subject: Birth of Star [print this page] Birth of Star Birth of Star
In this artist's conception, observers peer through thedark dust of L1014to witness the birth of a star. NASA's Spitzer Space Telescope has detected a faint, warm object inside the apparently starless core of a small, dense molecular cloud. If, as astronomers suspect, there is a young star deep inside the dusty core, it would have a structure similar to this illustration. Dark dust from the cloud, attracted by the gravity of thenewbornstar, forms a disc as it spirals inward. Often, the hidden birth of a star is heralded by bipolar outflows, jets of material moving outward from the star's poles.The formation of a star begins with a gravitational instability inside a molecular cloud, often triggered by shock waves from supernovae (massive stellar explosions) or the collision of two galaxies (as in a starburst galaxy).
As the cloud collapses, individual conglomerations of dense dust and gas form what are known as Bok globules. As a globule collapses and the density increases, the gravitational energy is converted into heat and the temperature rises. When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibrium, a protostar forms at the core. These pre-main sequence stars are often surrounded by a protoplanetary disk. Large stars consume their fuel very rapidly and are short-lived. Small stars (called red dwarfs) consume their fuel very slowly and last tens to hundreds of billions of years. Besides mass, the portion of elements heavier than helium can play a significant role in the evolution of stars. The metallicity can influence the duration that a star will burn its fuel, control the formation of magnetic fields[58] and modify the strength of the stellar wind. Older, population II stars have substantially less metallicity than the younger, population I stars due to the composition of the molecular clouds from which they formed. (Over time these clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres.)
Early stars of less than 2 solar masses are calledT Tauri stars, while those with greater mass are Herbig Ae/Be stars. These newly born stars emit jets of gas along their axis of rotation, which may reduce the angular momentum of the collapsing star and result in small patches of nebulosity known as Herbig-Haro objects.These jets, in combination with radiation from nearby massive stars, may help to drive away the surrounding cloud in which the star was formed. More information...
