Antares: astronomers capture best ever image of a star’s surface and atmosphere

Astronomers have produced the most detailed ever images of a star other than the sun.

The red supergiant, called Antares, is known as the heart of the Scorpius constellation because of its rosy hue, discernible to the naked eye, and location in the body of the astronomical beast. The new images, produced using the European Southern Observatory’s Very Large Telescope in Chile, are the most detailed yet of the surface and atmosphere of a star beyond our solar system.

The main picture, above, is constructed from images of Antares taken using ESO’s Very Large Telescope. This image is an artist’s impression of the red supergiant, based on the images and data captured.
 The main picture, top, is constructed from images of Antares taken using ESO’s Very Large Telescope. This picture is an artist’s impression of the red supergiant, based on the images and data captured. Illustration: M. Kornmesser/ESO/AFP/Getty Images

Antares, which is 550 light years from Earth, has a mass about 15 times that of the sun, but is rapidly losing material to surrounding space as it expands outwards in the last phase of its life before becoming a supernova. If Antares sat at the centre of our own solar system its outer layers would extend as far as Mars.

However, until now the exact process by which giant stars lose mass from their upper atmosphere has remained unknown.

This chart shows the prominent constellation of Scorpius. At the heart of this very striking grouping of stars lies Antares.
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 This chart shows the prominent constellation of Scorpius. At the heart of this very striking grouping of stars lies Antares. Illustration: IAU and Sky & Telescope/ESO

The latest images aim to tackle this question by mapping the motions of surface material in intricate detail using the Very Large Telescope Interferometer (VLTI).

The instrument combines the light from up to four telescopes to create a virtual telescope with a resolution equivalent to that of a single mirror up to 200 metres across.

Using the VLTI, astronomers have constructed this map of the motions of material on the surface of the star. In red regions the material is moving away from us and in the blue areas the material is approaching. The empty region around the star shows where velocity measurements were not possible.
 Using the VLTI, astronomers have constructed this map of the motions of material on the surface of the star. In red regions the material is moving away from us and in the blue areas the material is approaching. The empty region around the star shows where velocity measurements were not possible. Illustration: K. Ohnaka/ESO

“How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century,” said Keiichi Ohnaka, of the Universidad Católica del Norte, Chile, and the paper’s first author. “The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares – a crucial step towards clarifying this problem. The next challenge is to identify what’s driving the turbulent motions.”

The observations reveal unexpected turbulence – large clumps of upwelling and receding gas – in the star’s outer atmosphere. These movements could not be explained by convection currents, where the flow of gas transfers heat from the core to the outer limits of a star, pointing to the existence of new, currently unknown processes. The findings are published in the journal Nature.

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