Astronomers using ESO’s Very Large Telescope Interferometer (VLTI) have discovered exozodiacal light – starlight reflected from dust created as the result of collisions between asteroids and the evaporation of comets – close to the habitable zones around nine nearby stars.
This artist’s view from an imagined planet around a nearby star shows the brilliant glow of exozodiacal light extending up into the sky and swamping the Milky Way. Image credit: ESO / L. Calçada.
From dark clear sites on our planet, zodiacal light looks like a faint diffuse white glow seen in the night sky after the end of twilight, or before dawn. It is created by sunlight reflected off tiny particles and appears to extend up from the vicinity of the Sun.
This reflected light is not just observed from Earth but can be observed from everywhere in the Solar System.
The glow being observed by a team of astronomers led by Dr Steve Ertel of the University of Grenoble in France is a much more extreme version of the same phenomenon.
Using the VLTI in near-infrared light, the astronomers observed 92 nearby stars to probe exozodiacal light from hot dust close to their habitable zones. And they discovered bright zodiacal light glowing around nine of them – HD 2262, HD 7788, HD 14412, HD 20794, HD 28355, HD 39060, HD 104731, HD 108767 and HD 210302.
Where the exozodiacal light was present they were able to fully resolve the extended discs of dust, and separate their faint glow from the dominant light of the star.
“The exozodiacal light detected around these stars is a factor of 1,000 times brighter than the zodiacal light seen around the Sun,” Dr Ertel and his colleagues said.
“The high detection rate found at this bright level suggests that there must be a significant number of systems containing fainter dust, undetectable in our survey, but still much brighter than the Solar System’s zodiacal dust,” added Dr Olivier Absil of the University of Liège in France, who is a co-author of a paper published in the journal Astronomy & Astrophysics (arXiv.org preprint).
By analyzing the properties of the stars, they found that most of the dust was detected around older stars.
The astronomers explained: “this result was very surprising and raises some questions for our understanding of planetary systems. Any known dust production caused by collisions of planetesimals should diminish over time, as the number of planetesimals is reduced as they are destroyed.”
The sample of observed objects also included 14 stars for which the detection of exoplanets has been reported.
All of these planets are in the same region of the system as the dust in the systems showing exozodiacal light.
“Exozodiacal dust emission, even at low levels, makes it significantly harder to detect Earth-like planets with direct imaging,” the scientists said.
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S. Ertel et al. 2014. A near-infrared interferometric survey of debris-disk stars IV. An unbiased sample of 92 southern stars observed in H band with VLTI/PIONIER. A&A 570, A128; doi: 10.1051/0004-6361/201424438
