ALMA discovers a never-before-seen star system cancer: what diet during treatment?


Astronomers have identified an early three-star system literally tearing its protoplanetary disc to shreds, leaving behind only distorted and misaligned rings.

Protoplanetary disks are the structures from which planets are formed around young stars. Over time, matter begins to clump together and eventually mold protoplanets and other minor bodies.

In one-star star systems like our Solar System, planets and rock belts more or less line up along a flat plane, circling the star’s equator. In contrast, this is not necessarily the case with multiple star systems. Located about 1300 light years from Earth, the GW Orionis system is the perfect example.

A one-of-a-kind system

This system consists of three stars. The first two revolve around each other every 241 days at a distance of about one astronomical unit. As a reminder, one AU is equivalent to the average distance between the Earth and the Sun. The third star moves around the pair every eleven and a half years in a misaligned orbit at a distance of eight AU.

Using ESO’s Very Large Telescope (VLT) and Atacama’s Large Millimeter / Submillimeter Antenna Array (ALMA) in Chile, astronomers were able to probe the unique geometry of this system. Around the three stars, the protoplanetary cloud breaks up into three rings at distances of 46, 185 and 340 astronomical units from the center of the system.

The outer ring is incidentally the largest ever observed in a protoplanetary system. For comparison, Pluto’s average distance from the Sun is 39.5 astronomical units.

In this configuration, the inner ring is completely misaligned with respect to the other two. The new research also reveals that this inner ring contains enough material to form multiple worlds. All future planets formed in this misaligned ring will then move around the star in very oblique orbits.

A hidden planet?

Direct observations combined with computer simulations have made it possible to understand that these protoplanetary misalignments are mainly the work of the conflicting gravitational pull of the three stars involved in different planes. However, according to the researchers, this is not the only factor at play. The presence of a planet between these rings is also, according to them, necessary to explain this amazing configuration.

“This planet probably carved out a dust space and broke the disc at the location of the present inner and outer rings,” suggests astronomer Nienke Van der Marel of the University of Victoria. If such a planet does exist, it would be the first ever isolated around three stars. Future observations of this fascinating system will confirm (or not) the discovery.