Astronomers say they have witnessed a planet being born from a disk of gas and dust swirling around a young star, with an even more controversial conclusion: that this planet is forming from gas that is collapsing under its own gravity.
Astronomers say they have witnessed a planet being born from a disk of gas and dust swirling around a young star. Such claims have been made before, but the team comes to an even more controversial conclusion: that this planet is forming from gas that is collapsing under its own gravity, a mechanism known as gravitational or disk instability.
Although more than 5000 exoplanets have been discovered, only a few tens have been imaged directly, and none in the act of being born. Currie and colleagues were intrigued by the nearby star AB Aurigae because it was young—somewhere between 1 million and 4 million years old—and because its disk contains kinked, spiral features that could indicate protoplanets. But showing that some of the light from its disk was from a glowing-hot new planet rather than reflected starlight was no easy task.
Others are not entirely convinced there is a planet in there. “Direct imaging is a very subtle game,” says Roman Rafikov of the University of Cambridge, and the elaborate data processing required can make images deceptive. He adds it’s concerning that two other giant optical telescopes, Europe’s Very Large Telescope in Chile and the Large Binocular Telescope Observatory in Arizona, see nothing at the location.
At long distances from a star, however, simulations suggest planetesimal collisions are rare, so it would take too long to build up a planetary core; winds from the newborn star would blow away the disk gas before the core could scoop it up. To explain how planets like Jupiter can get around this, theorists including Johansen and others came up with pebble accretion.