Amateur Astronomers Discover the Titan Nebula: what could be the Third Largest Planetary Nebula in the Sky!

Located in the Andromeda constellation, the Titan Nebula is a gigantic shell of ionized gas extending over a portion of the sky as wide as 3 times the angular size of a full moon! Discovered by a team of three amateur astronomers from the USA, France and Germany, the Patchick-Strottner-Drechsler 9 nebula has been officially reported as a Planetary Nebula candidate in October 2021. If confirmed by upcoming spectroscopic measurements, the Titan Nebula could be the third largest Planetary Nebula ever detected in the sky!

Patchick-Strottner-Drechsler 9 or the Titan Nebula is a Planetary Nebula candidate, discovered by Dana Patchick (USA), Xavier Strottner (France) and Marcel Drechsler (Germany). Processing: Marcel Drechsler. Photo Credit: Andreas Zirke

Hunting for new celestial objects

In an era where the sky is being permanently monitored by tens of at least 4-meter class telescopes every night, it seems that the exciting discoveries of celestial objects made by keen stargazers from their backyards has come to an end. Considering the levels of light-gathering power and resolution these professional telescopes have or will have - such as next coming Vera C. Rubin telescope - it became clear enough that the equipment of amateur astronomers is being substantially outperformed. 

Even though amateur astronomers will never catch up with the high-tech instruments used by professional observatories, they still have something that real astronomers do not have: free time. Indeed, with the huge quantity of data that survey telescopes leave behind, there are still areas which remain unexplored just because they would have required more observing time to reveal what they could be hiding.

This is how the Titan Nebula was discovered. By attentively looking at digitized sky maps carried out by professional telescopes and released publicly on the internet, a team of amateur astronomers identified a potential white dwarf star. Since a white dwarf is the remnant core of a main sequence star ending its life, a shell of ionized gas is likely to be detected as well; in other words a planetary nebula could be found in its vicinity. Thus, began the search for a never observed nebula...

The discovery of the Titan Nebula (also Patchick-Strottner-Drechsler 9)

The Patchick-Strottner-Drechsler team initially analyzed ultraviolet images captured with the Galaxy Evolution Explorer telescope - also called GALEX -, a telescope aiming at studying star evolution in distant galaxies up to 80% way back to the Big Bang. They brought attention to one star of the field they were looking at since it had a strong UV emission. Retrieving more data about this star - with online database such as Aladin from Strasbourg Observatory - allowed them to start thinking it might have the appropriate age, temperature and distance to be classified as a white dwarf and hide a planetary nebula. 

UV light emitted from a white dwarf star triggers a ionization process onto the gas that was once expelled from the star's atmospheric layers. Ionization releases free electrons that mix up with the gas ions. After a specific amount of time, those electrons then recombine with the ions, emitting lower energy photons, thus producing a visible light glow at specific spectral lines. This emission of visible light is what makes a so called Planetary Nebula (or PN).  

In science, cross-checking multiple sources of data is always helpful to shed light on whether a hypothesis is valid or nor. The team therefore accessed data in the blue layer of the Digital Sky Survey (DSS) and ended up detecting a faint nebulous structure surrounding the 90,000-Kelvin white dwarf.  

    Image of the Titan Nebula assembled with a wider image of the starry sky showing the actual  position and angular size of the newly-discovered nebula. Credit: Andreas Zirke

They confirmed the discovery of the nebula - which is not yet labelled as a Planetary Nebula - at the beginning of 2021 when they obtained the first images. To do so, they relied on German astrophotographer Andreas Zirke who was in charge of acquiring the data in H-Alpha, Oxygen III, RVB and luminance layers. At least 15 hours of exposure time were required to make this faint nebula pop up of the sky background. Subsequent observations estimated its magnitude between 20 and 22 which is at least 2.5 Million times dimmer than the Great Orion Nebula!

The final image results in 128.73 hours total integration time and reveals a widespread bubble-like structure of gas that covers almost the entire field of view of the 430 mm focal length refractor telescope. Such extension surprised the team since it indicated the nebula is at least 1.5 degrees wide - or 90 arcmin. Such angular size is tantamount to 3 times the diameter of a full moon! 

