Posted on 04/30/2008 8:00:18 AM PDT by RightWhale
If left to gravity alone, it isn't very likely that material in our sparse universe would ever just collapse in on itself to form stars.And both you and Wendy are aware (I hope) that the universe wasn't always as roomy as it is today.
Right. I didn't claim otherwise. But something first needs to 'sweep' the gas and dust together so that gravity can then take over and cause the collapse and eventual nuclear reactions that make a star a 'star'. (at least in many cases this is true--I just learned you were right and stars DO collapse under their own weight more often than I suggested, given enough time)
"Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds. These regions are extremely cold (temperature about 10 to 20K, just above absolute zero). At these temperatures, gases become molecular, the group together. CO and H2 are the most common molecules in interstellar gas clouds. The deep cold also causes the gas to clump to high densities. When the density reaches a certain point, stars form." ...
"Often in galaxies we find clusters of young stars near other young stars. This phenomenon is called supernova induced star formation. The very massive stars form first and explode into supernova. This makes shock waves into the molecular cloud, causing nearby gas to compress and form more stars. This allows a type of stellar coherence (young stars are found near other young stars) to build up, and is responsible for the pinwheel patterns we see in galaxies.":
http://abyss.uoregon.edu/~js/ast122/lectures/lec13.html
You were also correct about the strange magnetic mechanism that can (or possibly can) in special situations also trigger star formation.:
"Some previously unrealized energetic process, likely related to magnetic fields, is superheating parts of the cloud, nudging it to become a star, scientists said.
The detection of X-rays from the cold stellar precursor surprised astronomers. The observations reveal that matter is falling toward the core 10 times faster than gravity could account for. 'We are seeing star formation at its embryonic stage,' said Kenji Hamaguchi, a NASA-funded researcher at the Goddard Space Flight Center. 'Previous observations have captured the shape of such gas clouds but have never been able to peer inside. The detection of X-rays this early indicates that gravity alone is not the only force shaping young stars.'" [but I don't get how 'heating' of the cloud would help it *collapse*-EOTL]:
http://www.space.com/scienceastronomy/proto_stars_050301.html
Also see:
"In the 1950's it was thought that magnetic fields could be the mysterious generators of spiral structure. However, the mechanism for how this would work was never clearly developed. Furthermore, one would expect that, if magnetic fields were behind the density organizations, the energy density of the fields would be equivalent to that of the mass gravitational energy. Subsequent observations of field strength showed it falling short by a factor of five (BT94). It is known, however, that magnetic fields follow the path of spiral arms.
The first really robust theory was developed by C. C. Lin and Frank Shu in papers of 1964 and 1966. They proposed that spiral arms were the manifestations of spiral density waves in the gas and stars of a galaxy. This theory, or variations on it, seems to be the most resilient even today."
http://casa.colorado.edu/~danforth/science/spiral/
OK, enough of this (for now). I've gotta focus on tommorrow's Kentucky Derby! :)
Good post. Well done. I’m going to read your links later today.
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