The circumstellar environment of G29-38 first attracted attention in the late 1980s during a near-infrared survey of 200 white dwarfs conducted by
Ben Zuckerman and Eric Becklin to search for low mass companion stars and
brown dwarfs. G29-38 was shown to radiate substantial emission between 2 and 5 micrometres, far in
excess of that expected from extrapolation of the visual and near infrared spectrum of the star. Like other young, hot white dwarfs, G29-38 is thought to have formed relatively recently (600 million years ago) from its
AGB progenitor, and therefore the excess was naturally explained by emission from a
Jupiter-like brown dwarf with a temperature of 1,200
K and a radius of 0.15
solar radius. However, later observations, including
speckle interferometry, failed to detect a brown dwarf. Infrared observations made in 2004 by
NASA's
Spitzer Space Telescope indicated the presence of a dust cloud around G29-38, which may have been created by tidal disruption of an
exocomet or
exoasteroid passing close to the white dwarf. This may mean that G29-38 is still
orbited by a ring of surviving comets and, possibly,
outer planets. This is the first observation supporting the idea that
comets persist to the white dwarf stage of
stellar evolution. Infrared emission at 9-11 Mircons from
Spitzer spectroscopy were interpreted as a mixture of
amorphous olivine and a small amount of
fosterite in the disk. Modelling of the disk have shown that the inner edge of the disk lies at around 96±4 white dwarf radii and that the disk has a width of about 1-10 white dwarf radii. The dust mass of the disk is about 4-5 × 1018 g (about half the mass of a
massive asteroid) and the disk has a temperature less than 1000
K. The white dwarf is detected in
x-rays with
Chandra and
XMM-Newton. This is seen as evidence for
accretion from the disk and while the count number is small, there is evidence that this x-ray emission could come from
iron. == See also ==