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1answer
63 views

Why 2007 OR₁₀ is not a dwarf Planet yet?

Per definition a dwarf planet is: a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic ...
4
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1answer
133 views

Are larger stars rounder?

The Earth is a very smooth sphere, and the Sun even more so, with only minor fluctuations. I am wondering: are larger stars even rounder? Intuitively, that seems self evident, but I am not so sure. ...
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0answers
76 views

Formulas for gravitatitional equilibrium

I am trying to calculate at which point gravitational equilibrium sets in for various bodys (planets stars neutron stars etc.) assuming they are perfect spheres. However the radius i get is not equal ...
2
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1answer
102 views

How to calculate the mean molecular weight of the Sun

I have a homework question in which I need to estimate a parameter known as $\beta_{P}$ and also the core temperature, both for the Sun. However, prior to doing this I need to know the mean molecular ...
4
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2answers
81 views

Is there a mechanism that makes small moons more rounded than comets?

67P/Churyumov–Gerasimenko has a highly irregular dumbbell shape. But the sample of comet shapes observed is very small, so I wonder if irregular shape is the norm for comets and for small moons. Many ...
4
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1answer
57 views

What happens to the Gas Pressure when working out the Eddington Luminosity?

I am looking at how the Eddington Luminosity is derived and I do no understand why we only care about $P_{rad}$? When working out $L_{Edd}$ you take the ratio between $dP_{rad}/dr$ and $dP_{...
2
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4answers
84 views

Can objects enter hydrostatic equillibrium through processes other than the influence of gravity?

Wouldn't a droplet of liquid (say water) floating around in space become spherical and "in hydrostatic equilibrium" due to surface tension but not gravity?
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2answers
292 views

How can astronomers determine the difference between “hydrostatic equilibrium” and “just happens to be spherical”?

This is relevant for the definition of a dwarf planet. I presume the answer will be, well, if we can tell the mass of the body and guess the material. I don't find this very satisfactory because (1)...
3
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1answer
107 views

What's an order-of-magnitude main sequence star look like?

I'm looking for a very rough, order-of-magnitude approach to the main sequence. What I mean is, I have a spherically-symmetric hydrogen distribution. I'm looking to get a rough approximation for ...
2
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1answer
118 views

What is the time/size/rigidity ratio for a space object to become mostly round?

In the answer here multiple comets are identified that do not form a single round body. A drop of water will form a round shape in the time it takes to free fall a couple of feet. All of the ...