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49 votes
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What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

Two rocks placed in space with no relative motion are going to be attracted by gravity, and hit. 3 rocks, placed in space with no carefully rigged symmetry, will likely miss each other, as the ...
Wayfaring Stranger's user avatar
37 votes
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Why do planets and satellites in the Solar system look so wildly different if they came from more or less the same matter?

This questions can be split in two; for planets and satellites. The diversity of planets reflects in part the diversity in terms of chemical composition of the protoplanetary disk. We know that UV ...
Swike's user avatar
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16 votes

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

The prior gas cloud will start with some small random motions and density variations left over from its formation. As a patch starts to contract any small amount of rotation gets amplified as the ...
blanci's user avatar
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13 votes

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

The answer is turbulence. Stars are formed from large gas clouds that collapse under their own weight. As they do so, they become unstable to fragmentation and break up into smaller collapsing pieces. ...
ProfRob's user avatar
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8 votes

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

Other answers good, but this question left behind: Why isn't all the disk material been swallowed by the star? Because of the excess of angular momentum carried by some particles. They insist on ...
fraxinus's user avatar
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8 votes
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Why do the solar system planets go rock-gas-ice instead of rock-ice-gas when moving away from the sun?

Prelude It is now generally accepted in the planet formation community that planets form as a side-product of the star formation process in so-called protoplanetary discs. Protoplanetary discs have ...
AtmosphericPrisonEscape's user avatar
7 votes
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Did Mercury clear its neighborhood?

One calls Mercury a planet because it doesn't share its orbit with any other bodies of comparative size. The fact that it is in its orbit means that that orbit hasn't been cleared by another body (for ...
James K's user avatar
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5 votes
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Who named Gomez's Hamburger as "Gomez's Hamburger"? (IRAS 18059-3211)

The discovery team at the Cerro Tololo Inter-American Observatory in Chile. From New Scientist: 23 Jan 1986 If British Observers are feeling a pinch, they could always take a lead from their ...
James K's user avatar
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4 votes
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Why is Earth's rotation considered fast?

The interactions of the Earth and its moon have slowed the Earth's rotation significantly over the billions of years since their formation. Wikipedia cites a paper that gives a figure of ...
BowlOfRed's user avatar
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3 votes
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Are warm circumstellar debris disks still able to be detected at sub-millimeter wavelengths?

Such surveys are designed to detect an excess of emission over that expected from a stellar photosphere. The emission from a circumstellar disk is often modelled as a blackbody at lower temperature ...
ProfRob's user avatar
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3 votes

Exoplanets, Protoplanets, and planetesimals

Whether or not gas giants form is largely to do with whether rocky/icy cores are able to accrete large quantities of hydrogen and helium, which dominate the mass of the protostellar disc. ...
ProfRob's user avatar
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3 votes

Measure the deprojected distance between two points?

@Greg Miller's point is that the rotation angle doesn't count. The only measurement you care about is the inclination. It makes a point's arc distance from the major axis of the apparent ellipse cos(...
stretch's user avatar
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3 votes
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Estimate upper limits on flux values in the case of a non-detection?

$\sigma = \delta\nu\sqrt{N}\sigma_{\mathrm{rms}}$ Channel width $\delta\nu$ is in km/s (spectral resolution) and rms is in Jy/beam (noise in channel): I imagine you already know these. $N$, the number ...
terribleGuitarPlayer's user avatar
3 votes

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

Answers, in order: Why did the protoplanetary disk start rotating around the star? Star and disk form around the same time. The rotation forms because all other orbits will cross the orbit of the disk ...
user132372's user avatar
2 votes

Protoplanetary disk luminosity - looking for a sanity check please

Yes, there's a major problem. You are trying to run a "device" that uses up $350L_\odot$ with a $1L_\odot$ power source. In fact it's worse than that because the grains cannot absorb more ...
ProfRob's user avatar
  • 155k
1 vote

Does a more massive main proto-body result in more massive satellites? More satellites?

You might be asking for something that does not yet exist. No exomoons have been detected, so correlations with planetary mass are limited to the Solar System. Planetary formation takes millions of ...
ProfRob's user avatar
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1 vote
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Measure the deprojected distance between two points?

My eventual solution was to rotate the image using the 2D rotation matrix, then deproject by accounting for the inclination. In Python, this looks like: ...
lucas's user avatar
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1 vote
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What is the meaning of grain opacity and why does it affect the formation time of gas giants?

The cooling of a gas giants outer envelope (which in turn cools the convective interior) is dominated by radiative transport. The radiative flux at the photospheric boundary is $$F_{rad}\propto- \frac{...
AtmosphericPrisonEscape's user avatar
1 vote
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What color distribution does a protoplanetary disk have?

The answer seems to be a clear "it depends": Homogenity of the disks depends on the age of the protoplanetary disk. Temperature is a function of the radius and the color-scale used in (old) ...
B--rian's user avatar
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