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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 to proof that invisiable metter is not simply function from (visiable mass, time) pair?

How to proof that invisiable metter (Dark Matter, Dark Energy) is not simply function from (visiable metter, universe age) pair in terms of known laws of phisics?
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Can a star visually look like a black hole? [duplicate]

Amateur question incoming so please bear with me. Assumptions If a black hole is born from a star going supernova, intuitively it should have the same or less mass compared to the star. Black holes ...
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What is gravity shearing in molecular cloud rotation?

I have read that molecular clouds rotate due to gravitational shearing. What is this phenomenon?
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The Cosmic Microwave Background Paradox

I was reading an article on Olber's Paradox (why the universe isn't as bright as the sun) and the more I read on it, the more the same question came to mind... We know the observable universe is ...
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If one were to distribute the earth into a sheet 1mm thick, how many square kilometers would it cover? [on hold]

I'm just curious. I can't seem to find any information from Google, but I may be looking it up wrong. My theory is that it would cover quite a bit, I'm just unsure of how much.
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Why is the Sun approximated as a black body at ~ 5800 K?

Apparently spectral solar radiation is approximated by a black body at 5800 K. The spectral black body distribution (Planck distribution) is shown below (from Incropera, Fundamentals of Heat and Mass ...
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Pulsar distance estimation

This is quite an interesting problem in astrophysics so I thought it would be a good idea to ask here so we can archive the solution for future reference. Consider a pulsar that emits pulses of ...
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1answer
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Could light and heat reflecting off of surface ice on Earth have a noticeable impact on the sun?

If so, what could be the impact of these reflections on the sun during an ice age on Earth?
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1answer
32 views

Luminosity of a white dwarf

I have a very simple question, yet i am confused.Can someone tell me why in an H-R diagram the white dwarfs are at the bottom left? As in I understand that they would have a high temperature when they ...
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Why is there so much iron?

We all know where iron comes from. However, as I am reading up on supernovas, I started to wonder why there is as much iron as there is in the universe. Neither brown dwarfs nor white dwarfs deposit ...
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2answers
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Finding the distance to a distant star using standard candles

The thing is that i understand how we can measure the luminosity of a close star through absolute and apparent magnitude, because we can easily find the distance through trigonometric parallax. What i ...
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What percentage of stars are giants/subgiants/main sequence etc

I am trying to find the percentage of main-sequence stars along with red-dwarf percentage for my research paper. I did find one article regarding, however it is very old and i require recent data ...
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1answer
109 views

Where is nuclear fusion occuring in the Sun?

My understanding is that the sun is basically a sphere of hydrogen with a helium core, and that the hydrogen is undergoing nuclear fusion to produce helium. There are many images and cross-sectional ...
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Long-term fate of hydrogen atoms in a rogue planet

Imagine a rogue planet drifting in intergalactic space. For the sake of specificity, suppose that it is the size of Jupiter and composed of pure hydrogen. What will happen to it over the next $10^{...
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3answers
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Radius of the Sun

Is it possible to calculate the radius of the sun with minimal amount of physics? I couldn’t find resources on the internet that gives me an answer using a theoretical formula. You are given values ...
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2answers
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Neutron Degeneracy Pressure Calculations

Today I was having a discussion with a colleague about what would happen if you took a 1 cm cube of neutron star matter and set it on the earth. He thought it would fall through and I was trying to ...
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2answers
62 views

What is the reason for the emission of electromagnetic waves from the sun? [duplicate]

What is the reason for the emission of electromagnetic waves from the sun and why curve its in about the visible light is maximum?
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1answer
37 views

Redshift z values and galactic age

Redshift for astronomical objects is often discussed in terms of z-value which I understand to be $\dfrac{\lambda_{obsv} - \lambda_{emit}}{\lambda_{emit}}$, where $\lambda$ is the wavelength. Is this ...
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1answer
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Did Supernova 2007bi really explode due to antimatter creation?

I was watching a video (https://www.youtube.com/watch?v=IZ59_akUUBs) about massive explosions and came across 2007bi. The video stated that this SN happened due to gamma-ray driven antimatter ...
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1answer
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At what velocity will the moon be able to escape the earth's orbit?

I haven't found an answer to this question online so correct me if I am wrong. This is the escape velocity equation: $v_{esc} = \sqrt{\frac{2GM}{r}}$ and by plugging the known values, this is the ...
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1answer
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Electron density Saha Ionization Equation

Saha-Boltzmann equation describes the ratio of number densities between any two consecutive ionization states and its product with the number electron density i.e. $$n_e\frac{n_{i+1}}{n_{i}}$$ Here, ...
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2answers
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Can time dilation show who's moving?

Imagine a person going in a spacecraft moving away from the Earth, when he return from his journey he notice the time has passed slowly than for the habitants on the Earth. Noting this, we can ...
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1answer
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How many times do solar protons repeatedly fuse and fission before they form deuteron

In the proton-proton chain reaction in the Sun, the first step is $$p + p \rightarrow \; ^2_2{\rm He} .$$ After this, the most likely thing to happen next is that the reverse reaction occurs: the $^...
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1answer
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How the cosmic inflation solves the horizon problem (an exact solution)?

I am reading an article, Inflation and CMBR by Charles H. Lineweaver. https://www.mso.anu.edu.au/~charley/papers/canberra.pdf (Page 5/13) He explains the inflation period as the shrinking of the ...
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1answer
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Temperatures of Galaxy Clusters

Recently I've read about clusters of galaxies and have tried to understand how one can measure their mass and temperatures. Clearly, we can physically measure a couple of things such as the flux of X-...
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2answers
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Is there an equation for the amount of energy from a collapsing star BEFORE it creates a black hole?

