Rectifying a 227-Year-Old Error: Stellar-remnant Nebula

This is an on-line version of the article published in the April 2013 edition of Journal of the Royal Astronomical Society of Canada. The official PDF version of this can be found here. The dark blue paragraph was edited out of the published version. I’m including it here to give proper credit.


From 1782 to 1802, William Herschel carried out an extensive deep-sky survey. In his Catalogue of One Thousand New Nebulae and Clusters of Stars, he divided all nebulae into five classes, the fourth class being that of planetary nebula. These are described as “Stars with burs, with milky chevelure, with ƒhort rays, remarkable ƒhapes, &c.” (Herschel, 1786, p. 492). He appears to have linked the nebulae to planets because of their milky appearance—having just made the remarkable discovery of Uranus five years earlier. For the past 227 years, astronomers have continued using this unfortunate and inaccurate term, even though William Huggins showed that planetary nebulae consist of hot gases by analyzing the spectrum of the Cat’s Eye Nebula in 1864.

Since then, astronomers through the centuries have had to include notes such as the following by Balik (2007) whenever they communicate with the public:

The name “planetary nebula” is a misnomer. The name arose over a century ago when early astronomers looking through small and poor-quality telescopes saw these objects as compact, round, green-colored objects that reminded them of the view of Uranus. However, “planetary nebulae” are not made of planets, and no planets are visible within them.

It is [high] time that this error be corrected.

I first encountered the problem with “planetary nebula” in May 2011, when I was teaching astronomy to a Grade 9 science class. While explaining the life cycle of stars to the students, I realized it didn’t make sense to call the glowing cloud of gas expelled at the end of a red giant’s life a planetary nebula, since it had nothing do with planets. After a couple of days of cogitating and poring over different types of nebulae, I coined the phrase “stellar-remnant nebula.”

Stellar-remnant nebula is a more suitable name because

  • it describes the origins of the nebulae more accurately
  • the name parallels that of supernova-remnant nebulae
  • one doesn’t have to immediately explain that it has nothing to do with planets

It is encouraging that the term “stellar remnant” is already associated with planetary nebulae in astronomical literature. For example, in the textbook, An Introduction to the Sun and Stars, Green and Jones state, “[i]t thus seems to be the case that through most of the life of a star, severe mass loss occurs only when a planetary nebula is shed, with the resulting stellar remnant becoming a white dwarf, or when a massive star ends its life as a Type II supernova.” (Green, 2004, p. 129)

Previous use of the term “stellar-remnant nebula”

On January 6, 2013, I created a Wikipedia page for “stellar-remnant nebula” that pointed to “planetary nebula” and then I also added the following bolded text to the entry for planetary nebula: “A planetary nebula, more correctly known as a stellar remnant nebula, is an emission nebula ….” After updating the Wikipedia page for planetary nebula, I realized that a search needed to be done for any prior usage of the term. Employing Google, Yahoo, and Google Books searches, I discovered that this term has only ever been used very few other times, not always correctly.

For example, in a blog posted on 2010 March 23, astrophysics student Philip Stobbart used the term “stellar-remnant nebula” to refer to NGC 7822 (Stobbart, 2010). Alas, NGC 7822 is actually a giant molecular cloud of over 40 light years in diameter that serves as a nursery for new stars to be born (Nemiroff, 2011). The name stellar-remnant nebula is not applicable to this object as it already has a perfectly satisfactory name.

The one and only prior correct use of this term led me down some interesting paths. Searching with Google reveals that the term “stellar remnant nebula” was independently conceived in 2006 by someone with the username Marasama on a now deleted Geocities page. Before the Geocities web hosting service was permanently shut down by Yahoo in 2009, it was mirrored on a site called Oocities, thus the website containing this term is www.oocities.org/marasama . The attribution of this webpage simply says, “Page updated on 3/22/06. If you wish to talk to me, go to the ExtraSolar Vision Forum section and ask for Marasama.” I followed the link to Extrasolar.net; however, the domain no longer exists. With a little sleuthing I was able to find the following: The Internet Archive Wayback machine is only able to show that Extrasolar.net is a list of extrasolar planets. It showed no forum, thus no further information about the user Marasama. Further digging found that Extrasolar.net was set up by the space artist John Whatmough (deceased) and was replaced by Extrasolar Visions II (http://solar-flux.forumandco.com) which does indeed have a moderately active user named Marasama. There is also a Wikipedia user name Marasama whose talk page gives the following information: “My background, I am an armchair astronomer, (probably more laid back)… My degree is in Computer Science, B.S.” Eventually I was able to establish contact with him and found out that his name is James Y. Paul and that he indeed was the first person to invent this term.

