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takyon [soylentnews.org] writes:

Astronomers have used the European Southern Observatory's Very Large Telescope to observe giant "bubbles" [eso.org] (granulation cells/patterns) extending from the surface of the red giant π¹ Gruis (aka Pi1 Gruis):

Astronomers using ESO's Very Large Telescope have for the first time directly observed granulation patterns on the surface of a star outside the Solar System — the ageing red giant π¹ Gruis. This remarkable new image from the PIONIER instrument reveals the convective cells that make up the surface of this huge star, which has 350 times the diameter of the Sun. Each cell covers more than a quarter of the star's diameter and measures about 120 million kilometres across. These new results are being published this week in the journal Nature.

Located 530 light-years from Earth in the constellation of Grus [wikipedia.org] (The Crane), π¹ Gruis [wikipedia.org] is a cool red giant [wikipedia.org]. It has about the same mass as our Sun, but is 350 times larger and several thousand times as bright. Our Sun will swell to become a similar red giant star in about five billion years.

An international team of astronomers led by Claudia Paladini (ESO) used the PIONIER [eso.org] instrument on ESO's Very Large Telescope [eso.org] to observe π¹ Gruis in greater detail than ever before. They found that the surface of this red giant has just a few convective cells, or granules, that are each about 120 million kilometres across — about a quarter of the star's diameter. Just one of these granules would extend from the Sun to beyond Venus. The surfaces — known as photospheres [wikipedia.org] — of many giant stars are obscured by dust, which hinders observations. However, in the case of π¹ Gruis, although dust is present far from the star, it does not have a significant effect on the new infrared observations.

Also at EarthSky [earthsky.org].

Large granulation cells on the surface of the giant star π¹ Gruis [nature.com] (DOI: 10.1038/nature25001) (DX [doi.org])

Open access version of the above paper: Convective pattern on the surface of the giant star π¹ Gruis [eso.org]

Related: Very Large Telescope Interferometer Captures Best Ever Image of Another Star (Antares) [soylentnews.org]
ALMA Captures Best-Ever Image of Red Giant W Hydrae [soylentnews.org]

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