|WikiProject Solar System||(Rated C-class, Mid-importance)|
|WikiProject Astronomy||(Rated C-class, High-importance)|
I think the spelling of 'disc' should be changed to 'disk', both in the title of this page, and in all references. In common american english usage, the word disk is usually spelled with a k. The only common use of the c spelling is for compact discs. Furthermore, in my astronomy background, in english publications I never see the word disk spelled with a c, whether its protoplanetary disk, accretion disk, disk of a spiral galaxy (galactic disk), etc. Myrrhlin 19:43, 17 March 2006 (UTC)
You have never read the Monthly Notices of the Royal Astronomical Society, then.
The main article would be improved a lot if there were some kind of absolute numbers associated with the materials that eventually fall into the accretion disk.
Assuming that the mass of material we are dealing with, is four or five times the mass of the sun, and distributed evenly in a spherical volume four or five times wider than the distance from the Sun to Pluto, what absolute velocities are going to be realized at any given time in the course of the volume's collapse? At what point in time does this large, amorphous volume assume the shape of a disk, assuming the mass is at rest with itself, and not interfered with from afar.
Some fifteen or twenty years ago, I read an article in Scientific American magazine where the author was of the opinion that the time of the Sun's accretion could have been as brief as 50,000 years. The article begs the question why an amorphous mass would necessarily assume a disk shape unless there were a significant partiality in angular momentum at the very start of the volume's collapse. Alternatively, the volume might assume a particular angular momentum if a foreign object passed through the middle of the volume, running right through it.
What figures (relative to the escape velocity) can be arrived at, assuming that the overall dust enjoys some kind of rotational speed around a broad common center, and is subject to more or less continuous (if not constant) gravitational acceleration?
In the same way that weather systems and hurricanes are spun. Is it not more feasible that the discs rotation is attributable to the distance from the galactic center on the inside of the disc to the outside of the disc?
Whilst only approximately 8 light hours in diameter, making the relative distance negligible to the 28000 light years the sun is from the galactic center, the relative velocity of the upper and lower atmosphere also yield a negligible relative distance compared to the velocity at which weather systems rotate. Yet in both cases, the relative velocity of rotation is about 10% of the orbital rotation, 120 km/h for wind with earths rotation of 1666 km/h, 100,000 km/h for the earth with the solar systems galactic orbital velocity of 828,000 km/h. Did the protoplanetary hot disc behave more like a liquid or a gas? Andrew M. Cross (talk) 13:54, 13 November 2015 (UTC)
Shape, Density Gradient
I arrived at this page in the course of doing some research on the early solar system. What I'm looking for is some kind of characterization of the distribution of matter in a protoplanetary disk. I want to know how flat the disks usually are and how the material making them up is distributed. This would be very useful information to include in this article. Perhaps someone could augment the article by providing some information on this. Kevin Langdon 15:46, 26 April 2007 (UTC)
There is a serious error in the first paragraph, as if someone screwed up while cutting and pasting or fell asleep on their keyboard: "accretiRuimtetelescoop Hubbleon". I'm not sure what is supposed to go here. Wikipedia suffers a lot from this kind of thing.
Hubble's recent observations
As these observations are mentioned in the article, someone might want to add a few images of these observations (30 images of proplyds in the Orion Nebula have been released), or a link to this gallery on Commons. Grand Schtroumpf (talk) 14:07, 19 December 2009 (UTC)
The paragraph below was removed. The first statement "water is the only known substance found in planetary disks in both the solid (ice) and gaseous phases" is wrong. Carbon monoxide (CO) is also found in both states abundantly. In addition, the reference given corresponds to a conference abstract (no article).
Water is the only known substance found in planetary disks in both the solid (ice) and gaseous phases together in large quantities. Consequently, determining their relative proportions is useful in characterizing the physical state of a nebula and the planet formation process. Typical protoplanetary disks are composed of a wide range of densities and temperatures, which results in an array of gas/ice ratios. Ice predominates far nebula and mid nebula while gaseous water tends to dominate the centerplane area of the near nebula and above the disk photosphere.(Davis 2006)
The paragraph below was removed. It is irrelevant: protoplanetary nebula is never used in astronomy to design a protoplanetary disk. Although there is an abiguity on the word "protoplanetary" for historical reasons, protoplanetary nebula always refers to an evolved (old) star.
The name protoplanetary nebula is sometimes employed (for example in Davis 2006) when discussing protoplanetary disks. However, this can lead to confusion with the same term subsequently being also employed when discussing the unrelated concept of planetary nebulae. (See protoplanetary nebula for more information on naming.)
Origin of theory and relation to discovery of phenomenon
Is there any discussion to be had on the development of ideas about the protoplanetary disc, if the idea was in place before such phenomenon was discovered? I think these are important questions to ask when it comes to astronomy, particularly cosmology. Giving us, not only meaningful background and history, but also insight into the workings of our scientific community. If anyone has this kind of information, please let me know --IronMaidenRocks (talk) 02:12, 21 November 2014 (UTC)
Thick or thin
The article says: "Protoplanetary disks are thought to be thin structures, with a typical vertical height much smaller than the radius, and a typical mass much smaller than the central young star." This looks wrong for several reasons. First, such disks were once modeled one-dimensionally, as if they were infinitely thin. The latest research suggests that they are more likely to be very, very thick. The second problem is the definition of "thin" given here, as vertical height very much smaller than the radius. That's a terrible definition of "thin" since even an extremely thick disk would fit that definition. Zyxwv99 (talk) 23:03, 25 March 2016 (UTC)
Mechanics of formation
How does a system go from cloud of particles moving in a variety of directions, to a disc where most are rotating in the same plane in the same direction? Is it only through collisions and close encounters that angular momentum is averaged out into a net spin? Once a disc starts forming, does the gravity of the dominant plane exert sideways pull on the orbits of particles outside the plane until they all align? I think I wrote that on a planetary science quiz once and got it marked wrong for one part or the other. This question has been bugging me for decades. Beland (talk) 19:23, 28 September 2016 (UTC)