Star
noun, の adjective
A constant star is the kind that stays in one place. It's just a regular star, like the north star or our sun, not a comet or an asteroid.
こうせい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
ブラックホールが、恒星をばらばらに引き裂くことがあるらしい。
Apparently, there are times the black hole tears stars into pieces.