This word is acceptable for play in the UK dictionary that is being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The point at the centre of a system; an average point, weighted according to mass or other attribute. The term is usually used in astronomy for the centre of mass about which a system rotates, for example, the moon and the earth rotate about a common point within the earth but not near the centre. Jupiter and the Sun rotate about a common point just outside the surface of the Sun.

"Gemenon is the twin planet of Caprica, the two circling a gravitational barycentre as they circle their central star."

centre of mass    centre of gravity    orthocentre    centroid   

barycenter