Stars on the Verge: Analyses of the Complex Light Variations of the Hyper-luminous Red Supergiant VY Canis Majoris: On the Nature of the Star’s “Great Dimming” Episodes

Abstract

Abstract VY Canis Majoris (VY CMa) is one of the largest, most luminous red supergiant (RSG) stars in the Galaxy. This huge oxygen-rich RSG may be on the verge of becoming a bright core-collapse Type-II supernova. Over the 20th century, VY CMa has been undergoing episodic large quasi-periodic light variations. It has experienced two “great dimming” episodes during ∼1920–1950 and ∼1985–1995. During these, the star underwent large (1–2.5 mag) quasi-periodic light variations with dominant periods ranging between ∼1415 and 1565 days. In addition to experiencing large quasi-periodic light variations, VY CMa became fainter by 1.0–1.5 mag during the 1920–1950 episode. There is evidence that the star’s brightness decreased from ∼6.5–7.0 to ∼8.0–8.5 mag from 1850 to after 1900. These long-term dimming events may arise from dust formation from previously expelled gas. The light variations and the “dimmings” of VY CMa far surpass the recent “great dimming” of Betelgeuse.