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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Computation of error on $C_\ell$ with fraction of sky $f_{\text{sky}}$ and $\Delta\ell$

I try to demonstrate the expression of error on a $C_{\ell}$. Below the expression of standard deviation on a $C_{\ell}$ that I would like to get: $$\sigma_{C_{\ell}}=\sqrt{\dfrac{2}{(2 \ell+1) f_{\...
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Fetter and Walecka - Quantum Theory of Many-Particles - Problem 2.8 [closed]

As a model of a white-dwarf star, consider an electrically neutral gas composed of fully ionized He ($\alpha$ particles) and degenerate electrons. (a) Write the equation of local hydrostatic ...
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What's the minimum possible size of a round astronomical body?

What's the minimum possible size of a spherical shaped rocky planet or satellite? Is it possible to occur a spherical shaped planet without having a molten core?
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What is the pressure that dark energy exerts on stars and planets while increasing the distance between them?

What is the pressure that dark energy exerts on stars and planets while increasing the distance between them? I can understand that the pressure should be at a volume scales lower than molecules ...
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Why are wide binary systems assumed to contain negligible dark matter?

I'm doing a project that simulates wide binaries to do gravity tests, specifically a dark matter vs MOND test. I've come across similar papers, and their justification for using wide binaries for this ...
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May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again?

May a star explosion be in that way weak that the expelled material gradually recollapse and form the star again? My question is not about would that explosion leave a neutron star as a remnant but ...
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How does the density of main sequence star impact spectral lines and the depth/width of a spectral line graph?

My understanding is that a denser star will cause the width of a spectral line to broaden and it will cause the depth of the intensity plot to increase (dip lower). Would this be correct? Also, is ...
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Graph Interpretation of Gravitational Waves

In the image is the data recorded by the LIGO's 2 observatories in USA. What is its interpretation? I mean what does the zig zag lines represent? Similarly, what does the blond red and blue lines (...
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Relation between Matter Power spectrum $P(k)$ and Matter Angular power spectrum $C_{\ell}$

Summary: $\quad$ I would like to go deeper in the relationship between Matter power spectrum and Angular power spectrum. From a previous post about the Relationship between the angular and 3D power ...
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What is the heaviest element being produced in Sun?

Helium is being produced currently in Sun. 3 questions. Other than Helium what other elements are currently being produced in Sun right now.? Looks like in 5 billion years, when Sun will become a ...
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Why does relativity affect relativistic jets?

Relativistic jets are regions outside black holes where matter is spewed out. Wikipedia states that these jets will demonstrate relativistic effect such as relativistic beaming. I don't understand why ...
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Compute the variance of spectroscopic Shot Noise in cosmology context

I would like to know the right expression for the expression of variance of Shot noise in spectroscopic probe. Sometimes, I saw $$\sigma_{SN,sp}^{2} = 1/n_{sp}$$ with $n_{sp}$ the average density of ...
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Four Momentum in an Isotropic and Homogeneous Universe

We define the four-momentum of a particle by $p^\mu = (E, \mathbf{p})$, where $E$ is energy and $\mathbf{p}$ the three momentum of the particle. In cosmology, we conventionally use the Friedmann-...
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Interaction of supersonic wind with static Inter-Stellar Medium (ISM)

Recently I was studying about the interaction of supersonic flow (wind) with a slowly flowing medium. In a paper by Dyson, Falle, and Perry 1980 MNRAS stated that when a supersonic wind impinged upon ...
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Are the physical structures in our sun of comparable complexity to those in the human brain? [closed]

The writings of Rupert Sheldrake tend to provoke strong emotions, be they ridicule, curiosity, outrage, sympathy, disgust, or otherwise. While Physics SE is not an appropriate forum in which either to ...
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Cosmological models of the expansion of the universe for different curvatures

My question refers to page 38 of Tong's Notes on Cosmology. Here we consider a matter dominated universe and derive the equation $$2h^\prime + h^2 + k = 0$$ for $h = a^\prime/a$, where $^\prime$ ...
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Change in the mass of a star due to nuclear fussion of Hydrogen [closed]

