A fascinating constellation in their sights: Astronomers report on a trio of stars that tore up the planet-forming disc surrounding them, so that rings that are inclined and deformed to one another have formed. This suggests that there could be some planets in the universe that orbit groups of central stars in a bizarre way.
In a famous scene from the Star Wars film series, Luke Skywalker watches a double sunset on the fictional planet Tatooine. It has been clear for some time that there are planets with two suns and even more exotic constellations with more stars in the center seem possible. An interesting question is how planetary systems with several central stars could be structured and how they are formed. The current study now provides relevant insights. She directs her gaze to the GW Orionis system, which is located around 1,300 light years away from us in the constellation Orion.
This system of three orbiting stars and the material surrounding them has been the focus of an international team of astronomers for some time. In order to investigate the trio’s gravitational dance, instruments from the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile were used. “We found that the three stars are not circling in the same plane, but that their orbits are offset to each other and to the disk,” says co-author Alison Young from the University of Leicester. The researchers then also targeted the system with the Atacama Large Millimeter / Submillimeter Array (ALMA). So they were finally able to depict the planet-forming disk in detail.
Three suns mess up their nursery
It turned out that, in contrast to the orientation of our planetary system, the disk is anything but flat: “The images show an extreme case in which the disk is deformed and has a crooked ring that has detached from the disk,” says team leader Stefan Kraus from Exeter University. The oblique ring is located in the inner part of the disk near the three stars. “In our pictures we see the shadow of the inner ring on the outer disk. At the same time, the ALMA data allowed us to grasp the exact shape of the ring that is casting the shadow. From the combination of this information, we were then able to derive the three-dimensional orientation of the obliquely aligned ring and the warped shape of the disk, ”explains the researcher.
As the team further reports, the data analyzes also show that the inner ring contains around 30 masses of material. The scientists emphasize that it has enough substance to form planets. “All planets that form within the tilted ring will orbit the star in very inclined orbits,” explains co-author Alexander Kreplin from the University of Exeter.
To understand how the system could have come about, the astronomers also combined the observation data with computer simulations. As they report, the observed shifts fit the theoretically postulated “window tearing effect”. Specifically, the simulations show that the shift in the orbits of the three stars could lead to the disk around the three stars breaking into different rings.
Are there many exotic worlds in space?
Yet another factor may also shape the system. GW Orionis was already the focus of a study https://iopscience.iop.org/article/10.3847/2041-8213/ab8eb4, which was published in May of this year and is also based on ALMA observations of the ring system and simulations of the formation of the system included. “Our simulations show that the gravitational force of the star trio alone cannot explain the misalignment observed,” says Nienke van der Marel from the University of Victoria, who was involved in this study. “We think that the presence of a planet between these rings is necessary to explain why the disk was torn apart,” says the scientist.
Both teams are now hoping for further observational data that will provide new insights into the GW Orionis system and perhaps confirm the existence of young planets. They expect a lot from the keen eye of ESO’s Extremely Large Telescope (ELT), which is due to go into operation this decade. As more than half of the stars in the firmament are born with one or more companions, the prospects are exciting, say the scientists: There could be many exoplanets orbiting their stars on very inclined and distant orbits. “We forecast that many such exotic species will be discovered in future observation campaigns, for example with the ELT,” says Kreplin.
Video: ESO
Source: ESO, National Radio Astronomy Observatory, technical article: Science, doi: 10.1126 / science.aba4633