Yuko kakazu uses subaru Telescope to search for collections of stars, planets, gas, and dust called

Galaxies.

Explanation:

A galaxy is a massive gravitational star system.  They contain stars and their remains. Planets and other celestial bodies can orbit the stars. Between the stars is an interstellar substance containing gas, cosmic dust, and cosmic radiation, the denser regions of which are interstellar clouds. In addition, galaxies contain large amounts of dark matter, the nature of which is unknown.

Whereas for a long time the number of galaxies in the visible universe was long estimated at 200 billion, the number of galaxies is estimated to be at least 2 trillion based on recent observations.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.