![Figure 1: Trailed intensity image showing the orbital evolution of two emission lines in MWC 656. Fe II 4,583 Å is formed in the equatorial disc of the Be star while He II 4,686 Å arises from gas encircling the companion black hole. Figure 1: Trailed intensity image showing the orbital evolution of two emission lines in MWC 656. Fe II 4,583 Å is formed in the equatorial disc of the Be star while He II 4,686 Å arises from gas encircling the companion black hole.](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/news/resultados127_137.jpg?itok=ScaT7W8C)
Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the ~80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as
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