What particularly causes the T Tauri star to eject the strong bipolar wind which clears the gases around the star?
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$\begingroup$ Bipolar outflows are usually characteristic of younger stars than T Tauri type. Are you asking about Herbig–Haro objects or younger than T Tauri type stellar wind bow shock? $\endgroup$– TildalWaveCommented Dec 6, 2013 at 6:55
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$\begingroup$ i wanna ask about the kind of wind that cleared up the gas cloud in our solar system in its early years. $\endgroup$– ShivamCommented Dec 6, 2013 at 15:28
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1 Answer
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If you want to trigger outflows, there are two main processes that can help:
- magnetic field;
- radiation pressure.
Magnetic fields is well-suited to launch such outflows, through magneto-centrifugal effects. Basically, if there is magnetic fields tighed to the disk surrounding the protostar and the angle between the field lines and the disk is right, a particle from the disk that follows the magnetic field lines can be ejected. This is the well-known Blandford & Payne (1982) mechanism.
Note that, at earlier stages of star formation, magnetic field could also trigger outflows by a "magnetic field tower" growth. Basically, during the collapse of the prestellar core into a protostar, the field lines are dragged and twisted (due to the rotation of the core), the twist propagating from the inner to the outer region of the core, that triggers outflows. This kind of thing is discussedd in Hennebelle & Fromang (2008).
By the way, these two mechanisms are complementary, because slow outflows (of the order of 10 km s$^{-1}$) are observed around young protostar, whereas "fast outflows" -- jets, of the order of 100 km s$^{-1}$ -- are observed around late protostars, and these two mechanisms explained well the former and the later.
For more massive stars, radiation pressure will plays a role in outflows triggering. The protostar radiates away a part of its accreting energy, and strong a radiation pressure can trigger the growth of a kind of "bubble", that is an outflow (you can see Hennebelle & Commerçon (2012) for a brief review of the question).
Regarding your comment on your own question, it is mostly radiation pressure that will clear up the gas around the new-born star, that is clearly not an outflow or anything alike.
