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Gas guzzlers: Giant planet evolves as it feeds off young star

Astronomers have received an unprecedented glimpse into a key stage of birth for giant planets, courtesy of the world’s largest telescope, ALMA.

On Wednesday, ALMA (Atacama Large Millimeter/submillimeter Array) observed vast streams of gas flowing across a gap in the disc of material around a young star, according to a statement from the European Southern Observatory (ESO).

Such gas streams have been hypothesized to fuel the formation of giant planets, but until now have never been observed directly.

The ALMA array focused in over a distance of 450 light-years on the young star HD 142527, which is surrounded by a disc of gas and cosmic dust, left over from the star’s formation. Divided by a gap into an inner and outer disc, giant planets are thought to form by capturing streams of gas that bridge the gap.

“Astronomers have been predicting that these streams must exist, but this is the first time we’ve been able to see them directly,” says Simon Casassus leader of the new study. “Thanks to the new ALMA telescope, we’ve been able to get direct observations to illuminate current theories of how planets are formed!”

Consisting of 66 separate 12- and 7-meter radio telescopes arrayed across a 5,000-meter plateau in Chile’s Atacama desert, the ALMA is capable of observing submillimeter wavelengths of light. This makes it immune to light interference from the star’s glare that affects infrared or visible-light telescopes.

“We think that there is a giant planet hidden within, and causing, each of these streams,” says another team member, Sebastián Pérez. “The planets grow by capturing some of the gas from the outer disc, but they are really messy eaters: the rest of it overshoots and feeds into the inner disc around the star.”

Residual gas left in the gap between discs provides further evidence that the streams are caused by giant planet formation, and not drawn away by even larger bodies like a companion star. “A second star would have cleared out the gap more, leaving no residual gas,” Perez adds. “By studying the amount of gas left, we may be able to pin down the masses of the objects doing the clearing.”

The giant planets themselves proved elusive to the international team of scientists studying the system. “We searched for the planets themselves with state-of-the-art infrared instruments on other telescopes,” said Casassus. “However, we expect that these forming planets are still deeply embedded in the streams of gas, which are almost opaque. Therefore, there may be little chance of spotting the planets directly.”

Current limitations to ALMA’s observational power may change as the telescope nears completion and reaches its full capabilities. Even sharper vision will allow the team to determine properties of the planets themselves, such as mass, and give further clues to the mysteries surrounding planet formation.

The research was published this week in the journal Nature.