1. Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 306-438, 4800 Oak Grove Drive, Pasadena, California 91109, USA
2. 525 Davey Laboratory, Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, Pennsylvania 16802-6305, USA
3. Astrophysics and Planetary Science, University of Colorado, Boulder, Colorado 80309, USA

Correspondence to: Steven H. Pravdo¹ Correspondence and requests for materials should be addressed to S.P. (e-mail: Email: spravdo@jpl.nasa.gov).

Herbig–Haro (HH) objects have been known^{1, 2} for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars³, stellar winds clashing with nebular material⁴, dense pockets of interstellar gas excited by shocks from outflows⁵, and interstellar 'bullets' (ref. 6). Recent progress has been made with the jet-induced shock model⁷, in which material streams out of young stellar objects and collides with the surrounding interstellar medium. A clear prediction of this model is that the most energetic Herbig–Haro objects will emit X-rays, although they have not hitherto been detected⁸. Here we report the discovery of X-ray emission from one of the brightest and closest Herbig–Haro objects, HH2, at a level consistent with the model predictions. We conclude that this Herbig–Haro object contains shock-heated material located at or near its leading edge with a temperature of about 10⁶ K.