Betelgeuse, the red supergiant in Orion, has been growing fainter in recent months. The star's changing brightness stems from three overlapping causes: its regular 430-day pulsation cycle, a mysterious 2,100-day dimming cycle, and dust eruptions from its surface.
The 430-day cycle operates like a heartbeat. When Betelgeuse expands, its outer layers cool and it dims. When it contracts, they heat up and it brightens. At maximum, the star shines with the luminosity of about 14,000 suns. At minimum, about 7,600 suns. Located 650 light-years away, Betelgeuse ranks among the largest and most luminous red supergiants known.
The longer 2,100-day dimming cycle remained unexplained for a century until January 2026. Researchers using the European Southern Observatory's Very Large Telescope and NASA's Hubble Space Telescope published direct evidence of a faint companion star orbiting Betelgeuse. The companion, formally named Alpha Ori B and given the Arabic name Siwarha (meaning "her bracelet"), orbits deep within Betelgeuse's outer chromosphere every six years. As Siwarha moves through ejected gas and dust, its gravity creates a dense wake. When this concentrated dust trail passes between Earth and Betelgeuse, it dims the main star.
The dramatic Great Dimming of 2019 to 2020 revealed the third factor. Between October 2019 and February 2020, Betelgeuse lost over two-thirds of its brightness, falling from magnitude +0.5 to +1.7. Data from Hubble and ground observatories showed that a massive bubble of superhot plasma erupted from inside the star and blasted into space. The ejected gas cooled and condensed into silicon monoxide dust, which blocked starlight like a screen. This eruption coincided with the lowest point of the star's 430-day pulsation cycle and orbital interference from Siwarha, creating what researchers describe as a "perfect storm" of maximum dimming.
Since August, Betelgeuse has faded from magnitude +0.5 to +0.95, now appearing slightly dimmer than Aldebaran in Taurus. The current decline may reflect another episode of the 2,100-day dimming cycle, though the brightness change alone does not establish its cause.