[quote="Chris Peterson" post_id=303269 time=1592402832 user_id=117706]
There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect [i]where [/i]stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.[/quote]
[list]No star could form without first dissipating a great deal of angular momentum through electromagnetism:[/list]
[quote=https://en.wikipedia.org/wiki/Herbig%E2%80%93Haro_object]
[float=left][img3=HH objects are formed when accreted material is ejected by a protostar as ionized gas along the star's axis of rotation, as exemplified by HH 34.]https://upload.wikimedia.org/wikipedia/commons/thumb/d/de/Protostar_HH-34.jpg/800px-Protostar_HH-34.jpg[/img3][/float]
<<Herbig–Haro (HH) objects are bright patches of nebulosity associated with newborn stars. They are formed when narrow jets of partially ionised gas ejected by stars collide with nearby clouds of gas and dust at several hundred kilometres per second. Herbig–Haro objects are commonly found in star-forming regions, and several are often seen around a single star, aligned with its rotational axis. Most of them lie within about one parsec (3.26 light-years) of the source, although some have been observed several parsecs away. HH objects are transient phenomena that last around a few tens of thousands of years. They can change visibly over timescales of a few years as they move rapidly away from their parent star into the gas clouds of interstellar space (the interstellar medium or ISM). Hubble Space Telescope observations have revealed the complex evolution of HH objects over the period of a few years, as parts of the nebula fade while others brighten as they collide with the clumpy material of the interstellar medium. [/quote]
[quote=https://en.wikipedia.org/wiki/H_II_region]
[float=right][img3=NGC 604, a giant HII region in the Triangulum Galaxy]https://upload.wikimedia.org/wikipedia/commons/7/7a/Nursery_of_New_Stars_-_GPN-2000-000972.jpg[/img3][/float]
<<An HII region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically a cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm. The Orion Nebula, now known to be an HII region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered.
The precursor to an HII region is a giant molecular cloud (GMC). A GMC is a cold (10–20 K) and dense cloud consisting mostly of molecular hydrogen. GMCs can exist in a stable state for long periods of time, but shock waves due to supernovae, collisions between clouds, [b][u][color=#0000FF]and magnetic interactions can trigger its collapse[/color][/u][/b]. When this happens, via a process of collapse and fragmentation of the cloud, stars are born (see stellar evolution for a lengthier description).
As stars are born within a GMC, the most massive will reach temperatures hot enough to ionise the surrounding gas. Soon after the formation of an ionising radiation field, energetic photons create an ionisation front, which sweeps through the surrounding gas at supersonic speeds. At greater and greater distances from the ionising star, the ionisation front slows, while the pressure of the newly ionised gas causes the ionised volume to expand. Eventually, the ionisation front slows to subsonic speeds, and is overtaken by the shock front caused by the expansion of the material ejected from the nebula. The HII region has been born.
The lifetime of an HII region is of the order of a few million years. Radiation pressure from the hot young stars will eventually drive most of the gas away. In fact, the whole process tends to be very inefficient, with less than 10 percent of the gas in the HII region forming into stars before the rest is blown off. Contributing to the loss of gas are the supernova explosions of the most massive stars, which will occur after only 1–2 million years.>> [/quote]