Sher 25: A Pending Supernova? ... Sher 25, designated by the arrow, is a blue supergiant star located just outside the open star cluster and ionized region named 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 . ... Maybe Sher 25 has expelled these bipolar rings in a step that closely precedes a supernova . Maybe not. ... NASA Web Site Statements, Warnings, and Disclaimers . ...