Astronomers see signs of planet birth

Astronomers have reported what could be the first direct evidence of a baby planet coming into existence.

Around the young star AB Aurigae lies a dense disc of dust and gas in which the ESO’s Very Large Telescope (VLT) has spotted a prominent spiral structure with a twist that marks the site where a planet may be forming. 

“Thousands of exoplanets have been identified so far, but little is known about how they form,” says Anthony Boccaletti from the Observatoire de Paris, France, lead author of a paper in the journal Astronomy & Astrophysics. 

AB Aurigae is 520 light-years from Earth in the constellation of Auriga (The Charioteer). The twist lies at about the same distance from the star as Neptune is from the Sun.

The new images showcase a spiral of dust and gas around the star. Spirals of this type signal the presence of baby planets, which “kick” the gas, creating “disturbances in the disc in the form of a wave, somewhat like the wake of a boat on a lake”, says Emmanuel Di Folco, from the Astrophysics Laboratory of Bordeaux (LAB), France.

As the planet rotates around the central star, this wave gets shaped into a spiral arm. The very bright yellow twist region close to the centre of the new image is one of these disturbance sites where the team believe a planet is being made.

Previous observations by the Atacama Large Millimeter/submillimeter Array (ALMA) provided the first hints of ongoing planet formation around AB Aurigae: scientists spotted two spiral arms of gas close to the star, lying within the disc’s inner region. 

In the new images, Boccaletti and a team of astronomers from France, Taiwan, the US and Belgium observed the fainter light from small dust grains and emissions coming from the inner disc. They confirmed the presence of the spiral arms – and noticed the twist.

“The twist is expected from some theoretical models of planet formation,” says LAB’s Anne Dutrey. “It corresponds to the connection of two spirals – one winding inwards of the planet’s orbit, the other expanding outwards – which join at the planet location. They allow gas and dust from the disc to accrete onto the forming planet and make it grow.”

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