A team of scientists led by University of Florida astronomer Dr. Bo Ma has discovered the first ‘binary-binary’ system — two massive companions around one star in a close binary system.
Artist’s conception of a binary system with a brown dwarf and a giant planet. Image credit: NASA / JPL-Caltech.
HD 87646 is a binary stellar system approximately 240 light-years away from the Sun.
The primary star in the system, HD 87646A, is bright G-type star with about 1.12 times the mass of the Sun. It is only 22 AU (astronomical units) away from the secondary star, HD 87646B, a fainter K-type star with about 0.9 times the mass of the Sun.
“HD 87646 is the first known system to have two massive substellar objects (a giant planet and a brown dwarf) orbiting a star in a close binary system,” Dr. Ma and co-author said.
The newly-discovered giant planet, called MARVELS-7b, is 12 times the mass of Jupiter, while the brown dwarf, MARVELS-7c, has 57 times the mass of Jupiter.
The two giant companions take 13.5 and 674 days to orbit their parent star, HD 87646A, and are about 0.1 and 1.5 AU from it.
“For such large companion objects to be stable so close together defies our current popular theories on how solar systems form,” the researchers said.
Astronomers think that planets in our Solar System formed from a collapsed disk-like gaseous cloud, with our largest planet, Jupiter, buffered from smaller planets by the asteroid belt.
In HD 87646, the two giant companions are close to the minimum mass for burning deuterium and hydrogen, meaning that they have accumulated far more dust and gas than what a typical collapsed disk-like gaseous cloud can provide. They were likely formed through another mechanism.
The survey of HD 87646 occurred in 2006 during the pilot survey of the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) of the SDSS-III program.
It has taken eight years of follow-up data collection through collaboration with over 30 astronomers at seven other telescopes around the world and careful data analysis to confirm what they call a ‘very bizarre’ finding.
The discovery was announced Oct. 7, 2016 in the Astronomical Journal (arXiv.org preprint).
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Bo Ma et al. 2016. Very Low-Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS VI: A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646. AJ 152, 112; doi: 10.3847/0004-6256/152/5/112
