During their death throes, as they are running out of fuel for the nuclear furnace in their cores, giant stars swell up to enormous size and eject huge amounts of gas and dust into space. But what drives out all that material? Radiation pressure is the main suspect, the idea being that photons from the star hit the dust grains, propelling them out into space. But typical grains of interstellar dust are just too small: At about a hundred-millionth of a meter, they just don’t catch enough photons. Now, a team using an instrument called SPHERE on the European Southern Observatory’s Very Large Telescope in Chile has found the answer. SPHERE was designed to directly observe planets around other stars, so it’s equipped with a mask to blot out the light from a star so that fainter things around it can be seen. The team used the instrument to observe the surroundings of the hypergiant star VY Canis Majoris (pictured) which is up to 40 times the mass of our sun and 300,000 times as luminous. As the researchers report this week in Astronomy & Astrophysics, they found that VY Canis Majoris is surrounded by dust grains 50 times larger than normal, giving them enough surface area to be successfully pushed away by the star’s radiation pressure. This explains how the dust ends up far out in space and, after the star has exploded as a supernova and dispersed more material, provides the seed material for a later generation of stars and planets.
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