  As the brightest O-type X-ray source in the Carina nebula, HD 93250 (O4
III(fc)) is X-ray overluminous for its spectral type and has an unusually hard
X-ray spectrum. Two different scenarios have been invoked to explain its X-ray
properties: wind-wind interaction and magnetic wind confinement. Yet, HD 93250
shows absolutely constant radial velocities over time scales of years
suggesting either a single star, a binary system seen pole-one or a very long
period and/or highly eccentric system. Using the ESO Very Large Telescope
Interferometer, we resolved HD 93250 as a close pair with similar components.
We measured a near-infrared flux ratio of 0.8+/-0.1 and a separation of
1.5+/-0.2 x 10E-03 arcsec. At the distance of Carina, this corresponds to a
projected physical distance of 3.5 A.U. While a quantitative investigation
would require a full characterization of the orbit, the binary nature of HD
93250 allows us to qualitatively explain both its X-ray flux and hardness and
its non-thermal radio emission in the framework of a colliding wind scenario.
We also discuss various observational biases. We show that, due to
line-blending of two similar spectral components, HD 93250 could have a period
as short as one to several years despite the lack of measurable radial velocity
variations.
