On Friday, January 4, 2019 at 1:43:16 PM UTC-8, Gerald Kelleher wrote:

Ultimately protoplanetary disks favor a transition phase involved in a supernova event rather than just the death of a star.

Completely incorrect and not even close to being the case. Utter Bull****, and note the capital "B".

Did you even read the description of that star, HL Tauri? Did you not note where it said "... the HL Tauri star system is only about one million years old"?

Sheesh!