Officially designated as Patchick-Strottner-Drechsler 9 or PaStDr 9 or PN-G : 140.4-21.2, the team also agreed on an evocative popular name: the Titan Nebula.

Is PaStDr 9 the third largest Planetary Nebula?

After its discovery, the Patchick-Strottner-Drechsler team immediately submitted the Titan Nebula as a Planetary Nebula (PN) candidate to Pascal Le Du, a French amateur astronomer who manages the PN inquiries from all around the world. PaStDr 9 is very likely a planetary nebula but is not considered as such as long as no spectroscopic data has confirmed it.

Planetary nebulae feature a peculiar pattern in their spectrum (Oxygen III, Nitrogen II...) whose intensity are directly linked to the properties of the star responsible of their formation.

The true nature of the Titan Nebula should be unveiled at the beginning of November this year when Pascal Le Du uses the 1-meter C2PU telescope at Calern Observatory, Alpes-Maritimes (France) for spectroscopic measurements.

If confirmed, the Titan Nebula would enter the TOP 3 largest Planetary Nebula ever detected: an extremely rare discovery made possible thanks to a collaboration of three astronomy enthusiasts. What a honorable work!

The team behind the discovery of the Titan Nebula, from left to right: Xavier Strottner, Marcel Drechsler and Dana Patchick

An American-French-German Team

We owe this discovery to Dana Patchick (USA), Xavier Strottner (France) and Marcel Drechsler (Germany), a team of amateur astronomers whose hunting for Planetary Nebulae has been, for many years, their domain of expertise. Dana Patchick is for example considered as the most significant contributor to PN discoveries in the field of amateur astronomy. Xavier Strottner and Marcel Dreschsler are also well accomplished Nebulae hunters since they have created their own catalog of about a hundred unknown nebulae each and have conjointly made up the StDr catalog which counts 140 members, with 16 confirmed Planetary Nebulae and about 15 candidates.  

Among the most notorious Strottner-Drechsler Planetary Nebulae, we can mention StDr 1 from which the collaboration between the French and the German all began.

StDr 1, the first confirmed planetary nebula discovered by Strottner-Drechsler. Credit: Rochus Hess (acquisition) / Marcel Drechsler (Processing)

StDr 137 is also an interesting object since it was first discovered back in 1984 and named EGB9. At that time, this potentially good PN candidate was rapidly rejected. In 2020, the duo Strottner-Drechsler spotted a hidden white dwarf within the nebula and close to a blinding star almost obstructing the view. A spectroscopic measurement then confirmed EGB9 was actually a planetary nebula! After 26 years sleeping as a usual nebula, EGB9 ranked up back to the list of planetary nebulae. This is why the team nicknamed it "The Sleeping Beauty".

EGB9 or StDr 137 is a re-discovery of planetary nebula. Credit: M. Blauensteiner

We cannot end this article without mentioning our editorial board's favorite: StDr 56. This planetary nebula candidate features a flame-like shape with strong H-Alpha emission compared to Oxygen - which are respectively red and blue in the image. If confirmed, StDr 56 would be the first planetary nebula ever discovered in the Triangulum Constellation!

StDr 56, a recently discovered planetary nebula candidate (2020). Credit: Robert Pölzl (acquisition) / Marcel Drechsler (Processing)

 

Astronomy is a fascinating science for its proximity and accessibility. Being an amateur astronomer does not mean you cannot contribute to broadening our knowledge of Astronomy. Using all the resources you can find publicly on the internet, teaming up with other amateur astronomers, astrophotographers and spectroscopy enthusiasts you can start chasing planetary nebulae like Patchick-Strottner-Drechsler team!

Even though artificial lighting is raising concerns about the access to starry sky in urban areas around the world, looking up at the night sky is something that a lot of people still can do. If observing the Milky Way to the naked eye thrills you but does not completely feed your curiosity yet, multiple ways can get you involved into a deeper practice of astronomy without requiring you to being an astrophysicist. Yes, there are multiple ways to collaborate with professional astronomers and in this article, we have just dealt with one.

 

Although the professional telescopes' performances are constantly improving, astronomy remains still to this day an amazing playground for amateur stargazers. What if you also can contribute to an astronomical discovery? This might not only be a dream!