What phenomenon causes the initial rise in temperature and pressure within a collapsing protostar?

Answer

Conversion of gravitational potential energy into kinetic energy, which then thermalizes

As a gas cloud contracts under gravity, its gravitational potential energy is converted into the kinetic energy of the particles. Collisions among these particles cause this energy to thermalize, resulting in rising temperature and pressure.

What phenomenon causes the initial rise in temperature and pressure within a collapsing protostar?
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