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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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Does this method that I've thought of for calculating the width of the umbra in a total solar eclipse work out?

Hello I wanted to calculate the width of the umbra of the shadow of the moon that is projected onto the earth during a total solar eclipse, based on the distance that the moon is from the earth. This ...
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How can I deduce a probability using a Kroupa IMF and a set of observed stars along a model isochrone?

I’m plotting a colour magnitude diagram for an open cluster and setting it against a few model isochrones. I want to deduce the probability that the cluster belongs to one or the other isochrone, but ...
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Intermediate product of CNO cycle

CNO cycle of stellar nucleosynthesis involves several steps in which different isotopes of Carbon, Nitrogen, and Oxygen are transmuted into each other when hit by a ...
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How can a gas be in circular orbit when centrifugal force is dominant in an accretion disk around a black hole?

In the textbook "Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects" by Shapiro and Teukolsky, the author makes the following statement while discussing the standard thin disk ...
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How can a non-rotating black hole or singularity be created?

Every star or other massive body in the universe rotates, if only a little. If such a body collapses, its spin, any spin at all, and thus, angular momentum approach infinity as r approaches 0. Angular ...
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Texts on Hoag's Object

Are there any good texts online that someone can recommend on Hoag's Object? It is a very weird galaxy and I would like to learn more.
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Several disscussions and questions made on black holes [duplicate]

This isn't a duplicate question, this is revisting the whole black hole model: If an object with mass M is compressed to radius r, where r ∈ (0,Rs] such that Rs is the Schwarzschild's radius of the ...
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How can Sun burn in space?

If there is no oxygen in space how can sun burn in space. (even though I know fire is caused by nuclear reaction inside sun)
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Do solar energetic particles follow the Parker spiral?

I understand that the solar wind follows the Parker spiral shape of the Sun's magnetic field, thus it is possible for solar wind from a point on the opposite side of the Sun to reach Earth. I have ...
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Which “straight line” should I travel to maximize the number of temperature gradient reversals I experience?

Fire a neutrino from whatever starting point and in whatever direction you like in the universe. As the neutrino travels, it will traverse many temperature gradients in its ambient environment. What ...
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Disk-like structures spectra vs ring spectra?

In the introduction to this paper (https://arxiv.org/abs/1803.06423) it is mentioned that disk-like spectra was observed in black hole X-ray binaries, when models would expected to be unstable (...
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Would the Doppeler effect be incorrect to use as evidence to support an expanding universe?

In our science class we have a question to answer, which is 'explain how redshift supports the idea of an expanding universe'. I am not sure how to answer this question, as I know that there are '...
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Rotating and precessing magnetic dipole

I am considering the problem of a rotating and precessing magnetic dipole (my final aim is to study the effect of the magnetic field on the production of gravitational waves in a binary neutron star ...
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Are wet mergers good for star formation?

In my astrophysics lecture my professor said wet mergers are bad for star formation since it often results in gas being fed to the black hole. In the wiki however it says the opposite. What is the ...
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Why are most of the stars in the central bulge of a galaxy?

Just wanted to know if this is because of gravity initially clumping most of the matter at the centre of the galaxy during its formation or some other reason? It was never really discussed in my ...
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Why do stars start off burning deuterium?

Given hydrogen is a lighter and more abundant element, why do most baby stars start off burning deuterium?
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Is there any time difference when we see distant a object? [duplicate]

I was just wondering that We see objects thru our eyes and light has to reach our eyes so that our brain can process that light. But then there must be a time difference between that object which I ...
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Adiabatic and isothermal astrophysical flows

Astrophysical flows around black holes (like accretion and winds) can be adiabatic as well as isothermal. In adiabatic flows, the flow is non-dissipative except at the shock location. However, in case ...
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Why physical / cosmological models that have been falsified weren't abandoned? [closed]

Before anything, I'd like to say that I'm a layman (non physicist) and english is not my main language; I apologize if my choice of words make me sound rude / arrogant, that is not my intent. I often ...
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Deriving equations for Equatorial -> Galactic transformation via Euler Angles

As the title suggests, I'm looking for a derivation of the transformation equations between the equatorial and galactic coordinate systems via Euler angles. $\cos{b}\cos{(l-l_{0})} = \cos{\delta}\...
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What affects the propagation of secondary cosmic rays?

Primary cosmic rays produce, upon entering the Earth's atmosphere, a whole load of secondary particles. These primary particles are necessarily stable particles such as protons, electrons, and ...
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What is the relationship between the colour of a star and its mass to light ratio

We were talking about methods to measure the mass of a galaxy and one way was to measure the mass to luminosity ratio and multiply by the luminosity. That seems like a trivial equation but apparently ...
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Why is most of the star formation that goes on in the milky way occurring in the spiral arms?

This fact was mentioned by our astrophysics lecturer and I can't seem to understand why. Isn't the densest and hottest part of our galaxy the central bulge? I would've thought star formation would ...
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Can a gas cloud of pure helium collapse and ignite into a star?

Assuming there could be a giant gas cloud with negligible amount of hydrogen and metal (elements with atomic number $Z\geq3$), could it collapse gravitationally and form a pure helium star that would ...
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Was Titan once warmed by a hot Saturn, & therefore much more Earth-like than it is today?

Is it possible that 4 billion years ago, Saturn was sufficiently hot to act as a second sun to Titan, so that conditions on Titan were then similar to those on Earth?
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Explain to me why the following reaction can happen in big stars but not on earth

$$ \rm {}^{12}C +{}^{12}C\rightarrow {}^{20}Ne + {}^4He $$ why doesn't this reaction occur on earth? but occurs in big stars?
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Are / Why are the H II regions positively charged?

