The unexpected dimming of star Betelgeuse mystified astronomers who feared it would mean an end to the red supergiant, but a new discovery put this claim to rest.
NASA’s Hubble Space Telescope reveals the dimming was likely due to a traumatic outburst that ejected hot material into space.
Data shows a dust cloud formed when the superhot plasma was ejected from the star, cooled and formed a dust cloud that blocked light from its surface.
The mysterious change started in October 2019 and a year later Betelgeuse had returned to its normal brightness, suggesting the dark cloud finally disappeared into space.
The red supergiant star is about 700 light-years away from Earth and astronomers noticed it was getting dimmer late last year – a possible sign it was going to explode.
A supernova occurs when a giant star reaches the end of its life and runs out of fuel – it condenses in on its self then expels its material in a giant explosion.
However, Hubble has shown that all is well -for the time being.
Andrea Dupree, associate director of the Center for Astrophysics at Harvard & Smithsonian, said: ‘With Hubble, we see the material as it left the star’s visible surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim.’
‘We could see the effect of a dense, hot region in the southeast part of the star moving outward.’
Dupree and her team began using Hubble last year to probe Betelgeuse, following claims it was dimming and may soon explode.
The ultraviolet-light sensitivity capabilities of the telescope allowed researchers to see through the layers above the star’s surface – a region that clocks in at more than 20,000 degrees Fahrenheit.
These layers are heated partly by the star’s turbulent convection cells bubbling up to the surface and cannot be detect at visible wavelengths.
Hubble found magnesium was moving about 200,000 miles per hour as it passed from the surface to the outer atmosphere.
Dupree and her team believe the material shot beyond Betelgeuse’s visible atmosphere – some millions of miles away.
Being this deep into space caused a cooling effect, resulting in the dark cloud that shrouded part of the star’s surface.
‘This material was two to four times more luminous than the star’s normal brightness,’ said Dupree.
‘And then, about a month later, the south part of Betelgeuse dimmed conspicuously as the star grew fainter.’
‘We think it is possible that a dark cloud resulted from the outflow that Hubble detected.
‘Only Hubble gives us this evidence that led up to the dimming.’
The star is relatively nearby, about 725 light-years away, which means the dimming would have happened around the year 1300.
But its light is just reaching Earth now.
‘No one knows what a star does right before it goes supernova, because it’s never been observed,’ Dupree explained.
‘Astronomers have sampled stars maybe a year ahead of them going supernova, but not within days or weeks before it happened. But the chance of the star going supernova anytime soon is pretty small.’