 Whether due to collisions with a spiral arm , or through the shock wave emitted from supernovae , the atoms are precipitated into heavier molecules and the result is a molecular cloud . This presages the formation of stars within the cloud , usually thought to be within a period of 10 @-@ 30 million years , as regions pass the Jeans mass and the destabilized volumes collapse into disks . The disk concentrates at the core to form a star , which may be surrounded by a protoplanetary disk . This is the current stage of evolution of the nebula , with additional stars still forming from the collapsing molecular cloud . The youngest and brightest stars we now see in the Orion Nebula are thought to be less than 300 @,@ 000 years old , and the brightest may be only 10 @,@ 000 years in age . 