One of the questions in our recent astrophysics course homework was to find the general opacity $\kappa$ of H II regions. We know that the H II regions are almost entirely ionized hydrogen and I ...
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Physical reason behind the origin of shock waves in astrophysics [duplicate]

Shock waves arises in astrophysics in accretion flows and in winds. But we know that shock waves usually occurs in supersonic flows when the flow encounters any obstacle or when the properties of the ...
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Why hydrogen lines are less visible in the Sun spectrum than in supernovae clouds?

Supernovae clouds are very colorful, and if I trust documentaries I watched, the colors are due to excitation of elements, as in fireworks. Since the Sun is mostly made of hydrogen, I suppose those ...
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Why is the Sun made of light elements only?

Since the entire solar system inherits its heavy elements from supernovae unrelated to our star, I fail to understand why, while capturing most of said system's matter, the sun only contain light ...
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How is V838 Moncerotis Expanding at 10x the speed of light? (It isn't - but sure looks like it)

The first picture from the Hubble Telescope was on May 20, 2002. A subsequent set of pictures culminating in October 2004 showed that it had expanded at about 1 LY per month. Now as we know there is ...
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Vertical equilibrium condition in thin adiabatic black hole accretion flows

In adiabatic thin accretion accretion flows around black holes, we consider the vertical equilibrium condition where the thickness of the flow is very small as compared to the radial coordinate, i.e., ...
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Do super dense objects smear instead of colliding?

I am watching a video (https://www.youtube.com/watch?v=C1mmTwjHhHs) and it is discussing a pair of neutron stars colliding and how the LIGO detected them. In this video and other videos on such ...
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Query about using HR diagram to determine stars progression through its main sequence

There was a problem in my astrophysics lecture which showed a cluster of stars (M92), the apparent magnitude was plot against the B-V colour for each star in the cluster: Along with other graphs, we ...
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Understanding the notion of lose or win of angular momentum in accretion disk

Here is below a slide of one of my lecture in planetology : I understand well the fact that ring A will be slow down by friction with ring B since ring B is rotating slower and the inverse process (...
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Interpretation of critical points (or sonic points) in fluid flows

In the study of transonic flows in astrophysics, we come across critical points (also known as sonic points) where the fluid velocity equals the velocity of sound. Across such critical points, a ...
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CNO-cycle in Population III stars [duplicate]

It has been stated several times here and probably elsewhere that the first population III stars were unable to undergo H-to-He fusion via the CNO cycle as there was virtually no carbon-12 at the ...
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How does a Thorne Zytkow star die?

A Thorne-Zytkow star is one where a red giant or supergiant contains a neutron star at its core, formed from the collision of the giant with the neutron star. It is believed that one has been found in ...
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How long would it take for Earth to become desolate after being slung from orbit?

I rather enjoy watching some of the what if scenarios on YouTube, and today I had one trigger my urge to seek out some knowledge on a curiosity I have. A lot of media out there explains that the ...
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Importance of speed of sound in astrophysical flows

The speed of sound is very important in astrophysics in the study of accretion and wind flows. I have two questions as follows: What is special about the speed of sound and not any other value of ...
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A book about extragalactic astrophysics?

I'm an undergraduate student, writing my thesis. And I look for an advanced book of extragalactic astrophysics that contains information about Line Emission Galaxies. I already read "Extragalactic ...
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Doubt about the Einstein Field Equations (EFE) of a Magnetar

The Schwarzschild solution could be an good model for a planet and a star, without rotation and electric and magnetic charge. Besides the fact that this solution is spherically symmetric. The metric ...
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Do we really need a new physics? [closed]

I have heard many times in news that a new discovery has taken place, and we need a new physics. It has recently been announced in scientific news that the world is apparently expanding faster. And ...
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Moving moon explanation

I saw the moon moving in a fast pace several times with the naked eye, even during day time when its cloudy. How is that possible? I asked my teacher about it and he said its just an illusion, but ...
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Is a galaxy made up of dark matter really a galaxy?

So I am watching a video discuss Dragonfly 44. The galaxy is made up almost entirely of dark matter and is 100x dimmer than the Milky Way galaxy. Wouldn't this mean it is just a large clump of ...
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Why are more massive white dwarfs smaller?

I understand that a white dwarf is supported by the Pauli Exclusion Principle and that the larger the gravitational force against them, the closer the electrons must pack. But I have two queries: ...
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Query about the evolution of the sun, from hydrogen shell burning to helium flashpoint

My understanding of the transition from hydrogen shell burning to helium flash point: The hydrogen shell burning occurs because the hydrogen in the suns core during the main sequence has been used up,...
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What imparts the linear motion or the tangential velocity to natural satellites like the moon to enable them to be in orbit around the earth?

From Newton's laws of motion & gravitation, it is clear that the force of gravitation provides the necessary centripetal force which acts along the line joining the centre of masses of the earth &...
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Strange quarks in neutron stars

Recently I have read that the pressure within neutron stars can be so extreme that it can cause the deconfinement of quarks to form a kind of quark 'soup' and that these extreme conditions allow for ...
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How much in the past are we viewing the accretion disk of a black hole?

Sine the gravity near a black hole is so high, the time moves slower than the observer(in our case we from the earth).In that case, imagine if are viewing a black hole's accretion disk(the innermost ...