Betelgeuse Update: Dimmest Magnitude Recorded In 125 Years

A Digitized Sky Survey 2 (DSS 2) image of Betelgeuse in brighter times. ESO/ Digitized Sky Survey 2/ Wikimedia Commons

Katy Pallister 31 Jan 2020, 15:09

Last week, the extreme dimming of the red supergiant knocked it out of the Top 20 brightest stars. However, there was worse news to come for the star as new data shows Betelgeuse has hit its dimmest point in 125 years, measuring just 37 percent of its usual brightness.

These latest measurements from the American Association of Variable Star Observers (AAVSO) adds to the past two months of observations that have documented this unprecedented dimming.


Betelgeuse can be found approximately 643 light-years away, on the shoulder of Orion, the Hunter. It weighs in at around 11 times the mass of our Sun, but has a radius almost 900 times greater (626 million kilometers/389 million miles). To put that into perspective, if the Sun were replaced with Betelgeuse, it would stretch to the orbit of Jupiter, completely engulfing the Earth.

According to data announced in The Astronomer’s Telegram, its radius has expanded by a further 9 percent since September 2019, whilst its luminosity has decreased by nearly 25 percent. Although its rate of dimming has seemed to decrease.

So what is the cause of the fainting Betelgeuse? Well, it still remains somewhat of a mystery to astronomers.

Periods of dimming and brightening are not uncommon for Betelgeuse as it is a semi-regular variable star. Its brightness oscillates in various cycle lengths; one lasting around 420 days, another for about five or six years, and a third shorter period of between 100 to 180 days.

Astronomers believe that the current dimming of Betelgeuse could just be an extra-strong version of the 420-day cycle. With the expected minimum of this period predicted to happen imminently, if Betelgeuse continues to dim, other explanations will have to be considered.

Betelgeuse’s brightness is not the only variable of the star. Images of its surface show it to be lumpy, behaving like an ever-changing blob. As its fuel is burnt up, the star’s mass decreases, weakening the gravitational hold on its outer edges. This enables gas and dust to be expelled, which could be what is currently obscuring our view of the star and causing the observed dimming.

Betelgeuse is also nearing the end of its life at 8.5 million years old, having left its main sequence phase (where our Sun is) about 1 million years ago. The inevitable outcome of the star will be a supernova, and some think that this dimming is an indicator that this huge explosion is around the corner.

One study has predicted the star’s remaining lifetime is 100,000 years, a “blink of an eye” by astronomical standards. Whilst Betelgeuse’s latest dimming period provides exciting observations and should be closely watched, expectations should be managed in regards to witnessing its explosive ending.

Yet that hasn’t stopped some people wishing on this old star.


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