The Tulip Nebula

That time when Stephen Hawking lost a bet: tales of a nebula, a powerful X-ray source, a bowshock and a black hole.

This photograph of SH 2-101 (a.k.a. the Tulip Nebula) might be nice to look at, but the story behind it is equally captivating! The Tulip nebula has all the hallmarks of nebulae, including the distribution of gases, dust, star creation and intense processes all over. It's a 6000 year old still of a very dynamic process with a surprise hiding in it.

Discovery of the nebula and Cygnus X-1

Astronomer Stewart Sharpless first added this nebula as late as 1959, which is relatively late considering the Herschels already catalogued most of the nebulae from the 1780's onward. At that moment it was "just another faint nebula".

That changed in the early 1960's! Two Aerobee rockets carrying Geiger counters discovered Cygnus X-1, a mysterious X-ray source in the constellation Cygnus. NASA's Uhuru satellite later revealed its rapid X-ray flickering, suggesting something compact and powerful—a likely black hole. Further studies in 1971 confirmed Cygnus X-1’s location near a supergiant star. By 1973, it was recognized as the first strong black hole candidate, showing signs of an accretion disk.

A high stakes bet!

Around 1975 Cygnus X-1 was the subject of a high stakes bet between physicists Stephen Hawking and Kip Thorne. Hawking bet against the existence of black holes in the region. He conceded the bet in the late 80's, costing him a year's subscription of a magazine about heavenly bodies called "Penthouse". Cygnus X-1 was the first confirmed black hole ever, and has since become a key to understanding black holes and their role in both stellar systems and distant galaxies.

There goes the neighborhood...

We now know that the supergiant variable star designated as V1357 Cyg is 21 solarmasses and 20 times as large as our sun (so a radius of 14 million kilometers). It forms an abusive relationship with the microquasar Cygnus X-1, which is 15 solar masses and has a radius of just 45 kilometers! At a distance of 0.2 AU (so really close!!) they orbit their center of mass at the stunning speed of 5.6 days. And to avoid confusion: Microquasars contain a black hole. Let's just say it's the celestial equivalent of a TurDucken.

Cygnus X-1, being a black hole, pulls matter from companion star V1357 Cyg and forms an accretion disk. This becomes so hot due to friction, that it begins to emit X-rays. The disk also projects narrow streams or "jets" of subatomic particles at near-light speed, generating a strong radio wave emission.

A bowshock!

The distinctive blue arc on the lower rights side of the Tulip Nebula (which actually is more of a sphere) is called a bowshock, and it's the result of the so called relativistic stream of energetic particles.

While the jet itself is narrow and focused, the bowshock it creates is spherical because of how the jet's energy is deposited into and propagates through the surrounding medium (interstellar space). The shockwave spreads outwards in all directions, forming a sphere-like structure.

SH 2-101; a pretty face with stories to tell!


About the Tulip Nebula

  • Right ascension: 20h 00m 29.37s

  • Declination: 35° 19′ 13.9″

  • Distance: 6,000 ly

  • Size:

  • Apparent magnitude (V): 9.0

  • Apparent dimensions (V): 16' x 9'

  • Constellation: Cygnus

  • Designations: Sharpless 101, Sh 2-101, Cygnus Star Cloud


About the photo

122 images of 5 minutes each

  • Aquired over x nights between x and y
  • Total integration time x hours
  • Imaging location: Zaltbommel (NL)
  • Taken under a Bortle 6.4 sky

Equipment used

  • Imaging telescope:
    TS Optics Apochromatic 115/800 mm PHOTOLINE with a 0.79x Focal reducer resulting in F/5.5@623mm Focal lenght
  • Imaging camera:
    ZWO ASI183MC Pro (CMOS)
  • Mount:
    Equatorial iOptron GEM45
  • Guiding telescope:
    William Optics Refractor 200 Guidescope AC 50/200
  • Guiding camera:
    ZWO Optical ASI290mm Mini (CMOS)
  • Filters:
    Optolong L-Ultimate 2.00" 3nm
  • Processed in PixInsight