What ultimate threshold must a protostar reach through compression to officially transition into a true star?
The core becomes hot and compressed enough for hydrogen nuclei to begin fusing into helium, releasing massive amounts of energy
The defining characteristic that separates a protostar, which glows only due to heat generated by gravitational squeeze, from a genuine, self-sustaining star lies in achieving controlled thermonuclear reactions. This transition point requires reaching extreme internal conditions—millions of degrees Celsius and immense pressures—which only deep, sustained compression of the nebular material can generate. Once the core achieves these thresholds, hydrogen nuclei begin fusing into helium, releasing enormous amounts of energy. This event, known as the start of nuclear fusion, officially marks the object's birth as a true star capable of powering itself independently.
