Effective Pressures in Star Formation

The source of the energy for star formation is gravitational collapse - this collapse must provide enough energy to heat the gas of the protostar to the ignition point of hydrogen fusion, some 15 million Kelvins. This sounds relatively straightforward, but it is not simple freefall - the shrinking protostar encounters effective outward pressures which must be overcome.

• Gas pressure
• Radiation pressure

In the latter stages of the evolution of a star, the further collapses of stars toward white dwarf stars or neutron stars is impeded by other effective outward pressures:

• Electron degeneracy
• Neutron degeneracy

Gas Pressure in Stars

One component of the pressure in a star is the gas pressure or particle pressure. As the large mass of hydrogen and helium gas and dust (the protostar) begins to contract as a result of its gravitational forces, increased particle speed and collisions cause the average particle kinetic energy to increase. From the idea of kinetic temperature, it follows that there is an increased temperature and an associated pressure.

Starting the process of evaluating particle pressure with an ideal monoatomic gas, the Maxwell-Boltzmann velocity distribution can be used. The resulting expression for particle pressure is