Is it unreasonable to expect that the astronomical community will adapt to this new name for planetary nebulae? Other significant corrections have occurred in the past: William Herschel’s original name for Uranus: Georgium Sidus was rejected within eight years of his naming it. Some corrections have taken longer: the reclassification of Pluto occurred 76 years after its discovery in 1930.

Alternative names and Abbreviations

Are there any other names that would be better than stellar-remnant nebulae to describe planetary nebulae? The only one I’ve come across in my research is the suggestion that “ejection nebula” be used instead of planetary nebula (Balick, 2007). However, the term “ejection nebula” is more general than “stellar-remnant nebula” and could be used to describe nebula that are ejected by various processes, rather than those that specifically cause planetary nebulae to form. Thus stellar-remnant nebula remains the more accurate term. The term “ejection nebula” also does not seem to be in common use in astronomical literature: an online search indicated only a few instances of the phrase. A typical example is the paper on the arXiv database entitled Discovery of a Luminous Blue Variable with an Ejection Nebula Near the Quintuplet Cluster (Mauerhan, 2010). The Pistol Nebula, a part of the Quintuplet Cluster, is an emission nebula created by a star so massive and luminous that it is throwing off enough material to create a pistol-shaped arc, which may be why the authors of the above paper are introducing a new category of nebulae.

The final remaining issue is deciding how to abbreviate “stellar-remnant nebula.” Existing related abbreviations are the following (List of Astronomy Acronyms, n.d.):

  • PN   Planetary Nebula
  • SN   Supernova
  • SNe  plural
  • SNR  Supernova remnant (nebula)

Some possible abbreviations along with potential problems that they might have:

  • SR    perhaps not informative enough and can be confused with possible abbreviations the term “stellar remnant”.
  • SRN   too similar to SNR and easy to confuse.
  • STR   (STellar Remnant) existing abbreviation for “street”.
  • SLR   (SteLlar Remnant) existing abbreviation for “Single Lens Reflex” (camera).
  • STN   (STellar remnant Nebula) existing abbreviation for “station.”
  • StRN  (STtellar Remnant Nebula) there are very few mixed case astronomical abbreviations.

It will be left to the astronomy community to decide on which to accept.

Notes

For more information on the history of planetary nebula see

http://www.jenedo.info/histres.html
http://neilenglish.net/planetary-nebulae-through-history/

References:

Balick, B. (2007). Planetary Nebulae and the Future of the Solar System. www.astro.washington.edu/users/balick/WFPC2/

Green, S. F., Jones, M. H., & Burnell, S. J. (2004). An Introduction to the Sun and Stars. Cambridge: Open University.

Herschel, W. (1786). Catalogue of one Thousand New Nebulae and Clusters of Stars. Retrieved from http://archive.org/stream/philtrans06914069/06914069#page/n35/mode/2up

List of Astronomy Acronyms. (n.d.) In Wikipedia. Retrieved January 12, 2013 from http://en.wikipedia.org/wiki/List_of_astronomy_acronyms#S

Mauerhan, J. C., Morris, M. R., Cotera A. S., Dong, H., Wang, Q. D., Stolovy, S. R., Lang, C. C., & Glass, I. S. (2010, February 17). Discovery of a Luminous Blue Variable with an Ejection Nebula Near the Quintuplet Cluster. [arXiv:1002.3379 astro-ph.GA] Retrieved from http://arxiv.org/abs/1002.3379

Nemiroff, R. J. & Bonnell, J. T. (2011). Astronomy Picture of the Day, 2011 November 16. http://apod.nasa.gov/apod/ap111116.html

Stobbart, P. (2010, March 23). Star formation near and far. http://kendalastronomer.wordpress.com/2010/03/23/star-formation-near-and-far/