Red giant star Betelgeuse is shrinking

Orion’s red supergiant Betelgeuse has been steadily shrinking over the last 15 years.

Betelgeuse is so big that if placed in our Solar System it would extend to the orbit of Jupiter. But thanks to long term monitoring by Berkeley’s Infrared Spatial Interferometer (ISI) at Mt Wilson, measurements of the star’s diameter reveal the giant to be shrinking. Over the last 15 years, the star has shrunk by more than 15 percent, equivalent to the same diameter as the orbit of Venus.

Despite its diminished size however, there is no evidence to suggest that the star is dimming. But we do not know why the star is shrinking.

Since the star’s size depends on the wavelength of light used to measure it, it is difficult to compare measurements. Tenuous gas in the outer regions of the star emits light as well as absorbs it, which presents a challenge in determining the edge of the star.