July 2015
Valerie Rapson
First Likely Planets in a Nearby
Circumbinary Disk
Gemini Planet Imager (GPI) observations of V4046 Sagittarii
provide the first strong evidence for ongoing planet formation
around a young nearby binary star with a circumbinary disk.
The GPI data reveal a distinct double ring structure within the
disk that roughly corresponds to the orbital positions of Uranus
and Saturn in our own Solar Syste m. The discovery provides tests
of giant planet formation theories.
Stars form when a region within a giant molecular cloud, composed mostly of hydrogen
gas but including more complex molecules and dust, begins to gravitationally collapse. As
it does so, individual clumps start to spin up and flatten out, creating young protostars surrounded by disks of gas and dust. It’s within these circumstellar disks that planets, like those
in our Solar System, will form.
To better understand how planets form, we can study the nearest young stars known to host
planet-forming disks. The proximity of these star-disk systems allows astronomers to more
easily image the disks and search for evidence of planet formation. In the not-too-distant
future, we may even begin to directly image the newborn planets themselves.
Planet Formation Around Nearby Young Stars
Planet-forming circumstellar (protoplanetary) disks have been observed to extend out to radii of a few hundred astronomical units (AU) and are composed of a vast array of molecules,
including diatomic hydrogen (H2), carbon monoxide (CO), water (H2O), and various carbonbearing compounds found in our Solar System — such as hydrogen cyanide (HCN), cyanide
(CN), and ethynide (C2H). Protoplanetary disks also contain carbonaceous and silicate dust
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GeminiFocus
2015 Year in Review
January 2016