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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What would be the effect of an excess of up quarks on stellar formation?

Suppose you had 80% up quarks, and only 20% down quarks. How would this affect stellar formation?
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73 views

White Dwarf radius

So I've been reading this about white dwarves, and various other sites about white dwarves. In all of them, they say that we can find the radius of a white dwarf by minimizing its total energy. I know ...
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57 views

Resources in space, and their distribution

I'm making a video game in which the economics of an interstellar civilization is important. What I'm wondering is, how are resources in space distributed? Since everything ultimately comes from ...
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3answers
376 views

What cosmic event would cause Sun rising from the west?

I'm wondering what kind of astronomical or geological events would cause the reversal of Earth's rotation. For instance, Is a meteorite passing very close to Earth able to reverse its rotation? Can ...
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46 views

Conversion of a star

I need to know what would happen to a star that has size 2 times the solar mass. I guess it would either be a neutron or red giant. Is that right?
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370 views

What is the frequency of occurrence of stellar classifications off the HR main-sequence?

An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
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244 views

Are Neutron stars transparent?

Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
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62 views

Initial separation of neutron star/black hole binaries?

How would I go about finding the distribution of initial separations (i.e. the lengths between the centres of mass) of stars that make up binary systems. I am interested in neutron stars and stellar ...
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145 views

Magnetic Pole Emission from Pulsars

I've been reading up on some pulsar emission theory (admittedly written in the 70's and 80's, but I figured that's a good place to start), namely this review by Curtis Michel as well as the book Black ...
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48 views

Reconciling Units in Jeans' Criterion Formula

In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as: $\frac{GmM}{R_c} = \frac{3mkT}{2}$ ... To me this suggests that on the left we have Joules, and on the right we have ...
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262 views

Why is the dark matter density profile within the solar radius (and local density) uncertain?

It seems that we know the rotation curve inside the sun's galactic orbit fairly accurately. Then wouldn't we be able to just take the derivative* of this to get the DM density profile at smaller ...
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419 views

Do all black holes spin in the same direction?

My question is as stated above, do all black holes spin the same direction? To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
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176 views

In Klein-Gordon, why should infinite downwards photon cascades be possible?

Here is a simple point about the standard interpretation of the Klein-Gordon equation that for the life of me I've never been able to understand: Why would the existence of true negative energy ...
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118 views

What are we all falling towards?

One meteorite fell on the ground in Russia, last week. In different circumstances, it could have orbited the earth, or perhaps pass close to the earth and then disappear into the space. It seems that ...
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474 views

Is the speed of sound almost as high as the speed of light in neutron stars?

Have you ever wondered about the elastic properties of neutron stars? Such stars, being immensely dense, in which neutrons are bound together by the strong nuclear force on top of the strong gravity ...
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2answers
92 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 ...
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134 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 ?
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1answer
204 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
256 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 ...
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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 ...
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2answers
201 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 ...
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128 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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248 views

Stellar winds from neutron stars

It seems that this question has not really been explored in the literature. Do isolated neutron stars (which do not accrete material) emit stellar wind? If yes, what composition would it have? If yes, ...
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75 views

What is the furthest object from which fermion rays were detected?

What is the furthest object from which non-electromagnetic cosmic rays were detected?
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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 ...
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93 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 ...
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3answers
250 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 ...
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2answers
433 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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60 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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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
62 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. ...
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4answers
407 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 ...
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74 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, ...
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1answer
283 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 ...
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5answers
3k 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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31 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 ...
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2answers
541 views

Do black holes have infinite areas and volumes?

How to calculate the area / volume of a black hole? Is there a corresponding mathematical function such as rotating $1/x$ around the $x$-axis or likewise to find the volume?
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1answer
95 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
351 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
738 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?
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1answer
651 views

What size will the Sun become once it is a red giant?

How big will the Sun be once it becomes a red giant? How much of the solar system will it engulf?
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5answers
418 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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2answers
950 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
4k 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
104 views

If the observable universe keeps expanding would we eventualy see light 24/7… clouds permiting? [duplicate]

If we can see more observable universe could there be a time when day and night looked the same?
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116 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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69 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
102 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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2answers
188 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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3answers
962 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 ...