Skip to main content
91 votes
Accepted

Is there a star over my head?

Summary There's a 1 in 500 billion chance you're standing under a star outside the Milky Way, a 1 in 3.3 billion chance you're standing under a Milky Way star, and a 1 in 184 thousand chance you're ...
MichaelS's user avatar
  • 858
46 votes

Why is the Sun's density less than the inner planets?

The sun isn't the same density all the way through. According to MSFC's solar interior page, the core density at the centre of the sun is a whopping 150,000 kg/m$^3$. Surrounding it the radiative ...
Andy's user avatar
  • 2,467
37 votes
Accepted

At the Big Bang, when everything was close together, why did it not "collide", violating Planck length or Pauli Exclusion Principle?

The Pauli Exclusion Principle forbids two indistinguishable fermions occupying the same quantum state. It does not prevent them getting arbitrarily close together so long as they have very different ...
ProfRob's user avatar
  • 153k
31 votes

Why is the Sun's density less than the inner planets?

Fusion inside of a star affects the sun's density (which does not happen with a planet). It produces an outward pressure that balances against the attraction of gravity, thereby reducing the density ...
called2voyage's user avatar
  • 6,322
23 votes

Why is the Sun's density less than the inner planets?

The density of matter depends not only on its composition, but also on temperature and pressure. It's not meaningful to say that substance A is denser than substance B without specifying the ...
Ilmari Karonen's user avatar
23 votes

Are there any planets or moons denser than Earth?

I feel it's a cheap answer but heavy Jupiters can get much denser than Earth because planets with Jupiter's mass stop adding size as they add more mass. A planet with Jupiter's size and 10-12 times ...
userLTK's user avatar
  • 24.1k
18 votes
Accepted

What is the most dense object in the universe?

Let us define this as the largest observable density of a stable object, in order to exclude black holes which may have a very large (infinite) density at their centers or objects collapsing towards ...
ProfRob's user avatar
  • 153k
16 votes

Is there a star over my head?

In short: no one knows for sure, but currently it looks that the probability is 1. Longer: On our current understanding, the Universe is probably infinite in space. This depends on the recent WMAP ...
peterh's user avatar
  • 3,161
15 votes

Why is the Sun's density less than the inner planets?

I'd say the most important answer is because the volume of stars is counted differently than for (inner) planets.For the former, most of the gas surrounding the dense core is counted. The latter don't ...
kaay's user avatar
  • 259
10 votes
Accepted

Why is the core of a gas giant supported by electron degeneracy pressure instead of nuclear fusion?

The test to see whether degeneracy pressure is going to be significant is to compare $kT$ with the Fermi energy $E_F$ The Fermi energy is the energy level up to which all energy states would be ...
ProfRob's user avatar
  • 153k
10 votes
Accepted

Size of Saturn's ring material

The vast majority of the particles in Saturn's rings are small, on the order of $\sim10^{-1}$ m or lower. The columnar number density, according to data from Voyager 1 and Earth-based observations, ...
HDE 226868's user avatar
  • 36.6k
10 votes
Accepted

Are white dwarf stars supported by proton degeneracy as well?

Straightforwardly no. For a start there are almost no free protons inside a white dwarf. They are all safely locked away in the nuclei of carbon and oxygen nuclei (which are bosonic). There are a few ...
ProfRob's user avatar
  • 153k
10 votes

Can "rogue" supermassive black holes be made this way?

I assume you're asking about central supermassive black holes (SMBHs, one per galaxy), not stellar-mass black holes. The answer is yes, but what actually happens is the two SMBHs have to merge first, ...
Peter Erwin's user avatar
  • 17.1k
9 votes

Is there a star over my head?

Does "overhead" mean over the center of your head, or over some part of your head? If we assume the latter, it changes the problem! I don't want to recapitulate all MichaelS's lovely work above, so I'...
jeffB's user avatar
  • 380
9 votes
Accepted

Are there any planets or moons denser than Earth?

