Michael A. Stecker


Cygnus X-1 and Sharpless-101
The red emission nebula Sh2-101 (RA 19 hrs 59.9 min and Dec. +35 degrees 17.5 min) is
found within the borders of  Barnard 144 in the rich Cygnus Star Cloud.  Southeast of this
nebula is a strong x-ray source called Cygnus X-1.  This source is a binary system (distant
of 2.5 kpc) consisting of the O9.7 Iab type supergiant HDE 226868 (star arrowed in the
photo above).  Orbiting this star is a compact optically invisible object with a period of 5.6
days. The mass of the unseen companion, significantly larger then 5 solar masses, suggests
that it may be a black hole.  An excellent source of information about Cygnus X-1 can
be found at:
Photographic Data: An Astrophysics 155 mm f/7 EDF refractor and Nikon F2 camera were used with unhypersensitized Kodak Pro 400 PPF film (35 mm format).  Two 50-minute exposures were made. The negatives were stacked, processed, and cropped in the computer.