Free Astronomy Magazine March-April 2018

34 MARCH-APRIL 2018 SPACE CHRONICLES Giant bubbles on red giant star’s surface by ESO L ocated 530 light- years from Earth in the constellation of Grus (The Crane), π 1 Gruis is a cool red giant. 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 be- come a similar red giant star in about five billion years. An international team of astronomers led by Claudia Paladini (ESO) used the PIONIER in- strument on ESO’s Very Large Telescope to ob- serve π 1 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 kilo- metres across — about a quarter of the star’s diameter. Granules are patterns of convection currents in the plasma of a star. As plasma heats up at the centre of the star it expands and rises to the sur- face, then cools at the outer edges, becoming darker and more dense, and descends back to the centre. This process continues for billions of T his colourful image shows the sky around the bright pair of stars π 1 Gruis (centre-right, very red) and π 2 Gruis (centre-left, bluish-white). Just right of centre the bright spiral galaxy IC 5201 is also visible and many other fainter galaxies are scattered across this wide-field image from the Digitized Sky Survey 2. [ESO/Digitized Sky Survey 2] years and plays a major role in many astrophysical processes including en- ergy transport, pulsation, stellar wind and dust clouds on brown dwarfs. Just one of these granules would extend from the Sun to be- yond Venus. The surfaces — known as photospheres — of many giant stars are obscured by dust, which hinders observations. However, in the case of π 1 Gruis, although dust is present far from the star, it does not have a significant effect on the new infrared observations.