Q:

Which event marks the birth of a star?

A:

Quick Answer

The final event that marks the birth of a star is bipolar flow. This is an eruption that releases two massive jets of gas that clear away gas and dust from the star’s surface.

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Full Answer

However, a gravity disturbance within a nebula, a cloud of interstellar dust and gas, is the event that initially begins the entire process. The disturbance might be caused by a comet, a shockwave from a distant explosion or some other event.

The force from the disturbance causes particles to collide and form clumps. As the clumps grow in mass and gravitational pull, they draw even more surrounding particles inward, which begin to rotate and flatten, forming a rotating disc.

As the speed of rotation increases, the disc pulls more material inward, creating a hot, dense core called a protostar. The process of drawing in gas and growing hotter continues until the protostar’s temperature is high enough to trigger the sustained nuclear fusion of its hydrogen atoms.

Though fusion produces an outflow of energy, material continues to flow inward until sufficient mass collapses to cause the bipolar flow. The young star then stabilizes and becomes a main sequence star whose outward pressure from hydrogen fusion is balanced with the inward pull of gravity.

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