T Tauri star

Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years.

There is evidence of large areas of starspot coverage, and they have intense and variable X-ray and radio emissions (approximately 1000 times that of the Sun).

Another source of brightness variability are clumps (protoplanets and planetesimals) in the disk surrounding T Tauri stars.

T Tauri stars generally increase their rotation rates as they age, through contraction and spin-up, as they conserve angular momentum.

The p-p chain for lithium burning is as follows It will not occur in stars with less than sixty times the mass of Jupiter (MJ).

A T Tauri stage for the Solar System would be one means by which the angular momentum of the contracting Sun was transferred to the protoplanetary disc and hence, eventually to the planets.