: Then why'd Lh'owon get destroyed?
Because it doesn't have a sun anymore. The trih xeem blew it up and the Jjaro station contained the explosion in a gravity field, basically making a black hole or at least a white dwarf star. The planet is still there, but it'll never see daylight again. It'll freeze over and die soon.
(Sidenote for those confused about black holes: the effects of a black hole the mass of our sun, where our sun it, would be non other than the change in radiation emitted by it. It wouldn't suck anything in any more than our sun does now. Same effect if Lh'owon's sun was made a black hole).