Roche lobe

plural Roche lobes

1. astronomyThe teardrop-shaped region around a star in a binary system within which orbiting material is gravitationally bound to that star.

   If only one component accurately fills its Roche lobe the system is semi-detached. If neither fills its Roche lobe, it is detached.

   2013, Josef Kallrath, Eugene F. Milone, Eclipsing Binary Stars: Modeling and Analysis, page 85

   2 more examples

   A further interesting situation (although not one of much relevance for this book) comes about if both stars for some reason fill their Roche lobes simultaneously.

   2002, Juhan Frank, Andrew King, Derek Raine, Accretion Power in Astrophysics, page 54

   Generally, mass transfer by Roche lobe overflow is required to power LMXRB's, since low mass stars never exhibit strong stellar winds.

   2012, C. de Loore, C. Doom, Structure and Evolution of Single and Binary Stars, page 386

2. broadlyastronomyAround any two astronomic entities in a "binary system", a teardrop-shaped region, within which orbiting material is gravitationally bound to that entity.

   In the accretion disk model, a circumjovian disk forms as solar nebula gas and entrained solid particles (dust to boulder-size) flow through the growing planet's Roche lobes to feed Jupiter during the rapid (runaway) gas-capture phase of core accretion [...].

   2023, Rosaly M. C. Lopes, Katherine de Kleer, James Tuttle Keane, Io: A New View of Jupiter’s Moon, page 43