Exoplanet is first found in a quadruple system

A massive planet, 15 times larger than Jupiter, has been directly imaged revealing a complex cosmic dance involving 4 celestial bodies.

The exoplanet was found in a star system called HIP 81208. It is described in a paper published in the journal Astronomy & Astrophysics.

HIP 81208 has been known to astronomers for a long time and is 477 light-years from Earth.

Image of distant star exoplanet with labels
HIP 81208, as captured by ESO’s Very Large Telescope. Credit: ESO/A. Chomez et al.

At its centre is the blue-white star HIP 81208 A, nearly 3 times bigger than the Sun. Orbiting this star is a red dwarf, about 8 times smaller than the Sun, and a brown dwarf less than 15 times the size of the Sun.

But it was not until the European Southern Observatory’s (ESO) Very Large Telescope in Chile snapped a picture of the system that astronomers noticed a fourth object in the system – a planetary mass body orbiting the red dwarf.

The gas giant has a radius only slightly larger than our solar system’s largest planet, Jupiter, but weighs 14.8 times as much.

HIP 81208 represents a unique stellar system described in an ESO blog post as an “hierarchical quadruple system” – one with two stars and two smaller bodies orbiting each one.

The mass of the newly discovered exoplanet sees it sit right at the border between a planet and a brown dwarf – “failed stars” – too small to fuse hydrogen into helium in their cores.

It was found when a team of astronomers re-analysed data from the VLT’s Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. Instead of looking for exoplanets using indirect methods, such as measuring the “wobble” of host stars caused by the weaker gravity of an orbiting exoplanet, SPHERE directly images systems.

HIP 81208 is the first hierarchical quadruple system to be directly imaged.

Astronomers believe studying the celestial quartet will help them understand how complex systems like it form and evolve, while also informing physicists about the theoretically complicated dynamics of many-body arrangements.

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