We are closer to understanding how “Tatooine Planets” form

Hyperaxion Mar 23, 2020

Scientists have observed different types of orbits around binary stars, which may give rise to planets similar to Luke Skywalker’s homeland.

If you’re a fan of the Star Wars saga, you know that Tatooine – Anakin Skywalker’s home planet – orbits two suns. Well, since 2011, we know that, in real life, there many planets like that in space. What remains a mystery to scientists is the conditions under which they are formed. After all, it is more common to study the formation of planets that orbit a single star.

Two orbits captured by the ALMA telescope. On the left, the disk is misaligned with internal binary stars. The stars have been orbiting each other for 315 days. On the right, the disk is aligned with the orbit of its binary stars. The stars are orbiting each other in 13.6 days.
Two orbits captured by the ALMA telescope. On the left, the disk is misaligned with internal binary stars. The stars have been orbiting each other for 315 days. On the right, the disk is aligned with the orbit of its binary stars. The stars are orbiting each other in 13.6 days.

Thanks to observations with the ALMA telescope in Chile, scientists were able to analyze how the discs of matter, made up of gas and dust, behave around these binary stars and, in the future, may give rise to the planets that revolve around them. These are called circumbinary discs.

With that, researchers at the University of California, Berkeley, and other American institutions have taken another step to learn how planets form in different environments.

Understanding the orbit

Astronomers already know that the orbits of binary stars can deform and tilt the disk around them, resulting in a misalignment in relation to the orbital plane of their host stars.

In an article published in the scientific journal The Astrophysical Journal, astronomers at the University of California used ALMA data to determine the degree of alignment of nineteen protoplanetary disks around binary stars. “With our study, we wanted to learn more about the typical geometries of circumbinary disks,” said researcher Ian Czekala.

The team compared ALMA data to the twelve “Tatooine planets” previously found by the Kepler Space Telescope. As a result, the group found that the degree to which the binary stars and their circumbinary disks are misaligned depends largely on the orbital period of the host stars.

Thus, the shorter the orbital period of the binary star, the greater the probability of hosting a disk aligned with its orbit. Meanwhile, those with periods longer than a month usually host misaligned discs, as you can see in the image above.

Next steps

The next step in the study, according to the scientists, is to try to find out why there is such a strong correlation between the alignment of the disk and the orbital period of the binary star. “We want to use existing and future installations, like ALMA and the next generation of the Very Large Array [a radio astronomy observatory located on the Plains of San Agustin, USA], to study disk structures with higher levels of accuracy,” says Czekala. With that, it would be possible to try to understand how the deformed or tilted disks affect the formation of planets in these conditions.

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