Let's suppose a star is initially composed only of hydrogen. After a certain time $t$, it has consumed the $5\%$ of its initial hydrogen, fusing it to produce helium, according to the following ...
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In plasma physics what does beam of particles mean

I often hear about a beam of particles on top of a background population in plasma physics. What does exactly beam mean? Is it a subset of particles that belong to a different distribution? What ...
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Relation between central and mean density in a White Dwarf (polytropic model)

I'm currently studying the radius of a white dwarf and, in deriving some useful equations, I've seen my professor use the following relation: $\bar\rho=\frac{\rho_c}{6}$ when using a polytropic model $...
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Perturbation theory on perihelion advance

I'm trying to get a relativistic solution to Kepler's equation starting with $$\frac{d^2 u}{d\phi^2}+u = \frac{M}{L^2}+3Mu^2$$ by ignoring the higher order terms; $$u(\phi, \epsilon)=u_0+\epsilon u_1$$...
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How do I calculate the lagrangian of a planet orbiting a star and find its equation of motion? [closed]

So, it's basically what the title says. I was messing around with some systems that I found would be interesting to calculate their lagrangians, and one of these systems is a planet in an elliptical ...
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Is there difference in the curvature of light beams that pass near the BH astrophysical jet pole compared to other locations of the BH?

Is the curvature of light beams from observed nearby stars that pass near the BH slightly less when they pass above the astrophysical jet pole than when they pass at some other location of the black ...
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Why can't the degeneracy pressure self-adjust itself to resist gravitational collapse?

After a star becomes a White dwarf, it resists gravitational collapse mainly due to the electron degeneracy pressure. If the mass of the white dwarf is greater than the Chandrasekhar limit, the ...
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Doubt regarding elliptical orbits and eccentricity relation with masses

I was working with Roche's Limit , You can visit the wikipedia page on Roche's Limit and Hill's Sphere (not important here). A query raised in my mind about the elliptical orbit in which the moon is ...
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Confusions between Power spectrum and Matter Power spectrum and Relationship between the angular and 3D power spectra

From a previous post Relationship between the angular and 3D power spectra, I have got an demonstration making the link between the Angular power spectrum $C_{\ell}$ and the 3D Matter power spectrum $...
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Why doesn't the Earth's temperature increase in the perihelion?

I know that what causes seasons in earth is the tilt of the earth and the fact that sun rays reach the earth from different angles during winter and summer, but why doesn't the temperature of the ...
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Cross section for photon-electron interaction in high temperature, high density plasma

I need a plot for the cross section of the photon-electron scattering at high density and high temperature. I am working on a project for which I have to calculate the opacity of a hot, dense plasma (...
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“Weak” and “strong” spectral lines

Can some one please explain what the following excerpt from Priest's MHD of the sun means: The lowest is an extremely thin layer of plasma only several hundred kilometers thick, called the ...
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What's a scaling relation in cosmology/astrophysics?

I've seen the term around a bunch of times... But I can't find much information over the internet. As far as I know, it describes a strong correlation between two physical variables, but I'd like to ...
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What causes neutrino thermal radiation?

Often in astrophysics, I see neutrino particles being considered as photons, in the sense that hot material emits neutrino thermal radiation. There are a lot of similarities of neutrino and photon ...
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Angular momentum orientation of the orbits of the two stars with respect to the Solar System

Happen to see this in Wiki... The astronomer Karl Schwarzschild observed the motion of pairs of stars orbiting each other. He found that the two orbits of the stars of such a system lie in a plane, ...
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Is a small fragment of a white dwarf stable? [duplicate]

Assuming it is somehow possible to get a small piece of a white dwarf (maybe a dice) and this piece escapes into free space. Would that piece of white dwarf matter keep its density/state, or would it ...
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Does the Oort cloud act as a kind of shield for the Solar System?

Does the Oort cloud act as a kind of shield for the Solar System? When an interstellar object impacts the cloud, does its momentum get absorbed substantially?
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Do solar winds / mass ejections produce thrust on sun?

