An artist’s impression of surprisingly persistent dust surrounding 49 Ceti, a star some 40 million years old.. Image: NAOJ
Astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) found a young star surrounded by an astonishing mass of gas. The star, called 49 Ceti, is 40 million years old and conventional theories of planet formation predict that the gas should have disappeared by that age. The enigmatically large amount of gas requests a reconsideration of our current understanding of planet formation.
Planets are formed in gaseous dusty disks called protoplanetary disks around young stars. Dust particles aggregate together to form Earth-like planets or to become the cores of more massive planets by collecting large amounts of gas from the disk to form Jupiter-like gaseous giant planets.
According to current theories, as time goes by the gas in the disk is either incorporated into planets or blown away by radiation pressure from the central star. In the end, the star is surrounded by planets and a disk of dusty debris. This dusty disk, called a debris disk, implies that the planet formation process is almost finished.
A composite ALMA image of debris surrounding 49 Ceti. Image: ALMA (ESO/NAOJ/NRAO), Higuchi et al.