Questions tagged [density]
A measure of the ratio of an object's mass with its volume.
3
votes
4answers
712 views
Black hole density
How does more compression relate to a stronger gravitational pull. Like, when we say that a black hole is a tiny space that has 20-30 suns compressed in it, how does this increase its density and ...
5
votes
1answer
62 views
what determines the density of atmospheres
What factors determine the atmospheric density on various planets and moons? Some larger bodies have less dense atmospheres, while some smaller ones have a more dense atmosphere.
1
vote
1answer
36 views
From original burst, fraction of stellar mass still surviving on Main sequence
Suppose that all stars in this galaxy were born in a single major-merger burst event about 10
Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars ...
0
votes
1answer
40 views
number density of Dark Matter Halos Versus number density of Galaxies
Can we count only one dark matter halo for each Galaxy ?
Indeed, I am trying to estimate the total density of galaxies in given volume and I have often seen on physics exchange and other forums the ...
3
votes
1answer
119 views
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 ...
0
votes
1answer
38 views
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 ...
8
votes
3answers
228 views
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?
-4
votes
2answers
244 views
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 ...
4
votes
2answers
109 views
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 ...
6
votes
1answer
130 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 ...
3
votes
2answers
87 views
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 ...
0
votes
1answer
219 views
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 ...
1
vote
1answer
437 views
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(...
2
votes
1answer
124 views
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 ...
0
votes
1answer
102 views
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 ...
1
vote
0answers
76 views
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?
1
vote
2answers
57 views
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-...
6
votes
2answers
1k views
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?
1
vote
1answer
468 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 ...
9
votes
2answers
787 views
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 ...
6
votes
2answers
775 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 ...
11
votes
1answer
3k views
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?
30
votes
6answers
9k views
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, ...
6
votes
1answer
4k views
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. ...
1
vote
1answer
1k views
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 ...
6
votes
1answer
123 views
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/...
-2
votes
1answer
460 views
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 ...
1
vote
1answer
159 views
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
votes
1answer
679 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 ...
6
votes
2answers
1k views
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 ...
11
votes
4answers
7k views
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?
13
votes
1answer
668 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 ...
