Sharpless 101 (specifically Sh2-101) is also known as the Tulip Nebula and is located approximately 6000 light-years away in the constellation of Cygnus (The Swan). Stewart Sharpless first cataloged this rich H II emission region in 1959 in his second catalog of nebulae. Early photographic images of this area resembled a flower, and this gave rise to its common name.
Also in this region is the first black hole ever discovered, Cygnus X-1. First detected in 1964 from an x-ray instrument sent aloft on a sounding rocket, Cygnus X-1 was the brightest x-ray source seen from Earth. In 1971 radio signals were detected and these were used to locate the x-ray source as coming from a star known as HDE 226868. This star is a supergiant but alone, does not have the ability to produce the energetic x-rays seen. It was concluded that HDE 226868 must have a dark companion with the ability to heat gases in the system to the millions of degrees of temperature necessary to produce x-rays. Measures of doppler shift in the spectrum of HDE 226868 allowed the orbits of the star and its companion to be determined and based on the mass required for these observed orbits - and the fact there was no light signature from its companion - it was proposed that Cygnus X-1 was indeed a back hole - potentially the first-ever detected! It is now believed that Cygnus X-1 is pulling gas from its companion towards its event horizon. This spinning superheated disk of gas is the engine that produces the x-rays seen from Earth.
Interesting bit of trivia: in 1974, Kip Throne famously bet Stephen Hawking that Cygnus X-1 was a black hole. In 1990 Hawkings conceded that X-1 was a black hole and Throne won the bet.
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