocity?
I've been trying for days, but I just can't understand why escape velocities exist. I've searched the web and even this site, and although I've read many explanations, I haven't been able to truly ...
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1answer
39 views
The radius of the swept up shell of the observed planetary nebula [closed]
The emission from this shell produces the observed planetary nebula.
Assume that the fast wind switches on instantaneously at the end of the red giant phase at $t = 0$. The mass of swept up material ...
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2answers
69 views
What is the Schechter luminosity function's domain of support?
I'm trying to fit a Schechter luminosity function to some data points, but it's not clear from this definition what the domain of support of the PDF should be. I'm familiar with the standard Pareto ...
3
votes
1answer
106 views
Official definition of astronomical units
As it is relatively easy to find an official value for a large number of physical constants, (thanks to CODATA), it is not so easy for some units widely used in astronomy (Wikipedia, Google and IAU ...
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0answers
55 views
Space-time & solar mass
Does the space-time curvature described by Einstein have any affect on the accuracy of our determination in the age of a star or globular cluster? How does this affect our interpretion of how old we ...
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6answers
835 views
How close can spaceship get to the Sun
If you want to fly a spaceship with human passengers as close to the Sun as possible, then what effects would the spaceship have to be designed to counteract in order to keep the passengers alive and ...
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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 ...
