page_title: AU Microscopii
section_title: Debris disk
hierarchical_section_title: AU Microscopii / Planetary system / Debris disk
caption_attribution_description: English: The top view, taken with NASA's Hubble Space Telescope, shows light reflected off dust in a debris disk around the young star AU Microscopii. The bottom frame labels features in this image, while the white lines on the disk indicate the light polarization direction. The image shows the flattened disk, appearing like Saturn's rings, but seen almost exactly edge-on. Normally, starlight would be so bright that the debris disk could not be seen. But astronomers used the coronagraph on Hubble's Advanced Camera for Surveys, which blocked out most of the starlight. The black circle in the center of the image is the coronagraph's occulting disk. The disk in this image extends to about 8 billion miles from the star, or three times farther than Neptune is from the Sun. In other observations, the disk has been traced to at least 11 billion miles.
context_page_description: AU Microscopii is a small star located 32.3 light-years away – about 8 times as far as the closest star after the Sun. The apparent visual magnitude of AU Microscopii is 8.73, which is too dim to be seen with the naked eye. It was given this designation because it is in the southern constellation Microscopium and is a variable star. Like β Pictoris, AU Microscopii has a circumstellar disk of dust known as a debris disk.
context_section_description: AU Microscopii harbors its own disk of dust, first resolved at optical wavelengths in 2003 by Paul Kalas and collaborators using the University of Hawaii 2.2-m telescope on Mauna Kea, Hawaii.  This large debris disk faces the earth edge-on, and measures at least 200 AU in radius.  At these large distances from the star, the lifetime of dust in the disk exceeds the age of AU Microscopii.  The disk has a gas to dust mass ratio of no more than 6:1, much lower than the usually assumed primordial value of 100:1.  The debris disk is therefore referred to as "gas-poor".  The total amount of dust visible in the disk is estimated to be at least a lunar mass, while the larger planetesimals from which the dust is produced are inferred to have at least six lunar masses.
  The spectral energy distribution of AU Microscopii's debris disk at submillimetre wavelengths indicate the presence of an inner hole in the disk extending to 17 AU, while scattered light images estimate the inner hole to be 12 AU in radius.  Combining the spectral energy distribution with the surface brightness profile yields a smaller estimate of the radius of the inner hole, 1 - 10 AU.
  The inner part of the disk is asymmetric and shows structure in the inner 40 AU.  The inner structure has been compared with that expected to be seen if the disk is influenced by larger bodies or has undergone recent planet formation.
  The surface brightness (brightness per area) of the disk in the near infrared  as a function of projected distance  from the star follows a characteristic shape.  The inner  of the disk appear approximately constant in density and the brightness is unchanging, more-or-less flat.  Around   the density and surface brightness begins to decrease: first it decreases slowly in proportion to distance as ; then outside , the density and brightness drops much more steeply, as .  This "broken power-law" shape is similar to the shape of the profile of β Pic's disk.
  In October 2015 it was reported that astronomers using the Very Large Telescope (VLT) had detected very unusual outward-moving features in the disk. By comparing the VLT images with those taken by the Hubble Space Telescope in 2010 and 2011 it was found that the wave-like structures are moving away from the star at speeds of up to 10 kilometers per second (22,000 miles per hour). The waves farther away from the star seem to be moving faster than those close to it, and at least three of the features are moving fast enough to escape the gravitational pull of the star.
caption: Hubble Space Telescope image of the debris disk around AU Microscopii.
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