We report the discovery of an eclipsing binary system with mass-ratio q \sim 0.07 .
After identifying a periodic photometric signal received by WASP , we obtained CORALIE spectroscopic radial velocities and follow-up light curves with the Euler and TRAPPIST telescopes .
From a joint fit of these data we determine that EBLM J0555-57 consists of a sun-like primary star that is eclipsed by a low-mass companion , on a weakly eccentric 7.8-day orbit .
Using a mass estimate for the primary star derived from stellar models , we determine a companion mass of 85 \pm 4 M _ { Jup } ( 0.081 M _ { \odot } ) and a radius of 0.84 ^ { +0.14 } _ { -0.04 } R _ { Jup } ( 0.084 R _ { \odot } ) that is comparable to that of Saturn .
EBLM J0555-57Ab has a surface gravity \log g _ { \mathrm { 2 } } = 5.50 ^ { +0.03 } _ { -0.13 } and is one of the densest non-stellar-remnant objects currently known .
These measurements are consistent with models of low-mass stars .