First-Time Views of Solar System Births

by Anne Minard on February 17, 2011

SUBARU Telescope image of the protoplanetary disk around the young star LkCa 15. Credit: MPIA (C. Thalmann) & NAOJ

Chalk up a sizzling success for the HiCIAO planet-hunter camera on the Subaru Telescope in Hawaii: it’s captured this unprecedented image of a stellar disk similar in size to our own solar system, featuring rings and gaps that are associated with the formation of giant planets.

The lead image shows a bright arc of scattered light, in white, from the protoplanetary disk around the young star LkCa 15.  LkCa 15 is in the center of the image, blacked out. The arc’s sharp inner edge traces the outline of a wide gap in the disk. The gap is decidedly lopsided – it is markedly wider on the left side – and has most likely been carved out of the disk by one or more newborn planets that orbit the star.

The disk gap is large enough to house the orbits of all the planets in our own Solar System. “We haven’t detected the planets themselves yet,” said Christian Thalmann, who led the LkCa 15 study while on staff at the Max Planck Institute for Astronomy.”But that may change soon.”

LkCa 15, aged a few million years, is in the Taurus constellation about 450 light years away.

The observations are part of a systematic survey called SEEDS, or the Strategic Explorations of Exoplanets and Disks with Subaru Project, with a goal to search for planets and disks around young stars using HiCIAO, a state-of-the-art high-contrast camera designed specifically for this purpose. The lead investigator on the project is Motohide Tamura at the National Astronomical Observatory of Japan, but it’s a collaborative effort with international participation. Their first significant discovery — an exoplanet candidate around a sun-like star — was announced in December.

Besides LkCa 15, the researchers have also captured a sharp images of the protoplanetary disk around the very young star AB Aur in the constellation Auriga, “the Charioteer.” Lead researcher Jun Hashimoto, of the National Observatory of Japan, and his team report nested rings of material that are tilted with respect to the disk’s equatorial plane, and whose material, intriguingly, is not distributed symmetrically around the star – irregular features that indicate the presence of at least one very massive planet.

Recent images of AB Aur taken by HiCIAO (top left), compared with an image taken in 2004 by its predecessor instrument CIAO (top right). The new images give a much more detailed view of the inner regions (bottom left; with explanations bottom right): Intricate bright and dark patterns indicate the presence of different rings of matter. The fact that their centers do not coincide with the position of the star and the other irregularities point to the existence of a massive giant planet which is sweeping up the material between the rings. Credit: NAOJ/J. Hashimoto

The researchers point out that no other telescopes, whether ground-based or in space, have ever penetrated so close to a central star, showing the details of its disk.

Planetary systems like our own share a humble origin as mere by-products of star formation. A newborn star’s gravity gathers leftover gas and dust in a dense, flattened disk of matter orbiting the star. Clumps in the disk sweep up more and more material, until their own gravity becomes sufficiently strong to compress them into the dense bodies we know as planets.

Sources: Max Planck Institute For Astronomy, National Observatory of Japan.

Links to the published results:

Thalmann, C. et al., Imaging of a Transitional Disk Gap in Reflected Light: Indications of Planet Formation Around the Young Solar Analog LkCa 15 in Astrophysical Journal Letters 718, p. L87-L91

Hashimoto, J. et al., accepted for publication in Astrophysical Journal Letters in January 2011.

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