(I could be phrasing my question incorrectly, so bear with me as I try to explain it.) Recently I've been very interested in the geometry and physics of black holes, so I started messing around with ...
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Does Hawking Radiation Violate General Relativity? [duplicate]

“Electromagnetic radiation which, according to theory, should be emitted by a black hole. The radiation is due to the black hole capturing one of a particle-antiparticle pair created spontaneously ...
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1answer
121 views

Could the singularity of a black hole just be an iron / dark matter sphere? [duplicate]

A singularity would break physics wouldn't it? How does a massive star collapse and suddenly fall into a point in space with no dimensions what so ever when it had a core and perfect balance between ...
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The basics of neutrino telescopes

I'm trying to understand the basic operation of the ANTARES neutrino telescope. Here is what I've gathered: The detection of neutrinos relies upon the detection of muons. Cosmic rays and neutrinos ...
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3answers
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Mass of potential gravity energy?

Assume a system where there only two 1 kg solid iron balls floating in space. The two balls are touching each other, so the potential gravitational energy between them is 0. Now I move them 1000 m ...
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1answer
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What is the closest distance for an undiscovered old neutron star and how long would it take to get here? To help people scared of neutron stars

This is to help people who are scared of neutron stars. My questions are What is the faintest a neutron star could be How close could it be and not yet be detected How long would it take to get here ...
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1answer
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Jones representation of Unpolarized light

What is the Jones matrix representation of completely unpolarized light? Context : Majority of astrophysical sources' emission is totally unpolarized or partially polarized. I need to know the ...
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1answer
32 views

Length dimension in the Lane-Emden equation

I was deriving the Lane-Emden equation from the hydrostatic equation and the polytrope. I was following the procedure presented by Carroll & Ostlie's book. I was stuck on this part, it said that ...
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1answer
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Moving singularities

I am aware that black holes can move through space-time. Is there a way to move a naked gravitational singularity artificially? Sorry if this is a little stupid, trying to figure out the feasibility ...
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What is angle between ray to center of the sun and its perimeter?

If I took a ray from a point on the earth P to the center of the sun. And another ray from the same point on the earth to the perimeter of the sun. What would the ...
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2answers
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Do only 'giant stars' fuse large amounts of elements other than hydrogen and helium?

Do only giant stars initiate 'full-on' carbon (and higher element) fusion, even though red giants on the larger end of the spectrum create carbon and oxygen via producing helium per the CNO cycle?
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Why does a star die once it has iron?

I found out that iron is the death element for stars, but I couldn't find why can anyone knowledgeable on stars explain why iron causes the star to die?
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1answer
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Why does a tidal bulge result in a net torque on the Moon?

I understand that a tidal bulge is caused because the side of the earth facing the moon experiences a stronger gravitational force than the other. This results in the oceans on that side slightly ...
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3answers
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Do supernovae push neighboring stars outward?

I know that a supernova can mess up the heliosphere of nearby stars, but I'm wondering if it could physically push neighboring stars off their trajectories. It's fun to imagine all the stars ...
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1answer
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What is the least energy trajectory in Astronomy?

Hi I wanted to know what the least energy trajectory is in relation to astronomy as I can't seem to find a good answer on Google. I want to know because I am trying to answer this question: A ...
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How to calculate the corotation radius?

I am studying this paper: P.Ghosh & F.K.Lamb, APJ, 232, pag.259 (1979) I do not understand how the authors calculate the corotation radius, $r_{co}$, where the matter of the disk has the same ...
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How is black hole formed after a supernova explosion?

Does all the mass of a core collapsing star get scattered during a supernova explosion? If it does, then how can a black hole be formed without any remaining mass? Or are there remnants of the star ...
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1answer
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Doubts about the formation of the bullet cluster

The bullet cluster is formed by the collision of two clusters of galaxies. After the collision, the stars and galaxies in those two clusters passed through each other. But the intergalactic gas clouds ...
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1answer
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Spacetime drag and galaxies' radial velocity mismatch

We know - or theorize - that a spinning black hole drags spacetime in its surroundings, producing measurable effects on the accretion disk (the minimum stable orbit radius). What I cannot grasp is why ...
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1answer
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If we know the distance of a distant light emitting object, how could we know the age without knowing how long the light has been here?

I have been contemplating the age of our observable universe and I was unsure as to how we could tell the age by only divdeing the distance by the constent with out knowing how long the light has been ...
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1answer
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How is the energy density of radiation relatedd to the energy density of particles and the critical density?

In a solution set I was reading for cosmology I saw that the energy density of radiation is defined as $\epsilon_r=\epsilon_c-\epsilon_p$. Where $\epsilon_p$ is the energy density of particles at ...
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1answer
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number density of photons

My lecturer put up as a solution to the number density of photons to be $n_{o\gamma}=\tfrac{8\pi}{c^3}\int^{\infty}_0(\tfrac{kT}{h})^3\tfrac{x^2dx}{e^x-1}$. The integral on the right hand side being ...
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1answer
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How is the co-moving co-ordinate defined mathematically in cosmology?

The relationship between proper distance and co-moving distance in cosmology is given by: $$R(t)=a(t)r$$ Where $R(t)=$ the proper distance which corresponds to where a distant object would be at a ...
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1answer
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Unmagnetized plasmas in space

Please, I need some information about high temperature plasmas in astrophysical environments. To my knowledge, plasmas in astrophysical environments are magnetized (is it true?). Are there ...
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Where are the high mass White Dwarfs that are going to create type 1a SN

The mass distribution of WD stars is explained at Why is the white-dwarf mass distribution highly peaked?. However this mass distribution shows very few stars that are about to exceed the WD limit of ...