Sh 2-101

Lore & Background

Sh 2-101 was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae. It is an H II region, a cloud of ionized gas that emits light. The nebula is sometimes called the Tulip Nebula because its photographic appearance resembles the outline of a tulip.

It lies at a distance of about 6000 light-years from Earth. In the field as seen from Earth, Sh 2-101 is in close proximity to the microquasar Cygnus X-1, which is located about west of the nebula. Cygnus X-1 is the site of one of the first suspected black holes. The companion star of Cygnus X-1 is a spectral class O9.7 Iab supergiant with a mass of 21 solar masses and 20 times the radius of the Sun.

The binary system has a period of 5.8 days, and the pair is separated by 0.2 astronomical units. The black hole has a mass of 15 solar masses and a Schwarzschild radius of 45 km. A bowshock is created by a jet of energetic particles from the black hole as they interact with the interstellar medium; this bowshock can be seen as an arc at the top of the photo.

Reader's Guide

Sh 2-101's significance lies in its association with Cygnus X-1, one of the first suspected black holes, which provides a rare opportunity to study the interaction between a black hole's jet and the surrounding interstellar medium. The bowshock visible in the nebula is a direct result of energetic particles from the black hole colliding with the gas of Sh 2-101, offering a tangible example of how black holes influence their environment. The nebula itself, catalogued by Stewart Sharpless in 1959, is a classic H II region, and its distinctive tulip shape makes it a recognizable target for astrophotographers.

The proximity of the two objects—the emission nebula and the microquasar—allows astronomers to observe the effects of a black hole on a nearby nebula, including the formation of a bowshock. The companion star of Cygnus X-1, a massive O9.7 Iab supergiant, and the black hole's mass of 15 solar masses provide key data for understanding binary systems and black hole formation. The nebula's legacy is tied to its role in illustrating the dynamic processes of star formation and black hole activity within the same field of view.