How does hydrogen fusion begin in a protostar?

Hydrogen fusion in a protostar begins primarily through the gravitational attraction of particles. As the protostar forms, gravity causes the gas and dust in the surrounding molecular cloud to collapse inward. This process increases the density and temperature of the material at the center of the protostar.

As the particles come closer together under their own gravitational pull, the kinetic energy from their motion increases, leading to extremely high temperatures—typically in the range of millions of degrees Celsius. These temperatures are essential for overcoming the repulsive forces between hydrogen nuclei, allowing them to collide with enough energy to fuse and form helium.

This initiates the process of nuclear fusion, which is the primary source of energy for stars, allowing them to shine and eventually leading to the formation of stable stars. Once hydrogen fusion begins, it leads to a significant release of energy, which further stabilizes the star and supports it against gravitational collapse.

The other options do not accurately describe the primary mechanism for starting hydrogen fusion in a protostar. External gas pressure alone does not initiate fusion; rather, it's the internal conditions created by gravitational attraction that play a crucial role. Temperature variations may occur, but they are a result of gravitational contraction, not an independent mechanism. Radiation from surrounding stars is also