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Superstar spreads its wings

Nebula surrounding Betelgeuse

A nebula surrounds the red supergiant star Betelgeuse. The nebula forms as the behemoth sheds material into space. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen. Earlier observations of the heart of the nebula can be seen in the central disc.

ASTRONOMERS HAVE IMAGED a complex and bright nebula around the supergiant star Betelgeuse in greater detail than ever before. This structure, which resembles flames emanating from the star, is formed as the behemoth sheds its gas into space.

Betelgeuse, a red supergiant in the constellation Orion, is one of the brightest stars in the night sky. It is also one of the biggest, being almost the size of the orbit of Jupiter—about four and half times the diameter of the Earth’s orbit.

Hubble image of the surface of Betelgeuse

This image of Betelgeuse, released in 1996, was the first direct image of a star other than the Sun, and it was made with the Hubble Space Telescope. The image revealed a mysterious hot spot—more than ten times the diameter of Earth—on the stellar behemoth's surface.

The Very Large Telescope (VLT) image shows the surrounding nebula, which is much bigger than the supergiant itself, stretching 60 billion kilometres away from the star’s surface—about 400 times the distance of the Earth from the Sun.

Red supergiants like Betelgeuse represent one of the last stages in the life of a massive star. In this short-lived phase, the star increases in size, and expels gas into space at a tremendous rate—it sheds immense quantities of material (about the mass of the Sun) in just 10,000 years.

The process by which material is shed from a star like Betelgeuse involves two processes. The first is the formation of huge plumes of gas (although much smaller than the nebula now imaged) extending into space from the star’s surface.

The other, which is behind the ejection of the plumes, is the vigorous up and down movement of giant bubbles in Betelgeuse’s atmosphere—like boiling water circulating in a pot.

Raw material for new planets

Earlier images using an instrument called NACO, revealed the plumes close in to the star. The new results show that those plumes are probably connected to structures in the outer nebula now imaged at infrared wavelengths with a different instrument, VISIR.

The nebula cannot be seen at visible light wavelengths, as the glare of Betelgeuse completely outshines it.

The irregular shape of the nebula indicates that the star did not eject its material in a symmetric way. The bubbles of stellar material and the giant plumes they originate may be responsible for the clumpy look of the nebula.

The material visible in the new image is most likely made of silicate and alumina dust. This is the same material that forms most of the crust of the Earth and other rocky planets. At some time in the distant past, the silicates that eventually formed the Earth were expelled by a massive (and now extinct) star similar to Betelgeuse.

Adapted from information issued by ESO / P. Kervella / Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA.

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