A Dwarf and Its Debris

IDL TIFF fileThis visible-light image of the debris disk around the red dwarf star AU Microscopii hints that planets may be forming or might already exist within it. The disk glows in light reflected by tiny grains of dust resulting from  the collisions of asteroids and comets. This debris disk is more than 40 billion miles across. The star at the center is quite young, about 12 million years old. It is only 32 light-years from Earth which makes its disk the closest yet seen in reflected starlight. It is also the first disk imaged around an M-type red dwarf, the most common type of star in the stellar neighborhood around the Sun.The disk has been cleared of dust within about a billion miles of the star. Images taken by Hubble (including this one) confirm that the disk is warped and has small variations in density that may have been caused by the tugging of an unseen companion, perhaps a large planet. That would be consistent with presence of the inner gap as well.

This debris disk is unusual in that it is the only one known that appears bluer than the star it surrounds. This possibly could it having a greater proportion of very small grains of dust  than other such disks. Smaller grains scatter blue light better than red. The surplus of small grains may be caused by the star not being bright enough to blow away tiny particles. Brighter, hotter stars would produce sufficient radiation to push small dust grains out of the disk and out into interstellar space

Image Credit: NASA

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