The Tulip Nebula (Sh2-101 or the Cygnus Star Cloud) is a bright emission nebula located about 6,000 light-years away in the constellation Cygnus, 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.
It is called the Tulip Nebula because it appears to resemble the outline of a tulip when imaged photographically. It was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae.
The Tulip nebula, at least in the field seen from earth, is in close proximity to Cygnus X-1, a binary system and the brightest source of hard X-rays in our sky. It is site of one of the first suspected black holes. (Cygnus X-1 can be seen as the righter one of two bright stars on the right side of the Tulip – not the even brighter stars on the top of this image.)
Over the years the location of this X-ray source became more accurately determined. The X-ray source was found to lie very close to the position of a 9th magnitude star called HD 226868. This star is a large blue super giant, and its companion – 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 can not exceed three solar masses, the compact object which is unseen, is almost certainly a black hole. These two objects share an orbital periodicity of 5.6 days.
Image Credit & Copyright: J-P Metsavainio (http://astroanarchy.zenfolio.com/)