ISB ~ Revelation 9 v1

a star fallen:A demon or fallen angel (8:10; 12:4, 9).

the bottomless pit:Or “the abyss”, which corresponds to the Hebrew Sheoland the Greek Hades. In the cosmology of Israel, this is the gloomy underworld where the spirits of men sink down after death to await the final Judgment (20:13; Ps 9:17; Wis 16:13-14). It is also the dwelling of infernal spirits that crawl up to bring death, destruction, and deception into the world of the living (11:7; 20:1-3; Lk 8:29-31; 2 Pet 2:4). Christ has authority over this realm because he holds the “keys” to the abyss and can order angels and demons to lock and unlock it at his discretion (1:18; 20:1).