Planet formation around binary star examined

Astronomers have taken a new, detailed look at the very early stages of planet formation around a binary star about 450 light-years from Earth.
Embedded in the outer reaches of a double star's protoplanetary disk, researchers discovered a striking crescent-shape region of dust that is conspicuously devoid of gas.
Using the Atacama Large Millimetre/submillimetre Array (ALMA), astronomers took a new, detailed look at the planet-forming disk around HD 142527, a binary star about 450 light-years from Earth in a cluster of young stars known as the Scorpius-Centaurus Association.
The HD 142527 system consists of a main star a little more than twice the mass of the Sun and a smaller companion star only about a third the mass of the Sun.

They are separated by approximately one billion miles - a little more than the distance from the Sun to Saturn.
"This binary system has long been known to harbour a planet-forming corona of dust and gas," said Andrea Isella from Rice University in Texas.

"The new ALMA images reveal previously unseen details about the physical processes that regulate the formation of planets around this and perhaps many other binary systems," Isella said.
Planets form out of the expansive disks of dust and gas that surround young stars. Small dust grains and pockets of gas eventually come together under gravity, forming larger and larger agglomerations and eventually asteroids and planets.

ALMA's new, high-resolution images of HD 142527 show a broad elliptical ring around the double star. The disk begins incredibly far from the central star - about 50 times the Sun-Earth distance.
Most of it consists of gases, including two forms of carbon monoxide (13CO and C180), but there is a noticeable dearth of gases within a huge arc of dust that extends nearly a third of the way around the star system.
This crescent-shaped dust cloud may be the result of gravitational forces unique to binary stars and may also be the key to the formation of planets, researchers suggest.

Its lack of free-floating gases is likely the result of them freezing out and forming a thin layer of ice on the dust grains, they said.
"The temperature is so low that the gas turns into ice and sticks to the grains. This process is thought to increase the capacity for dust grains to stick together, making it a strong catalyst for the formation of planetesimals, and, down the line, of planets," said Isella.