Yes, QUASAR is a Scrabble word!

Letter values in Scrabble US: Q 10, U 1, A 1, S 1, A 1, R 1.

Is it a valid word?

QUASAR is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a starlike object that may send out radio waves and other forms of energy; many have large red shifts

Also: quasi-stellar radio source.