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 \pm 0.1 and a separation of 1.5 \pm 0.2 \times 10 ^ { -3 } 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 .