Scientists Have No Idea Why Betelgeuse Is Dimming

Betelgeuse is a star that is destined to go supernova at the end of its life. When that happens, the explosion will be bright. The catch is that the supernova isn't expected to occur for tens of thousands of years. Despite the supernova being thousands upon thousands of years away, the star is inexplicably getting dimmer. Scientists have no idea why.

Astronomers from Villanova University were first to report the dimming of the star. They did note that while the star is still dimming, the rate of dimming is slowing. Betelgeuse is a red supergiant star in the Orion constellation. It left the main sequence about a million years ago and has been a red supergiant for about 40,000 years.

Scientists say that Betelgeuse is a core-collapse SN II progenitor, which means eventually it will burn off enough hydrogen to collapse and will then explode as a supernova. It is a semi-regular variable star, meaning its brightness is variable. It has multiple cycles with one about 420 days long, and another of its cycles is about five to six years long. A third cycle is the shortest lasting 100 to 180 days.

The astronomers say that Betelgeuse's temperature has dropped by 100 Kelvin since September 2019, and its luminosity has declined nearly 25 percent in the same time frame. The star's radius is now about 9 percent larger, such swelling is expected as the star ages. Astronomers admit that there is a chance the dimming isn't from the star, but a cloud of gas and dust obscuring it.

The team also says that it is unknown if the dimming is directly related to the eventual supernova explosion. They are continuing to watch the star and report on it.