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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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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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1answer
360 views

What is the difference between granulation and supergranulation in the Sun's photosphere?

Granulation and super granulation seem to be some sort confused topics as they are due to the heated particles coming out of the surface. What is the difference between the two?
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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 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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1answer
49 views

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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58 views

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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How is it that some nebulae are rotating and others are not?

First, I should make it clear that this isn't a question about angular momentum (unless I may have completely missed something). It is my understanding that a nebula must have some inherent initial ...
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Metal-rich star formation

While discussing star formation on cosmological scales with some classmates, we mentioned the breakdown between the different stellar populations via metallicity: Population III: $Z = [{\rm Fe/H}] \...
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1answer
139 views

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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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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187 views

What is the average temperature of mass in the universe?

That is, ignoring speculative concepts like Dark Matter and just summing across stars and gas clouds etc
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187 views

How does Planet 9's perihelion and aphelion affect the Kuiper belt objects?

Assuming that the existence of Planet 9 is confirmed and it really exists, how does it affect the orbits of the Kuiper belt objects? My understanding is that the discovery came in part from the ...
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1answer
132 views

How to get the Chandrasekhar Limit from a plot?

at the moment I am trying to understand, how to obtain the Chandrasekhar mass limit from a plot like shown above. Because for $n$ = 3, the mass is independent of the radius of the white dwarf. But in ...
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When galaxies collide, what happens to dark vs. light matter?

I have read that galactic collisions have been used as evidence demonstrating the effects of dark matter. In particular, that luminous matter slows down and interacts while dark matter shoots through, ...
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2answers
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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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2answers
92 views

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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2answers
231 views

Blackbody flux model (Xspec: bbodyrad)

Above is the model I fit my data too in Xspec. Xspec is a piece of software where you can model spectra from observations with their set models. It handles things like absorption, reddening, etc. to ...
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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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1answer
223 views

How much of the Solar convection zone is completely ionized?

I was reading about the energy transportation in stars here, and I found this: "The outer portion of solar mass stars is cool enough that hydrogen is neutral and thus opaque to ultraviolet photons, so ...
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1answer
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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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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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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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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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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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2answers
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How do we know that these radio bursts are from billions of light-years away?

NASA just announced that they detected the first radio bursts from outside of our galaxy. Astronomers, including a team member from NASA's Jet Propulsion Laboratory in Pasadena, Calif., have ...
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2answers
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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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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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2answers
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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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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 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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What does Carlo Rovelli mean by “blurring”?

In Rovelli's book The Order of Time, he often refers to blurring. Can you help me to understand what he means? He says we observe the universe from within it, interacting with a minuscule portion ...
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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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237 views

How do fluids behave in space?

In outer space under absence of any external force (like gravity) can a free liquid develop pressure due to cohesive forces? Will the liquid be in spherical shape and will pressure increase towards ...
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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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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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1answer
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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 isn't dark matter just ordinary matter?

There's more gravitational force in our galaxy (and others) than can be explained by counting stars made of ordinary matter. So why not lots of dark planetary systems (i.e., without stars) made of ...
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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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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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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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4answers
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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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1answer
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Does the number density of photons $n_\gamma\approx 10^8 \:\mathrm m^{-3}$ refer to CMB photons only?

When we talk about the present-day number density of photons ($n_\gamma\approx 10^8 \:\mathrm m^{-3}$) in the universe do we mean the number density of CMB photons? I mean there are other sources of ...
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Could Gamma ray bursts be caused by matter-antimatter annihilation?

As far as I know a collisions of matter and antimatter leads to the complete annihilation of both, whereby 100% of the rest mass of the particles is converted into gamma rays. Could this mechanism be ...