I challenge the idea that gravitational collapse can happen from gases in a nebula due to "self-gravity." Consider the following. From Hawking and Penrose : "The instability of gravitation is not manifest under normal conditions owing to the extreme smallness of the gravitational constant. The pull of gravity is readily counteracted by other forces."distefanom wrote:"Collapsing due to self-gravity..."
I was wondering if this isn't a way too simple explanation to [cause] these clumps of matter...
even at these space scales couldn't it be that there are acting also *other* physical phenomena?
The standard theory of planet formation does not explain sufficiently how it is that gravity overcomes the coulomb force between atoms in the protostellar disk of gases to form the minerals and molecules of rocky material.
A dense area of a nebula will attract more matter, but there is a limit to how dense the region as a whole can become. In a nebula, each little cubic centimeter of gas experiences the gravitational pull of its close neighbors in such a way that distant matter does not affect it much (gravity is proportional to 1/r2, the inverse square of the distance between different cubic centimeters). Additionally, atoms in the gaseous nebula have small charge imbalances that cause them to repel each other; thus, they do not get close enough to form a gravitational instability. Therefore, a dense part of a nebula is not going to trigger gravitational collapse.
The orthodox thinking about star formation, treats all the mass within a 1-2 light year sphere of nebula gases as residing at the center of mass. In physics, the ability to consider all mass as residing at a point at the "center of mass" is:
a) due to how the calculus (math) of the calculation works out, and
b) appropriate for looking at the center of mass of one object versus another object that is at a distance r from the first object, not necessarily a continuous sphere of matter.
Chris, is reporting the state of the way things are in space-science. However, I offer these three empirical facts that contradict his belief and the belief of others that "our understanding of the mechanisms involved is accurate."Chris Peterson wrote: It also happens that there are numerical simulations of gas and dust structures, and they demonstrate that gravity alone explains the way they collapse. That is, the models and our observations of natural structures are closely matching, which is strong evidence that our understanding of the mechanisms involved is accurate.
1. Planet-finding observatories in space, such as the Kepler planet-hunter, have found planets that are too close to their respective stars to have formed the way that the standard model says. https://apod.nasa.gov/apod/ap131105.html
2. Space scientists who have studied the center of the Milky Way see a group of stars that should not have formed so close to the black-hole center if the standard model is correct. "The problem is that according to standard scenarios of star formation and stellar dynamics the stars cannot be born in such an extreme environment because of the strong tidal shear, but are also too short-lived to have migrated there from farther out." [See Eisenhauer et al. (2005)]
3. Young Star Object CX330 went from black hole to observable young star object (CX330) within 3 years, 2007 Spitzer infra-red [left] to 2010 NASA's Wide-field Infrared Survey Explorer (WISE) [right]. [Reference: Maccarone, et. al 2016]
https://www.kickstarter.com/projects/76 ... nce-theory).