ALMA finds protoplanetary disks depicting planet formation

Washington  :  Astronomers have obtained stunning, high-resolution images of 20 nearby protoplanetary disks, depicting the birth of planets, using Chile's Atacama Large Millimeter/submillimeter Array (ALMA).

The observations are part of a major ALMA initiative known as the Disk Substructures at High Angular Resolution Project, or DSHARP campaign.

According to the researchers, the most compelling interpretation of these observations is that large planets, likely similar in size and composition to Neptune or Saturn, form quickly, much faster than current theory would allow. 

It may also help explain how smaller rocky planets manage to survive in the chaos of young systems.

"The goal of this months-long observing campaign was to search for structural commonalities and differences in protoplanetary disks. ALMA's remarkably sharp vision has revealed previously unseen structures and unexpectedly complex patterns," said Sean Andrews, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA). 

"We are seeing distinct details around a wide assortment of young stars of various masses. The most compelling interpretation of these highly diverse, small-scale features is that there are unseen planets interacting with the disk material," he added.

The results will appear in the Astrophysical Journal Letters.

Leading models for planet formation hold that planets are born by the gradual accumulation of dust and gas inside a protoplanetary disk, a process that takes many millions of years to unfold. This suggests that its impact on protoplanetary disks would be most prevalent in older, more mature systems. 

But ALMA's early observations of young protoplanetary disks, some only about one million years old, reveal surprisingly well-defined structures, including prominent rings and gaps, which appear to be the hallmarks of planets. 

"It was surprising to see possible signatures of planet formation in the very first high-resolution images of young disks. It was important to find out whether these were anomalies or if those signatures were common in disks," said Jane Huang, a graduate student at CfA.

The DSHARP campaign was designed to do precisely that by studying the relatively small-scale distribution of dust particles around 20 nearby protoplanetary disks. These dust particles naturally glow in millimeter-wavelength light, enabling ALMA to precisely map the density distribution of small, solid particles around young stars.