Astronomers have gained their sharpest ever view of a supergiant star that could be on the verge of exploding as a supernova. They zoomed in on red Betelgeuse in Orion to discover a giant bubble boiling on its surface and a huge plume of gas that is bigger than the solar system.
Two independent teams used the European Southern Observatory’s imaginatively named Very Large Telescope in Chile to study Betelgeuse close up. Their images provide new clues to explain how such enormous stars shed material at such a tremendous rate.
Betelgeuse lies 640 light-years away but is one of the brightest stars in the night sky. It is also one of the biggest and most luminous stars known, being nearly 1,000 times larger than the Sun and shining more than 100,000 times more brightly.
It is only a few million years old – a mere youngster compared to the four billion-year-old Sun – but is near the end of its life, astronomers believe. It seems doomed to blow itself to bits in a supernova blast that would make it brighter than the Moon and visible in broad daylight.
One team of scientists borrowed an old trick invented by amateur astronomers to get a clearer picture of Betelgeuse. Special so-called adaptive optics, using an instrument called NACO, helped compensate for distortion caused by the Earth’s atmosphere. But then they picked and combined just the sharpest images collected, discarding those made fuzzy by turbulence in the air.
The final picture with the 8-metre telescope was much sharper than a single long exposure could produce. Its resolution is so fine it could pick out an object the size of a tennis ball on the International Space Station as seen from the ground.
Pierre Kervella, of the Paris Observatory, who led the first team, said: “Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse. This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions.”
The plume extends to at least six times the diameter of Betelgeuse, corresponding to the distance between the Sun and Neptune. The star itself is so big that it would almost stretch out to the orbit of Jupiter if it was our sun.
Scientists needed to work out if the ejected material was being lost above the giant star’s polar regions due to its rotation or whether convection currents inside Betelgeuse were generating the plume.
To find out, a second team, led by Keiichi Ohnaka of the Max Planck Institute for Radio Astronomy in Bonn, Germany, used a technique called interferometry. The AMBER instrument on the Very Large Telescope Interferometer was used to combine the light from three separate 1.8-metre telescopes. This gave the team a picture as sharp as could be taken with one giant 48-metre telescope if it were possible to build such a monster and four times more detailed than the first team’s.
Ohnaka said: “Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse’s surface ― the first time this has been done for a star other than the Sun.”
These observations revealed that the gas in Betelgeuse’s atmosphere is moving vigorously up and down, and producing bubbles are as large as the supergiant star itself. It leads astronomers to believe that these movements of gas beneath Betelgeuse’s surface are behind the ejection of the massive plume into space.
Earlier this year, a team at Mount Wilson, California, suggested Betelgeuse was shrinking. The star was already known as the brightest variable star in the sky for amateurs to observe.
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