A Star is Born

Caption: the Pillars of Creation, dark cloud remnants of a giant molecular complex backlighted by reflection nebulae illuminated by bright young stars. Some evidence suggests that this complex has already been blasted apart by a supernova still enshrouded in dust. Definitive evidence should reach us in a thousand years or so.

So you say you want to be a star. A lot of success in anything is about being in the right place at the right time. In the case of becoming a star, that place is in a galaxy with sufficient dust and gas, and getting down to the nitty gritty, being in a massive molecular cloud complex, in one of the cores of such complexes. Such clouds are the coldest (10-30K) and densest parts (up to 10^6 molecules/cm^3) of the interstellar medium - the gas and dust that occupies the space among the stars. The big ones have masses from thousands to millions of times the mass of our Sun.

It seems to be only in these massive, cold, and dense clouds that gravity can overcome pressure and compress the gas enough to produce star formation. Typically, these clouds produce star broods of hundreds to tens or even hundreds of thousands of stars at a time. The masses of the stars produced vary from a less than a tenth of the mass of the Sun to about 100 times as massive as the Sun. Everything moves faster for the biggest stars: condensation from gas and dust to ignition of hydrogen burning takes only tens of thousands of years. Birth to death may take only ten million years, at which point their smaller siblings are just getting round to stellar ignition.

The big guys are not docile cribmates. As soon as they light up the UV radiation from these starts disrupting the molecular hydrogen and ionizing it. When these brief candles are through strutting and fretting their time upon the stage they blow themselves up in type II supernovae, blasting apart the stellar nursery, though incidentally compressing parts of it to trigger more star formation.

If you are medium sized star of one solar mass or so, though, and manage to form without getting disrupted, you can look forward to ten or so billion years on the main sequence before your own somewhat quieter senescence (becoming a red giant, and finally, a white dwarf.) During that time your cluster of crib mates will gradually be disrupted by the gravitational tugs and shocks of close encounters, eventually losing touch with all your siblings.


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