"Initially, a massive cloud of gas contracts under its own gravity. Internal gas molecules radiate heat away, enabling further shrinking. The densest areas fragment first, diminishing further in size."
"As protostellar growth continues, gravitational potential energy converts into heat. Powered by gravity, these protostars shine: long before fusion initiates. As their interior temperatures rise, proton-deuterium fusion begins."
"For 'star birth,' the rate of fusion must balance the star's luminosity: its total power output. Energy balance and growth cessation, not ignition, dictates stellar birth."
Star formation begins with a massive gas cloud contracting under gravity. As it shrinks, internal heat is radiated, leading to fragmentation. The densest regions form protostellar clumps, which shine due to gravitational energy before fusion starts. Below 0.075 solar masses, brown dwarfs form, while higher masses initiate proton-dominated fusion. For true stellar birth, fusion must balance luminosity. Massive stars contract rapidly, being born in about 30,000 years, while sun-like stars take around 50 million years. Official birth occurs at the zero-age main sequence when energy balance is achieved.
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