<Tr> <Th> Theoretical concepts </Th> </Tr> <Tr> <Td> Accretion Initial mass function Jeans instability Kelvin--Helmholtz mechanism Nebular hypothesis Planetary migration </Td> </Tr> <Tr> <Td> Star portal </Td> </Tr> <Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr>

Why is hydrogen burning the main energy source for main-sequence stars