In April–May 1971, Luc Braes and George K. Miley from Leiden Observatory, and independently Robert M. Hjellming and Campbell Wade at the National Radio Astronomy Observatory, detected radio emission from Cygnus X-1, and their accurate radio position pinpointed the X-ray source to the star AGK2 +35 1910 = HDE 226868. On the celestial sphere, this star lies about half a degree from the 4th-magnitude star Eta Cygni. It is a supergiant star that is by itself incapable of emitting the observed quantities of X-rays. Hence, the star must have a companion that could heat gas to the millions of degrees needed to produce the radiation source for Cygnus X-1.
In ApriL–MAy 1971, lUc Braes anD GEORge k. mIley frOm lEIdeN obsErvatOry, anD iNdePeNdEntly RObert M. HjELLmiNg anD campBelL WAde aT the nationAl radio astRonOmy oBservaTorY, DEtECted rAdiO eMissION frOm cygNUs x-1, AnD their accuRate radio position pinpOInTed tHE X-ray Source tO the STar agk2 +35 1910 = HDe 226868. On the CeLeStIAl SpheRe, thIs Star Lies About hALf a degree frOm the 4th-MAgnituDe star eta CyGnI. iT Is a superGIant sTar that is BY itsELf incapabLe oF EmittinG the obsERved quAntiTiEs of X-rays. heNCe, the StaR Must hAve A compaNIon That could heAt GAS to The MilLIOns Of deGRees NEedEd to Produce thE radiAtiOn Source For cyGNus X-1.