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Questions tagged [astrophysics]

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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Could dark matter be radiation pressure?

I watched Stephen Wolfram on a podcast explaining this idea last night. He said that dark matter could be explained as "spacetime heat". My contention is that stars and black holes trap a ...
Eschaton Magazine's user avatar
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Question about the toroidal magnetic field in quasars and the role of an ergosphere

1) Introduction Most of astrophysical bodies (in this context: formed stars, young stellar objects and black holes) produce or are immersed in a non-zero magnetic field $\vec{B}$. It is common, since ...
M.N.Raia's user avatar
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What is the energy density of gravitational fields around neutron stars? [closed]

The field strength of gravitational fields around neutron stars is extremely high. This would lead to an extreme negative value for the energy density. But if an absolute negative energy density is ...
Wolfgang Konle's user avatar
6 votes
2 answers
118 views

Why Cepheids have Period Luminosity relation?

According to my astronomy teacher, Cepheids is a type of variable stars that has Luminosity-Period relationship: $M \propto log(T)$ , where $T$ is the pulsation period of Cepheids. But I have a ...
Polaris5744's user avatar
6 votes
6 answers
3k views

Why is pressure in the outermost layer of a star lower than at its center?

I have done the math and I have obtained the hydrostatic pressure in a star is lower at the outermost layer of a star than in its center, where the pressure is actually maximum. Although the equations ...
Lagrangiano's user avatar
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Does Kirchhoff's law of thermal radiation fail for optically thin sources?

A box made of any material with a small hole in it will give blackbody radiation. According to my textbook by ARNAB RAI CHOUDHURI, If you place an optically thick source of same temperature as the box ...
Adithya Bharath's user avatar
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1 answer
25 views

What is emission line ratio?

As the header stated, what exactly is the 'emission line ratio'? Like, [O III]/Hβ or [Ne V]/[Ne II]. Recently I've been reading some research papers in astronomy and astrophysics pertaining to ...
ZenithalizeSquads's user avatar
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5 answers
75 views

Is the radiation from closed boxes blackbody radiation irrespective of the material of the box?

Suppose I have a box made of silver at temperature T, in thermal equilibrium with the surroundings. Silver has very low absorptivity and hence it will have the same low emissivity to maintain thermal ...
Adithya Bharath's user avatar
3 votes
2 answers
667 views

When do we talk about spaghettification or pancakification in black holes?

So I've been doing some research for a while now, and yesterday came across the video of PBS space time talking about what happens to quantum information in a black hole. In the thought experiment ...
Anais-Ellie Gucek's user avatar
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What is the difference between the virial radius, the total mass-energy density radius and the critical density radius for a galaxy?

For a regular spiral galaxy like the Milky Way, how are these concepts different from each other?
Saminul Haque's user avatar
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Should luminosity distance be $0$ at $z=0$?

I am working on coding up the luminosity function for blazars but I have ran into a problem. In equations 1-3 of this paper https://arxiv.org/abs/1912.01622 they state that the flux can be broken down ...
John's user avatar
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Realistic black holes

If I understand the answers provided in this Link Why singularity in a black hole, and not just "very dense"? Then the singularity at $r=0$ may just be a mathematical artifact, and may not ...
Precious Adegbite's user avatar
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Why are planets denser as you approach the center?

Gauss' law says that the net electric force inside a hollow, uniform, not rotating sphere is zero. Since gravity is also proportional to the inverse square of the distance, I assume this should apply ...
Joseph Hirsch's user avatar
1 vote
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Mass-volume relation for a star - explanation

In the game Universe Sandbox, I created a gas giant (made of pure hydrogen) and begun increasing its mass and watched how its radius changed and how it evolved into a star. While it was already a ...
Henry05's user avatar
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The magnetic force between the earth and the sun

There is a magnetic field around the earth and a stronger one around the sun. I guess there should be a magnetic force between the sun and earth. Now, shouldn't we take the magnetic force into account ...
Future Math's user avatar
2 votes
1 answer
63 views

What is the function that demonstrates a planetary transit light curve given a planet's projected distance from its star?

Last night I was measuring the brightness of a Hot-Jupiter parent star to try and isolate the transit light curve (specifically Tres-2b). I have been wondering how to obtain the function that ...
Kareem Shamma's user avatar
2 votes
1 answer
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Can glueballs and bosons survive indefinetely in space (forming structures)?

