How was the dense, equatorial ring surrounding the progenitor of SN 1987A likely formed?

Answer

From stellar winds blowing off the star during previous evolutionary phases.

Observations revealed that the surrounding material existed as a dense, equatorial ring orbiting the star before the explosion, a structure likely formed by stellar winds during the star's earlier life stages.

How was the dense, equatorial ring surrounding the progenitor of SN 1987A likely formed?
starsexpansionastrophysicssupernova remnantsshock waves