First images: planet building blocks orbiting nearby star

For the first time, an image has revealed large dusty clumps near a young star that astronomers believe could gravitationally collapse to form giant planets.

The observations were announced by the European Southern Observatory (ESO) and used data from the ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA), both in Chile. The results are presented in a paper published in the Astrophysical Journal Letters.

Astrophysicists agree that dust and gas that forms around newly born stars develops into a “protoplanetary disc” which gradually condenses due to gravity to form planets.

Astronomers have captured pictures of “protoplanets” – planets in the making – around distant stars before. But catching a glimpse of the clumps that will eventually form baby planets has proven elusive, until now.

“This discovery is truly captivating as it marks the very first detection of clumps around a young star that have the potential to give rise to giant planets,” says co-author Alice Zurlo, an associate professor at Chile’s Universidad Diego Portales.

V960 Mon, the young star, is about 5,000 lightyears away and sits in the Monoceros constellation. It attracted astronomers’ attention in 2014 when its brightness suddenly increased more than 20 times.

Follow up observations made using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the VLT revealed material orbiting V960 Mon assembling into a series of spiral arms extending over an area greater than the size of our solar system.

VLT’s SPHERE gives astronomers insight into the dusty material around the star. Using archived data from ALMA, researchers were able to peer deeper into its structure.

“With ALMA, it became apparent that the spiral arms are undergoing fragmentation, resulting in the formation of clumps with masses akin to those of planets,” Zurlo explains.

Combining images from the two telescopes provided astronomers with a tantalising glimpse at giant planet formation around V960 Mon.

Two competing theories are put forward by astrophysicists to explain the formation of giant planets.

One hypothesis is that giant planets are created through “core accretion” – when dust grains come together slowly over time. The other, called “gravitational instability,” is when the slightly uneven distribution of material around the star leads to clumps forming, which collapse.

Evidence for “core accretion” has been found around stars before, but support for “gravitational instability” leading to planet formation has evaded astronomers. “No one had ever seen a real observation of gravitational instability happening at planetary scales until now,” says first author Philipp Weber from the University of Santiago, Chile.