I have been recently interested in looking for possible structures (ranging from clumped structures like "stars" to diffuse clouds of gas or halos) made from standard model-particles other ...
vengaq's user avatar
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Using Gravitational Waves as an observation technique

In theory, could you possibly use Gravitational Waves as a way to detect and observe subatomic particles without disrupting them if the gravitational wave was small enough? And then translate that ...
Jacob B's user avatar
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2 answers
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Relationship between gravitational force and fusion energy in stars [duplicate]

From what I understand, stars like our Sun constantly have a gravitational force on their surface due to their mass, which is balanced out by the fusion reactions taking place in the core of the Sun. ...
Waev's user avatar
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1 answer
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Are pure quark stars possible?

Has it been established that structures formed from quarks (like quark stars: https://en.wikipedia.org/wiki/Quark_star) are possible in principle ? I have read about the possibility that inside ...
vengaq's user avatar
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0 votes
1 answer
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Using helioseismology what are the equations astrophysicists use to determine the age of the Sun? [closed]

Astrophysicists talk about solar models when determining parameters of the Sun. But these models must be built from equations. When explaining to the general public what these equations are would be ...
Walter 's user avatar
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1 answer
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Strength of a phase-transition

I'm currently studying neutron stars for a summer research project, and it uses the terms 'weak' and 'strong' transition for nuclear matter in its literature. Can someone explain (in terms that a ...
physicsnoob's user avatar
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0 answers
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Can there be structures made from neutrinos that can have angular momentum?

Would it be possible to eventually have structures made from neutrinos somewhere in the universe, as it is indicated in this question (Are neutrino stars theoretically possible?), like halos of ...
vengaq's user avatar
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3 votes
1 answer
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Does the Kardashev Scale have any practical application?

As the question states: are there any practical applications of the Kardashev Scale?
Dancrumb's user avatar
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Can ring singularities form a Hopf link?

Can ring singularities form a Hopf link?
Michael's user avatar
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Inconsistency in numerical and slow-roll solutions of Mukhanov-Sasaki equation during Inflation

from my lectures in cosmological inflation, we derived the Mukhanov-Sasaki equation and its initial condition (Bunch-Davies). From here, it was of our interest to find a numerical solution of the ...
Jules Alvarez's user avatar
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1 answer
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Mass formation of a neutron star Vs White dwarf

I have been researching the different outcomes of a star's death. I understand that the main factor is the star's mass at the end of its life, along with others such as its metallicity. Well, the ...
Gorga's user avatar
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1 answer
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How would an observer view the apparent motion of planets in the Neo-Tychonain model?

When observing the motion of bodies in the solar system, the common observer viewpoint is that situated on Earth. However, when viewing the apparent motion of Earth from Mars in a given system, for ...
phy_theo's user avatar
11 votes
1 answer
550 views

Does the formation of a neutron star always require a supernova explosion?

Is a supernova explosion an essential condition for the formation of a neutron stars?
A K S's user avatar
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1 answer
33 views

Sudden drop in temperature in Sun convective zone

In the solar temperature graph, why does the temperature drop suddenly in the convective zone? Is it because some energy is needed for ionisation?
yolopoi's user avatar
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1 answer
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The Maximum Size of a Theoretical Dyson Sphere

In the paper "Dyson spheres around white dwarfs" (https://arxiv.org/abs/1503.04376) it clearly states on page 11 that the bonds required for making such an object are in the order of $\...
Recramorcen's user avatar
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1 answer
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Minimum size for a planet to have a molten core

What would be the minimum size for a planet or moon so that it would have a molten core? Gravity and density would play a part but how could this be worked out?
Michael Mcgarry's user avatar
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Magnetic tubes or magnetic field lines around a black hole?

A picture is worth thousand words: Magnetic field lines, unlike magnetic tubes, have a continuous distribution. Recent pictures of black hole magnetic structure show tubes. Is there a model that ...
Shaktyai's user avatar
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4 votes
1 answer
139 views

Supressing proton and neutron decay?

I was wondering whether the decay of neutrons and protons (if they happen to be able to decay, as it is predicted by some GUTs) could be avoided in some cases. Let's begin with neutrons: In principle ...
vengaq's user avatar
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1 vote
0 answers
104 views

Can black holes exchange Hawking radiation, avoiding complete evaporation?

