Astronomers observing binary star system inadvertently discover exoplanet

In distant orbit around double star system, newly-detected object may be a giant planet or a brown dwarf.
By Laurel Kornfeld | May 10, 2018
Astronomers studying the young binary star system CS Cha inadvertently discovered a small, infant exoplanet in the dust disk surrounding the two stars.

Using the European Southern Observatory's (ESO) adaptive optics Spectro-Polarimetric-High-Contrast Exoplanet REsearch (SPHERE) instrument on the Very Large Telescope (VLT) in southern Chile, an international team of scientists led by Dutch researchers at Leiden University searched the disk surrounding the binary looking for evidence of new planets forming.

Located about 600 light years away in the southern hemisphere constellation Chameleon, the binary star system is only two to three million years old.

"The most exciting part is that the light of the (planet) companion is highly polarized. Such a preference in the direction of polarization usually occurs when light is scattered along the way. We suspect that the companion is surrounded by his own dust disc. The tricky part is that the disc blocks a large part of the light, and that is why we can hardly determine the mass of the companion. So it could be a brown dwarf but also a super-Jupiter in his toddler years. The classical planet-forming models can't help us," explained Christian Ginski of Leiden University and lead author of a study on the finding accepted for publication in the journal Astronomy and Astrophysics.

Brown dwarfs are considered the lowest end of the stellar classification system. If the suspected planet is actually a brown dwarf, then the CS Cha is a triple star system.

Developed in the Netherlands, SPHERE is capable of directly imaging exoplanets in dust disks surrounding stars by observing polarized light reflected by either the planets' atmospheres or the dust disks.

In a distant orbit around the binary, the planet is located more than 214 times as far from the two stars as Earth is from the Sun.

After finding the planet in their images, the researchers looked at photos of the same system taken 19 years ago with the Hubble Space Telescope (HST) and 11 years ago with the VLT. They found the planet in both sets of images and successfully determined it moves with the double star system.

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