Scientists have discovered that Deneb, one of the brightest stars in the night sky, shows significant changes in its light polarization. Over about 400 days starting in August 2022, Deneb's light polarization varied by several hundred parts per million (ppm) in an irregular way every few weeks. The biggest change was 2500 ppm, happening just after a known pulsation event.

Deneb is a type A2 Ia supergiant star and the 19th brightest in the night sky. It has been known to vary in brightness and speed, likely due to pulsations. Previous studies found that Deneb's variability is typical for such stars, but its exact behavior has been hard to pinpoint.

The new observations were made with high-precision instruments on various telescopes. These observations showed that Deneb's polarization changes on a timescale of weeks. The changes in polarization might be caused by density changes in Deneb's wind or extended atmosphere, or possibly due to its pulsations.

Scientists observed Deneb using advanced polarimeters and found that the changes in polarization are much larger than previously thought. This variability had been missed before because the changes were irregular and required high-precision instruments to detect.

The study suggests two possible reasons for the changes in polarization: clumpy winds and nonradial pulsations. Clumpy winds are common in stars like Deneb and can cause large variations in light polarization. Nonradial pulsations, which are distortions on the star’s surface, can also produce changes in polarization.

Future observations, combining polarimetry with spectroscopy and photometry, are needed to understand these changes better. These findings are crucial as they could help scientists learn more about the behavior and structure of supergiant stars like Deneb.