Sh2-101 was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae. It is a H II region emission nebula located in the constellation Cygnus the Swan, and is also called the Tulip Nebula because it resemble the outline of a tulip. It is 70 light-years across and lies at a distance of about 6,000 to 8,000 light-years from the Earth, some 2 degrees southwest of the Crescent Nebula (NGC 6888), and inside the Orion spiral arm of our galaxy.
The star that excites the Tulip Nebula area is HDE 227018, and It is the bright star very near the blue arc at the cosmic tulip’s center. Red, green, and blue hues map emission from ionized sulfur, hydrogen, and oxygen atoms. Ultraviolet radiation from young, energetic stars at the edge of the Cygnus OB3 association, including O star HDE 227018, ionizes the atoms and powers the emission from the Tulip Nebula.
Sh2-101, at least in the field seen from earth, is in close proximity to microquasar Cygnus X-1, site of one of the first suspected black holes. It is the brighter of the two stars (lower star) in close vertical proximity just to the right of Sh2-101 in the image presented here. It is also a binary system, consisting of HDE 226868, a large blue super giant, and a companion that is thought to be a “black hole”. The more compact of the two objects in the system is thought to be between 20 and 35 solar masses. Since the largest possible mass of a neutron star cannot exceed three solar masses, the compact object is almost certainly a black hole. HDE 226868, is an O9-B0 supergiant with a surface temperature of 31,000 kelvins, comprising about 20-40 solar masses. These two objects share an orbital periodicity of 5.6 days. The matter being stripped off HDE 226868 by the black hole’s powerful gravity forms an accretion disk around the black hole, as well as forming an associated wind corona from the blue supergiant. This process results in the plentiful X-ray emissions that were first discovered 30 years ago.
Credits: NASA, Wikipedia.