From the Wikipedia page on Chthonian planet: Transit-timing variation measurements indicate for example that Kepler-52b, Kepler-52c and Kepler-57b have maximum-masses between 30 and 100 times the ...
sno's user avatar
  • 1,456
9 votes
Accepted

Are red dwarfs really 30-100 times our Sun's density?

Red dwarfs, depending on your definition, can range from 2.5 to 150 times more dense than the Sun. What is the cause of this discrepancy? They give no calculations, so I can only guess. The article ...
Schwern's user avatar
  • 514
8 votes

Why isn't the Sun hollow?

As the surface of the earth is solid the crust, Correct. underneath the crust the mantle which is liquid, No the mantle is also solid, although more plastic than the crust. There is a liquid ...
James K's user avatar
  • 123k
7 votes

Are white dwarf stars supported by proton degeneracy as well?

Proton degeneracy is not important, because its effect is much smaller -- much like nuclear particles in theory also are dictated by gravity, but the electromagnetic and nuclear forces are dominating, ...
nataliaeire's user avatar
5 votes

Why is the Sun's density less than the inner planets?

All the other answers address the density of the sun, but I feel that none of them actually addresses the OP's misconception. OP seems to think denser material should sink, but this is not the case. ...
Level River St's user avatar
5 votes
Accepted

Unbelievably high masses/ densities in NASA website data

Starting from the index you mentioned, I clicked through the links for some individual planets, which in turn link to discovery papers or other relevant observations. For planets around Kepler-23, -24,...
HDE 226868's user avatar
  • 36.6k
5 votes
Accepted

what determines the density of atmospheres

Most simply, the density is determined by the number of molecules, the surface area of the planet, the temperature, and the gravity. But it sounds like what you really care about would be called the "...
Ken G's user avatar
  • 5,336
5 votes
Accepted

Black hole density

We can understand gravity as following a set of mathematical equations called "General Relativity" which were discovered by Einstein (and others) around the start of the 20th century. The same ...
James K's user avatar
  • 123k
5 votes

Black hole density

It's simply because you can "get closer" to it, that's all. No special sauce. You know how gravity is pretty weak far away, and gets stronger close by? The closer you get to the Sun - more ...
Florin Andrei's user avatar
5 votes

Is there a star over my head?

Probably, maybe. There are at least two ways of answering the question. One is to ask what were your coordinates when you wrote the question and exactly what time it was. Then we'll need to draw a ...
keparo's user avatar
  • 151
5 votes

Can a planet exist with the same mass as the earth, but have a different diameter?

Yes, a planet can exist with the same mass as Earth, but have a different diameter - if it has a different density. The lower the density, the larger will be the diameter. In terms of an exact formula,...
The_Sympathizer's user avatar
5 votes
Accepted

Factors included in the average density of planets

Whether of not you include the mass of the atmosphere doesn't matter much. For instance, the mass of Earth's atmosphere is roughly $10^{-6}$ of Earth's mass, corresponding to the uncertainty in the ...
pela's user avatar
  • 38.6k
5 votes

If a black hole has the same mass as me, then why dont i suck everything at my center of mass?

Because you are somewhat larger than your Schwarzchild radius. In order to turn into a black hole and start experiencing exciting things like Hawking radiation, you'd need to be compressed down into a ...
Mark's user avatar
  • 3,393
5 votes

Does the density of a black hole decrease after releasing a large amount of Hawking radiation?

The smaller a 'regular', stellar-mass black hole is, the denser it is inside of its event horizon, correct? Yes, that's correct. But the black hole density is a mean density, that is, it's just the ...
PM 2Ring's user avatar
  • 14.8k
4 votes

What is the minimum mass required so that objects become spherical due to its own gravity?

Beside of mass, the rotation also affects the shape of an object. The faster the object spins, the more oblate (like a flattened sphere) it is. This happens due to the centrifugal force at its equator....
Walker Bill's user avatar
4 votes

What is the minimum mass required so that objects become spherical due to its own gravity?

It collapses onto itself, becoming more spherical. This process is called Gravitational collapse, and for a cloud of dust, will happen when the dust cloud is greater than the Jeans mass. Megan ...
Dewi Morgan's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible