Sher 25: A Pending Supernova . ... Sher 25, designated by the arrow, is a blue supergiant star located just outside the star cluster and emission nebula NGC 3603 . Sher 25 lies in the center of an hourglass shaped nebula much like the one that surrounds the last bright supernova visible from Earth: SN1987a . Now the hourglass shaped rings around SN1987a were emitted before that blue supergiant exploded. ... NASA Web Site Statements, Warnings, and Disclaimers . NASA Official: Jay Norris. ...