The widest ultracool binary

Aims. I test the ejection scenario for the formation of brown dwarfs and low-mass stars through the detection of a very wide ultracool binary. Methods. LEHPM 494 (M6.0 +/- 1.0 V) and DENIS-PJ0021.0-4244 (M9.5 +/- 0.5 V) are separated by 1.3 arcmin and are high proper motion co-moving ultracool stars. I have used six astrometric epochs spaced by 22 years to confirm their common tangential velocity. Results. The angular separation between both low-mass stars remains constant with an uncertainty of less than 0.1%. I have also derived their most probable heliocentric distance (23 +/- 2 pc), age interval (2 - 10 Ga) and masses (0.103 +/- 0.006 and 0.079 +/- 0.004 M (circle dot)). The pair, with a projected physical separation of 1800 +/- 170 AU, is by far the widest ultracool binary yet found in the field. Conclusions. This serendipitous and simple detection is inconsistent with ultra low-mass formation ejection scenarios and complements current searches for low-mass tight binaries.