Questions tagged [density]
A measure of the ratio of an object's mass with its volume.
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How to find the accretion rate required to power the Sun?
If The potential energy of the Sun is:
Ep =3GM^2/5R
PROVIDED that the density is constant.
prove that the accretion rate required to power the Sun is:
dM/dt = 2 ...
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1answer
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Why the forbidden lines of [OIII],[NII] and [SII],[OII] are sensitive to electron temperature and electron density, respectively?
I am trying to understand the topic of "Metallicity estimates", either HII regions or planetary nebula. For this latter, the electron temperature (and density) must be known. I am studying the ...
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Are there any known asteroids with average density similar to that of Earth's?
In this answer I mention that for very low orbits around spherical bodies, the period tends to scale only as the inverse square root of the density, and not the diameter.
For a low orbits where the ...
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Can “rogue” supermassive black holes be made this way?
Could two galaxies (one big and one small)intersect at a velocity to allow the smaller black hole to escape but not the galaxy around it?
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Why isn't the Sun hollow? [closed]
[Edited to remove incorrect geological assumptions]
The sun is self-rotating, i.e. it spins on its axis. When something spins, there's an apparent force away from the centre, and matter gets flung ...
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2answers
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Does Flat Universe mean even distribution?
I've read through all the other related answers to "flatness" questions but I need a bit more clarification.
I understand that a triangle in a 2D universe would not equal 180 degrees in both a closed ...
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1answer
115 views
Does the sun blow a bubble into the interstellar medium?
I once read that the solar wind is more or less blowing a "bubble" into the interstellar medium. However, the numbers I found while trying to verify this don't give me a clear picture yet:
The ...
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2answers
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Question about $3p/c^2$ in Friedmann equation
The Friedmann Equation:
$$\frac{\ddot{a}}{a} = -\frac{4\pi G}{3}\left(\rho + \frac{3p}{c^2}\right) + \frac{\Lambda c^2}{3}$$
I want to know, where does the $3p/c^2$ come from. I know it is something ...
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How To Determine Planetary Differentiation Through Density, Mass and Size?
How can I accurately predict a body's composition and structure using only density, mass and the size (diameter) of the body?
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1answer
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Approximating density of hydrogen in [observable] universe
Let universe be completely made from hydrogen. And also we have redshift $z= 6$. with Hubble constant $H_{0} = 2.1941747572815535\times 10^{-18}\:\mathrm{s}^{-1}$. We also know that density of the ...
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1answer
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Finding equation for energy density of matter
I'm trying to get an equation for the energy density of matter of the universe $\rho(t)$, assuming the number of particles is conserved and rest mass energy is much greater than kinetic energy. $\rho(...
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1answer
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Equating critical energy density to matter density
I'm asked first to calculate the critical energy density $\rho_{crit}$ of the universe given certain constants. The value I got was $5500\,\mathrm{MeV}\,\mathrm{m}^{-3}$.
Then I'm asked to calculate ...
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1answer
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Does our current understanding of the mass of black hole only allow for it to be located at the singularity? [duplicate]
Does the distribution of mass or density of mass inside the event horizon matter for a black hole to exist as we currently theorize? Could the mass inside the event horizon be distributed in any way ...
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What's the density of dark matter (clouds)?
How much mass per unit volume do known dark matter have, for instance in the Bullet Cluster? Does the density vary in space, for example, do individual dark matter structures have denser cores?
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2answers
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Why is there a density dropoff in the stellar winds of magnetic O-type stars?
I recently went to a talk on X-ray emissions from stellar winds of O-type stars, and a paper was explored that in turn referenced ud-Doula et al. (2014).
Essentially, O-type stars may show strong x-...
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Size of Saturn's ring material
How big are the chunks of rock ice that make up Saturn's rings? Are there many objects larger than pebble size?
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NFW Profile for Seyfert Galaxies
I would need to know the NFW (or similar) profiles of several galaxies/clusters to estimate the line of sight Dark Matter column densities. I have found them in a couple of cases, but not for many ...
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1answer
322 views
What's the theoretical maximum density of a galaxy?
In watching this Hubble video on Omega Centari it got me thinking about how dense a galaxy can get. Do we know how dense a galaxy can get?
Are there any good resources on reading more about very ...
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2answers
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Are white dwarf stars supported by proton degeneracy as well?
In general, fermions form a degenerate gas under high density or extremely low temperature. It's clear that white dwarf stars are supported by electron degeneracy pressure. However, there are still a ...
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2answers
635 views
Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?
After a Sun-sized protostar forms, its core will become denser over time due to radiation. The core eventually gets dense and hot enough for hydrogen fusion to take place. In the late phases of the ...
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1answer
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What is the most dense object in the universe?
Inspired by this answer to the question, Why is the Sun's density less than the inner planets?, what is the most dense object in the universe?
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Why is the Sun's density less than the inner planets?
The density of the Sun is $1410~\frac{\text{kg}}{\text{m}^{3}}$ and Mercury's is $5430~\frac{\text{kg}}{\text{m}^{3}}$, but shouldn't the Sun be denser? Because when the Solar System was forming, ...
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1answer
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How do star densities work?
If we take a look at stars more massive than the Sun, their densities vary a lot. UY Scuti is an extremely low-density star that's only 8.5x more massive than the Sun, but is 1000-2000x its size. ...
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Planets classification by density
In our Solar system, the density of major planets varies from 0.7 g/cm3 (Saturn) to 5.5 g/cm3 (Earth).
For exoplanets, the density varies from very low (0.03 g/cm3 for Kepler-51x) to very high (77.7 ...
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1answer
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Unbelievably high masses/ densities in NASA website data
In May, I did my own amateur analysis of Kepler data that was supplied here. This was a table of all confirmed "Kepler planets" to date (April 1, 2015). This table had some unbelievably high masses/...
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Radial Density Profile Equation [closed]
The Virgo Galaxy Cluster has a mass of $10^{14} M_{\odot}$ and its centre is $16Mpc$ from Earth. The large elliptical galaxy $M87$ lies at the centre of the Virgo cluster. $M87$ has a supermassive ...
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1answer
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Why are the high density regions in outer space black holes?
The escape velocity of an object is given by the following formula.
$$v_e=\sqrt{\frac{2GM}{r}}=\sqrt{\frac{2 \mu}{r}}= \sqrt{2gr}$$
As far as I am aware, the mass of the star which formed the black ...
3
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1answer
605 views
Why is [O III] a good density probe in interstellar medium?
According to Draine in his book "Physics of the interstellar and intergalactic medium" (page 210/211) and Caltech [O III] line ratio's (amongst others) are a good density probe, but I cannot really ...
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2answers
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Maximum and minimum gas giant & ice giant densities
I'm working on a star system generator for a game; I'd like its results to be plausible but they needn't be super-realistic. I've got the orbital distances and masses of each body in the system, and ...
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3answers
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What is the minimum mass required so that objects become spherical due to its own gravity?
Is this minimum mass known? or maybe, is it given in terms of density? If so, how much density is the minimum to have an spherical object due to its own gravity?
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1answer
600 views
What is the current accepted theory as to why Mercury, despite its size, has a similar density to Earth?
According to the NASA web page overview about Mercury, despite the planet being just a bit larger than our moon, it's density is about 98.4% of Earth's. This high density suggests a comparatively ...
