Identification of 2U0525 – 06 with 2Orionis

Abstract

BLACK holes may be observed in the X-ray band1 and the discovery of X-ray sources in binary systems with non-luminous massive companions is the most convincing evidence of existence of black holes2–5. We have compared the Trimble and Thorne lists6 of collapsed star candidates with the Uhuru catalogue of X-ray sources7. Trimble and Thorne considered only systems with unseen secondary stars of mass M2 > 1.4 M⊙ in the catalogue examined8. We have found that four of these objects fall within 3 arc deg of X-ray sources (Table 1). υ2 Orionis (Fig. 1) is the only one of the four which is inside the error box of an X-ray source (2U0525–06).