I was wondering if it would be possible that, as a black hole radiates its mass as Hawking radiation, another black hole could absorb that radiation and then when the second black hole radiates its ...
vengaq's user avatar
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1 vote
0 answers
28 views

Galaxy harassment; flyby encounter (tidal interaction)

This following image is from the paper https://adsabs.harvard.edu/pdf/1978AJ.....83..219R#page=4 It shows the path of a flyby encounter of NGC 3627 (M66) with the galaxy NGC 3628 (the Hamburger galaxy)...
Hey's user avatar
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1 vote
1 answer
63 views

Obtaining TOV equations

I am trying to obtain the first TOV equation $$ (\rho+p) \frac{\mathrm{d} \Phi}{\mathrm{d} r}=-\frac{d p}{\mathrm{~d} r} $$ using the metric $$ \mathrm{d} s^2=-\mathrm{e}^{2 \Phi} \mathrm{d} t^2+\...
Gorga's user avatar
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1 vote
1 answer
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Can super heavy elements form inside black holes?

I have read that heavy elements like gold and uranium are formed due to extreme pressure, through a process similar to nuclear fission. I wonder if something like atomic no. 500 or 5000 could form ...
Gopal Kaushik's user avatar
1 vote
1 answer
30 views

If a star's luminosity doubles, does its received flux double?

If the luminosity of a star increases or decreases in some way, would the received flux increase or decrease by the same amount (linearly) or would it change by the square of the luminosity (inverse ...
Astrovis's user avatar
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1 vote
0 answers
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Is there a way to calculate the habitable zone distances of a star?

What would you need to calculate the habitable zone distances of a star? I am aware of the Stefan-Boltzmann Law and Wein's Law to calculate the Luminosity of the star, and that the flux decreases with ...
Astrovis's user avatar
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1 vote
2 answers
40 views

Angular velocity vs Angular frequency

Are these two omega same? (angular frequency of a current oscillating loop and angular velocity of a rotating body)
Shreyansh Kabir's user avatar
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0 answers
31 views

Is the sun multinucleated or is there just one point at or near the center of the sun where fusion is occurring?

I was just reflecting upon my thinking and probably any illustration in books or movies: I assumed a single general area near the "geographical" center where the actual fusion occurs. But ...
releseabe's user avatar
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0 votes
2 answers
51 views

Could another star render color better than the Sun? If so, would a human be able to tell?

Disclaimer: This might be a better question for Worldbuilding SE, not completely sure. I read today that the standard method of measuring color rendering index (CRI) is based on natural light (e.g. ...
Faustawk's user avatar
4 votes
1 answer
383 views

What are the odds of a rogue planet that enters into a galaxy reaching the black hole at the center of the galaxy?

I am wondering if anybody has ever calculated the odds of a rogue planet, which has been traveling through interstellar space and then enters into a galaxy, being able to travel all the way to the ...
user57467's user avatar
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0 answers
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Turnaround radius being increased in fast collapsing regions?

In the context of formation of large-scale structures, there would be a turnaround radius where expanding matter would detach from the Hubble flow and start to collapse (https://www.aanda.org/articles/...
vengaq's user avatar
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2 votes
1 answer
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What is the energy density on the surface of a polytropic gas sphere?

If one solves Einstein's field equations for the metric of polytropic gas sphere, one stets the gas density at the surface to zero. However, such condition describes vacuum where both pressure and ...
JanG's user avatar
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1 answer
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Where does the energy density of black holes fit in a figure with the different energy densities of the universe like matter and radiation? [closed]

Based on the black hole mass, giving that lower mass black holes have higher mass densities than higher mass black holes. Energy Densities `The density is dependent only upon the mass of the black ...
New's user avatar
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8 votes
1 answer
2k views

Is this an actual photo of frame dragging?

Is this new image (below) of polarized light surrounding Sagittarius A, showing actual frame dragging being captured by the magnetic field? The image is from this article If not, how would a photo ...
foolishmuse's user avatar
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0 votes
0 answers
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A general theory of convection currents using continuity equations

In an Astrophysics & Cosmology summer programme I attended last summer at UCL we were taught that stars seem to transport matter from the regions near the core to the surface through convective ...
Lagrangiano's user avatar
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1 vote
0 answers
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How close does a dwarf star have to be to remove the corona from its neighbour in an elliptic binary system?

It is possible for a larger (wider, but less massive) star to mutually orbit a heavy dwarf companion star in a binary system. If the dwarf star gets close enough it can attract the corona of the ...
spraff's user avatar
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