Astronomers find first evidence of a ‘twisted’ planet-forming disc

Astronomers have discovered a strange young star system 1,200 light years from Earth where the planet-forming disc had been ripped apart by its three central stars.

This is the first direct evidence that groups of stars can tear apart the disc of dust and gas that goes on to form worlds – leaving it with warped and tilted rings.

Experts from the University of Exeter used a number of instruments including the European Southern Observatory’s Very Large Telescope to make the discovery.

Our Solar System is remarkably flat, with the planets all orbiting in the same plane – but that isn’t always the case and in this system they would be tilted to an angle.

Standing on a potential planet inside the system named GW Orionis would give the observer a stunning view of a tilted, multiple star system, astronomers claim.

The research came out of a large programme looking at young stellar systems using a new infrared imager combining light from six different telescopes.

The instrument has been designed to give new insights into how star and planet formation is taking place within the rotating, discs surrounding young stars.

Young planetary systems formed around multiple stars – such as GW Orionis – can form with broken-apart, deformed and twisted planet-forming discs. 

Stefan Kraus, professor of astrophysics at the University of Exeter, who led the research said this was the sharpest view yet of the intriguing system.

He described the three stars at the centre of the unusually twisted disc as being in a type of ‘gravitational dance’.

‘Normally, planets form around a flat disc of swirling dust and gas – yet our images reveal an extreme case where the disc is not flat at all,’ said said Kraus,

Instead it is warped and has a misaligned ring that has broken away from the disc – the misaligned ring is near the inner part of the disc close to the three stars. 

‘The effect is that the view of a potential planet within this ring looks remarkably like that of Tatooine, of Star Wars fame.’

The team were able to image the inner ring and confirm its misalignment using the SPHERE instrument on VLT and observations from the ALMA telescopes. 

The team observed shadows that this ring casts on the rest of the disc which helped them figure out the 3D shape of the rings and overall disc geometry.

The new research reveals that this inner ring contains 30 Earth masses of dust, which could be enough to form planets.

Alexander Kreplin of the University of Exeter, said any planets that form within the misaligned ring will orbit the star on a highly oblique orbit.

‘We predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging surveys’ of this system, Kreplin said.

‘Since more than half of stars in the sky are born with one or more companions, this raises an exciting prospect: there could be an unknown population of exoplanets that orbit their stars on very inclined and distant orbits.’

To reach these conclusions, the team observed GW Orionis for over 11 years and mapped the orbit of the stars with unprecedented precision. 

Alison Young, a member of the team from the Universities of Exeter and Leicester, said: ‘We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc.’

The international team, with researchers from the UK, Belgium, Chile, France and the US, then combined their exhaustive observations with computer simulations to understand what had happened to the system. 

For the first time, they were able to clearly link the observed misalignments to the theoretical ‘disc-tearing effect’, which suggests that the conflicting gravitational pull of stars in different planes can warp and break their surrounding disc.

‘We conducted simulations that show that the misalignment in the orbits of the three stars could cause the disc around them to break into distinct rings. This is what we see in the observations.’, said Matthew Bate, professor of theoretical astrophysics at Exeter, who carried out some of the computer simulations on the system. 

‘The observed shape of the inner ring also matches predictions on how the disc would tear.’

The research was presented in the journal Science.