In the news this month... bubbles on Betelgeuse
An artist’s impression of the supergiant star Betelgeuse CREDIT: ESO/L. Calçada
Using state of the art techniques, two teams of astronomers have obtained the sharpest ever images of the supergiant star Betelgeuse. The second brightest star in the constellation of Orion, Betelgeuse appears red even to the naked eye, and is one of the largest stars known, almost 1000 times larger than the Sun. It is a type of star known as a red supergiant and is so enormous that if it were placed at the centre of the solar system, its surface would lie almost at the orbit of Jupiter. Stars this massive run out of fuel much quicker than smaller stars like the Sun, and eventually explode as supernovae.
There are still some unanswered questions about red supergiants, one of which is how they shed material. These stars can lose as much material as is contained in the entire Sun in just 10,000 years, but the mechanism by which this occurs is not well understood. But in work accepted for publication in the journal Astronomy and Astrophysics, two independent teams using ESO's VLT have made observations which might provide some answers.
The first team used adaptive optics which attempts to correct for the fluctuations in the Earth's atmosphere which make stars appear to twinkle. They combined this with another technique known as "lucky imaging" where only the sharpest exposures are combined to produce a high resolution image in a similar way to imaging with a webcam through a backyard telescope. The resulting images are so sharp that they could detect a tennis ball at the distance of the International Space Station. The team's images of Betelgeuse show a large plume of gas extending out from the star to more than six times the radius of the star itself, showing that it is not shedding material evenly in all directions.
Meanwhile, the other team used the VLT interferometer, which combines the light from three telescopes to produce results with much greater resolution. Using this technique, the second team were able to indirectly detect features up to four times smaller than the other teams images, allowing them to study the surface of Betelgeuse. They found that the gas in the star's atmosphere is moving up and down in giant bubbles like huge convections cells almost as large as the star itself. Together, these two superbly detailed observations suggest that it is these large scale motions in Betelgeuse's atmosphere which are responsible for producing the giant plumes of material.