The Night Sky - Episode 20
THE TULIP NEBULA
This is episode 20 in my series on our night sky
The universe never ceases to amaze with its wonders and artistry, and the Tulip Nebula (Sh2-101) is no exception. Let me take you on a journey through this curious region of space, home to one of the most enigmatic of cosmic phenomena - black holes.
The Tulip Nebula
A total of 116 exposures of 3 minutes each, for a total of about 6 hours of data, were shot to complete this image.
Image by Achint Thomas
The Tulip Nebula is an emission nebula located approximately 6,000 light-years away from Earth in the constellation Cygnus. Spanning roughly 70 light-years across, it appears about 16 arcminutes wide in the night sky—a size comparable to just over half the apparent diameter of the full Moon. Its brightness makes it a challenging but rewarding target for astrophotographers, with its ethereal glow stemming from ionized hydrogen gas. In the northern hemisphere, the nebula is best observed during the summer months, particularly from late June through early September, when the constellation of Cygnus graces the zenith of our night skies.
Locating the Tulip Nebula
Cygnus (the Swan constellation) has been a subject of fascination for millennia. Stories can be found in various mythologies, including Greek, Roman, and Middle-Eastern. To locate Cygnus in the sky, we need to look for the prominent cross-like shape known as the Northern Cross, with its brightest star, Deneb, marking the tail of the swan. During summer evenings in the northern hemisphere, Cygnus can be found soaring high overhead, nestled along the dense star fields of the Milky Way. The constellation’s distinctive shape and rich stellar population make it a favorite for stargazers and astrophotographers alike.
Location of the Cygnus constellation in the night sky. The image is at a 14mm field-of-view.
Image by Achint Thomas
The Tulip Nebula resides in a particularly hydrogen-rich region of the Milky Way. The Veil Nebula, a stunning supernova remnant with intricate filamentary structures, showcases the aftermath of a massive stellar explosion. The North America Nebula, with its striking resemblance to the continent, glows brightly with hydrogen emission. The Pelican Nebula, situated nearby, is a dynamic region of star formation shaped by ultraviolet radiation. The Crescent Nebula, created by the winds of a Wolf-Rayet star, displays a delicate shell-like structure. WR-134, a lesser-known Wolf-Rayet star, is surrounded by faint nebular emissions. Finally, the Butterfly Nebula, named for its wing-like appearance, captivates with its symmetrical beauty and vibrant colors.
Location of the Tulip Nebula in the constellation of Cygnus.
Image by Achint Thomas
We can see the Tulip Nebula as another beautiful structure in this busy region of space.
Cygnus X-1: A Stellar Black hole
Located near the Tulip Nebula, Cygnus X-1 is one of the first black holes discovered and remains one of the most studied. Discovered in 1964 as a strong X-ray source, its enigmatic nature led astronomers to uncover its origin. Observations revealed that it is part of a binary system with a massive blue supergiant, HD 226868. The supergiant's orbit hinted at an invisible yet compact and immensely massive companion. With a calculated mass of around 21 times that of the Sun, this object was far too heavy to be a neutron star or white dwarf, leading to the only other possibility, a black hole—a revelation that profoundly influenced our understanding of these cosmic phenomena.
Location of one of the earliest discovered black holes, Cygnus X-1, near the Tulip Nebula. The magnified region shows the bowshock created by the black hole.
Image by Achint Thomas
Interestingly, Cygnus X-1 became the subject of a playful bet in the 1970s between renowned physicists Stephen Hawking and Kip Thorne. Hawking bet against Cygnus X-1 being a black hole, while Thorne argued in favour of it. Over the decades, mounting evidence, including the motion of its companion star and its intense X-ray emissions, pointed conclusively to its black hole nature. By 1990, Hawking conceded the bet. Subsequent advances in technology further strengthened the case, and in 2021, precise measurements of its mass, distance, and spin finally confirmed Cygnus X-1 as a stellar-mass black hole.
The X-ray emissions from Cygnus X-1 arise from the black hole’s accretion disk, where material siphoned off the companion star spirals inward, heating up to millions of degrees. This discovery provided a clear picture of how stellar-mass black holes interact with their surroundings. Further studies showed Cygnus X-1’s incredible spin, approaching the theoretical limit, and even revealed relativistic jets—beams of energy streaming from near the black hole’s poles. These jets collide with the surrounding gas, creating a “bowshock” which can be photographed and observed.
Today, Cygnus X-1 stands as a testament to human ingenuity, offering profound insights into the life cycles of massive stars and the nature of spacetime itself.
The Capture Process
To capture the Tulip Nebula, I used a dedicated cooled astro camera, the ZWO ASI533MC Pro, paired with a 400mm lens. My setup included a star tracker equipped with auto-guiding to ensure pinpoint accuracy during long exposures. A dual-narrowband filter was essential to isolate the hydrogen-alpha (Hα) and oxygen-III (OIII) emission lines, enhancing the nebula’s intricate details while minimizing light pollution. Filters with tighter bandpasses—such as 3nm or 5nm—offer even greater contrast by allowing only the specific wavelengths of interest to pass through, effectively blocking unwanted light from nearby sources or moonlight. For this project, I used the Optolong L-Ultimate filter.
Light transmission curve of the Optolong L-Ultimate filter, a typical dual-narrowband filter. It is designed to allow the transmission of Hα (656.3 nm), Hβ (486.1 nm) and OIII (500.7 nm and 495.9 nm) wavelengths while suppressing all other wavelengths. The tight bandpass of 3nm ensures maximal rejection of light pollution and moonlight.
Over two clear nights, I collected about 6 hours of exposure data, meticulously stacking and processing the images to reveal the nebula’s radiant structure.
Astrophotography is a gateway to the universe, and the Tulip Nebula is a testament to the beauty and mystery of the cosmos. Whether you’re an experienced observer or a beginner with a telescope, I encourage you to seek out this cosmic flower. Let the vibrant colours and intricate patterns of the nebula remind you of the boundless wonders waiting to be discovered in our night skies. Clear skies and happy stargazing!
Check out some other nebulae I have captured.
Capture details
Camera: ZWO ASI 533MC Pro
Gain: 100
Sensor Temperature: -10°C
Lens: Sigma 100-400mm f/5-6.3 DG OS HSM
Focal length: 400mm (equivalent to 640mm full-frame)
f-Ratio: 6.3
Sub-exposure length: 180 seconds
Number of exposures: 116 (Optolong L-Ultimate filter)
Total integration time: ~6 hours
Calibration frames: 30 darks, 30 flats, 30 dark flats
Mount: SkyWatcher Star Adventurer GTi
Guide camera: ZWO 120mm mini
Guide scope: ZWO Mini Guide scope
Capture control: ZWO ASIAir Pro
Dew control: SvBony dew heater
Field Power: AIMTOM 194Wh Portable Power Station
Sky quality: Bortle 5
Moon phase: Various (95%, 25%)
Processing: PixInsight