How Are Stars Formed?

Star formation is a unique branch of Astronomy that deals with studying Interstellar mediums and GMC's or Giant Molecular Clouds to better understand how dense regions within these clouds collapse into spheres or orbs of plasma and gases and form stars, young stellar objects and new planets. Areas with higher density form clouds or nebulae. It is from these regions that stars are born or formed. These cloud structures are also referred to as 'Stellar Nurseries' since they are considered the primary source of all new stars, celestial objects and planets. These celestial objects are then ejected from the nebulae and form galaxies. These galaxies are either spiral or elliptical in nature and can even collide with one another changing the entire dynamic of both galaxies involved in the event.
Our galaxy which is known as the Milky Way has roughly 6,000 such molecular clouds, the closest nebula to our Sun which is capable of producing new stars and planets is the Orion nebula. This region of our galaxy is approximately 1,300 light years away from the Sun itself. There are smaller, or lower mass stars being formed in a region known as the Ophiuchi cloud complex which is significantly closer, ranging roughly 400-450 light years away. Bok globules, which were named after Astronomer Bart Bok, are also regions of space from which stars can be create. These globules form during the collapse of molecular clouds and appear as opaque cloud formations which are considered more compact star producing structures.
The nebulae where stars are formed consist of different molecular clouds. If one of these molecular clouds becomes so massive that the gas pressure cannot support it, the molecular cloud undergoes gravitational collapse, which results in the fragmentation of the molecular cloud. These smaller pieces and fragments condense into rotating spheres of gas known as stellar embryos.
There are several events that can result in the compression of a molecular cloud causing its gravitational collapse and subsequent fragmentation in a process referred to as triggered star formation. The collision of molecular clouds, and explosion from a close enough supernova, as well as galactic collisions can all result in the gravitational collapse of one of these molecular cloud masses. The collision of two galaxies usually results in the massive formation of multiple stars, also called starbursts, as the molecular gas clouds from each galaxy are compressed and tossed around by tidal forces created within each separate galaxy.
Stars are generally categorized as either being low mass or high mass formations which are created by slightly different occurrences. The theory of low mass star creation is supported by observational evidence, whereas the theory of massive star formation is still being studied and observed to obtain and compile significant data which will serve to better educate Astronomers on the difference between the two different creation methods. Smaller or lower mass stars are thought to be created when the cloud collapses, releasing gas and dust which rotates in what is called an accretion disk around a centrally located protostar. The amount of material in the accretion disk ultimately determines the overall size of the star when it is completed.