Astronomers find first evidence of a 'twisted' planet-forming disc

Astronomers find first evidence of a planet-forming disc that was torn apart by its three central stars – leaving it warped and with tilted rings

  • Researchers used multiple telescopes to discover the unusual planetary system
  • The trinary star system is named GW Orionis and is about 1,200 light years away
  • Observers on a planet in the system would see the three stars tilted to an angle 
  • Astronomers used shadows on the unusual disc to discover its twisted shape 

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 new observations revealed that this object has a warped planet-forming disc with a misaligned ring. In particular, the SPHERE image (right panel) allowed astronomers to see, for the first time, the shadow that this ring casts on the rest of the disc

Scattered light image of GW Orionis. 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.

Orange rings are the (misaligned) rings seen by ALMA. The transparent surfaces correspond to the lower-density dust filaments that connect the rings and that dominate the emission in scattered light

This is a snapshot from the computer simulation showing how the three stars on misaligned orbits shaped the disc around GW Orionis

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.’

ALMA images of the planet-forming disk with misaligned rings around triple star system GW Orionis

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.

THE VERY LARGE TELESCOPE IS A POWERFUL GROUND-BASED INSTRUMENT IN CHILE

The European Southern Observatory (ESO) built the most powerful telescope ever made in the Atacama Desert of northern Chile.

It is called the Very Large Telescope (VLT) and is widely regarded as one of the most advanced optical instruments ever made.

It consists of four telescopes, whose main mirrors measures 27 feet (8.2 metres) in diameter.

There are also four movable six feet (1.8 metre) diameter auxiliary telescopes.

The large telescopes are called Antu, Kueyen, Melipal and Yepun. 

The European Southern observatory (ESO) built the most powerful telescope ever made in the Atacama Desert of northern Chile and called it the Very Large Telescope (VLT).

The first of the Unit Telescopes, ‘Antu’, went into routine scientific operations on April 1, 1999.

The telescopes can work together to form a giant ‘interferometer’.

This interferometer allows images to be filtered for any unnecessary obscuring objects and, as a result, astronomers can see details up to 25 times finer than with the individual telescopes.  

It has been involved in spotting the first image of an extrasolar planet as well as tracking individual stars moving around the supermassive black hole at the centre of the Milky Way.

It also observed the afterglow of the furthest known Gamma Ray Burst, 

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