S13 - Dispersal of the protoplanetary disk

Question 1

Describe the protostars transition to main sequence and prerequisites?

Answer 1

Starts when:
- Major accretion and outflows have ended. Surrounding envelope has faded.
- Remnant (debris) disk left around the young star.
As the star evolves:
- Inner region of the disk disappears
- Disk loses dust and becomes fainter
- Star becomes a cool black body (weak emitter).

Question 2

What is the mechanism responsible for dust removal from orbiting a star?

Answer 2

The Poynting-Robertson effect. Due to relativistic effects, the grain sees the photons from the star incident on it as acting at an angle creating a tangential retarding radiation pressure force against the orbital velocity of the dust grain.