What is the initial energy source that makes a protostar shine before fusion begins?
Answer
The Kelvin-Helmholtz Mechanism
A protostar, by definition, has a core temperature too low to initiate sustainable nuclear fusion, meaning energy generation cannot rely on nuclear reactions. Its initial luminosity is purely mechanical, derived from the Kelvin-Helmholtz Mechanism. This process functions because as the mass of gas continually contracts under its own gravity, gravitational potential energy is converted directly into heat and light. Approximately half of this released gravitational energy is radiated away as starlight, while the other half contributes to further heating the interior of the shrinking gaseous sphere.
Related Questions
What is the initial energy source that makes a protostar shine before fusion begins?What two specific forms of equilibrium must be established for a star to officially land on the Zero-Age Main Sequence (ZAMS)?What external event is cited as a potential trigger for initiating gravitational collapse in a Giant Molecular Cloud (GMC)?What critical physical threshold must the density of a collapsing core cross to trap radiation and halt the initial free-fall phase?For stars similar to our Sun, what core temperature is required to ignite the proton-proton (P-P) chain reaction?What stellar objects result if a core never reaches the temperature needed for sustainable hydrogen fusion?According to the Virial Theorem, as gravity compresses a system, what energy component must increase to approach a new state of balance?What provides the powerful, outward-directed thermal pressure that finally counteracts the inward crush of gravity at fusion ignition?How does the timescale for gravitational collapse significantly differ for a high-mass protostar (e.g., $30 M_{ ext{sun}}$) compared to a Sun-like object?What ongoing process causes a stable main sequence star like the Sun to slowly evolve into a red giant later in its life?