For every action there's a contrary reaction, so can those mass ejections make the sun move? Of course, the mass of the sun is immensely bigger than what's being eject but even being trillions of ...
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If an astrophysical jet contains gamma rays does it mean that at the source poles there is small gravitational redshift?

If an astrophysical jet contains gamma rays does it mean that even though the source has incredibly strong gravitational pull, at the source poles there is small gravitational redshift? Maybe there is ...
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Disc mass from integration of surface density as surface density changes with with radius

An accretion disc with surface density $Σ$ scales with radius $r$ as $$\Sigma=\Sigma_0 \left( \frac{r}{R_0}\right)^{-3/4} $$ where $\Sigma_0$ is the surface density at radius $R_0$ How do I integrate ...
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A formula that seems to involve the variation coefficient

A friend walking in Minsk, Belarus, found this mural from the Soviet period and sent me an image (see below) of it, asking me what the formula in it was referring to. From my naive reading (which ...
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Number of stars in Ambartsumian's Knot NGC 3561 Galaxy

Is there any data on what kind of stars and how many are in Ambartsumian's Knot dwarf Galaxy? Is there a database to refer to? Thanks in advance
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Total number of observable light sources in cosmology

Suppose we have an FLRW Universe with metric $$ds^2 = -dt^2 + a(t)^2\left(\frac{dr^2}{1-Kr^2}+r^2d\Omega^2\right) = -dt^2 + a(t)^2\left(d\chi^2 +S_{K}^2(\chi)d\Omega^2\right) $$ that is filled with ...
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Is there linear 'frame dragging'?

Very massive objects cause the so called 'frame dragging' that can increase the speed of a beam of light to a total aggregate speed faster than the speed of light in normal circumstances so my ...
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Econometrics and Astrophysics: can you help me on light curve analysis here?

Well, I'm trying to find computational algorithms to analyse light curves of quasars. My advisor suggested things like, neural networks, ARIMA algorithm, genetic algorithms and so on. But the question ...
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Does a star's emitted energy equal the work of its gravitational field?

Based on the formula of this question, it is possible to estimate the difference of the Sun's gravitational potential energy now and after it becomes a white dwarf. $$\Delta E = GM^2\left (\frac{1}{r_{...
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What exactly is Landau Damping?

I would like to understand what exactly happens when Landau damping takes place. I have seen the mathematics of it. But I am not sure If I truly understand what happens when we are talking about ...
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Equations of state for white dwarf stars

I am dealing with some model describing the given composition of a white dwarf made with photons, degenerate electrons, positrons and ions. From that, I can get tabulated values of densities ranging ...
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Computation of relation between angular power spectrum and matter power spectrum

How to write the 3D power spectrum, $\mathrm{P}(\mathrm{k})$, as an integral of the angular power spectrum, $\mathrm{C_\ell}$ ? I have the following equation, $$ C_{\ell}\left(z, z^{\prime}\right)=\...
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General Relativistic Contribution to Synchrotron Polarization

I was hoping to ask for a more "intrinsic" explanation of the relativistic contribution to the polariazation. In the same way, one can "visualize" the light bending that is caused ...
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How to calculate the variance on the ratio of 2 angular power spectra?

In the context of Survey of Dark energy stage IV, I need to evaluate the error on a new observable called "O" which is equal to : $$ O=\left(\frac{C_{\ell, \mathrm{gal}, \mathrm{sp}}^{\prime}...
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Is it justified to call the Event Horizon Telescope image of a black hole a photograph? [closed]

As this image is the result of processing data from an array of radio telescopes sensitive to wavelengths far away from the visible spectrum, to what extent can it be called a "photograph", ...
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Is there software to calculate/plot decomposed rotation curves from observational data (FITS, etc)?

I have observation data of galaxies (in FITS format). From the FITS data, I want to calculate & plot the decomposed rotation curves as pictured below. Is there a software package that will do that ...
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Frame dragging: is the velocity of the points of the 'frame' around a star inversely proportional to the square root of distance from the star?

Is the velocity of the frame around a star inversely proportional to the square root of distance from the star? In other words does it move simmilarly as astrophysical objects like planets or comets ...

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