T Tauri Stars
The path a protostar takes to becoming a main sequence star is interrupted by it first becoming a T Tauri star. A protostar stage continues as long as material is still falling inward. After about 100,000 years or so, the protostar stops growing and the disk of material surrounding it is blown away by destroyed by radiation. It then becomes a T Tauri star, and is visible to Earth-based telescopes.
This is a very young, lightweight star, with an age less than 10 million years old and has an accumulated mass that is less than 3 solar masses. It is still undergoing gravitational contraction building up pressure and temperature but it represents an intermediate stage between a protostar and a low-mass main sequence star like the Sun.
When enough mass has accumulated, the process of fusion begins and a struggle for equilibrium starts. The nuclear fusion causes the atoms to radiate heat and light, creating pressure directed outward, but the increased mass, increases the pull of gravity, which causes the star to collapse, an inward process.
It is the balance of these inward and outward forces that results in equilibrium. If a point of critical mass is not reached the protostar becomes a brown dwarf. But if critical mass is reached, the protostar becomes a star and it moves into the main sequence.
The nearest T Tauri stars can be located in the Taurus molecular cloud and the Rho Ophiuchus Cloud. They are not close by: both are located nearly 460 light-years away. The name T Tauri comes from the first object recognized in the Taurus constellation with these properties.