A binary merger origin for inflated hot Jupiter planets

E. L. Martin¹, H. C. Spruit² and R. Tata³

¹ Centro de Astrobiologia CSIC – INTA, Carretera Torrejón-Ajalvir km 4, 28850 Madrid, Spain
² Max-Planck-Institut für Astrophysik, 85748 Garching, Germany
e-mail: henk@mpa-garching.mpg.de
³ Instituto de Astrofisica de Canarias, calle Via Lactea, 38200 La Laguna, Tenerife, Spain

Received: 16 March 2011
Accepted: 27 August 2011

Abstract

We hypothesize that hot Jupiters with inflated sizes represent a separate planet formation channel, the merging of two low-mass stars. We show that the abundance and properties of W UMa stars and low mass detached binaries are consistent with their being possible progenitors. The degree of inflation of the transiting hot Jupiters correlates with their expected spiral-in life time by tidal dissipation, and this could indicate youth if the stellar dissipation parameter Q_∗^' is sufficiently low. Several Jupiter-mass planets can form in the massive compact disk formed in a merger event. Gravitational scattering between them can explain the high incidence of excentric, inclined, and retrograde orbits. If the population of inflated planets is indeed formed by a merger process, their frequency should be much higher around blue stragglers than around T Tauri stars.