Monday, July 27, 2009

Whats in a name

Galaxy Zoos so-called Green Pea galaxies

Image Credit: Galaxy Zoo / SDSS

Today, on both the arXiv astro-ph preprint server (where many astronomers post papers accepted for publication in our professional journals) and at Universe Today, articles announced the discovery of "Green Pea" galaxies by researchers analyzing results from the citizen science project Galaxy Zoo. These galaxies are a type of small, compact galaxy rapidly forming stars. They are green in color because of light emission from oxygen, which is very common in star-forming regions. (Many of the Hubble pictures of star-forming clouds in our galaxy have this same greenish glow.) It's a neat discovery; read the Universe Today article or the Galaxy Zoo blog post on these objects.

Alas, I think the name "Green Pea" is too cute to last. Original names for types of astronomical objects do not have a good track record. For example, a type of faint blue galaxy was once called boojums, short for "blue objects observed just undergoing moderate starburst" and based on a creature from the Lewis Carroll poem The Hunting of the Snark. That moniker failed to catch on.

No, we astronomers tend to give things much more boring, though perhaps more scientifically descriptive, names. Spiral galaxies are galaxies that look like spirals. Elliptical galaxies are, well, elliptical. "E+A" galaxies are galaxies that look elliptical ("E") but have spectra indicating the presence of stars of spectral class "A" (which are normally absent in elliptical galaxies). Even slightly fanciful sounding names like "planetary nebulae" just mean nebulae (gas clouds) that look kind of like planets in small telescopes. The more imaginative term "Big Bang" was coined by British astronomer Sir Fred Hoyle on a BBC radio show in 1949; some people claim this was to disparage a theory Hoyle didn't believe, although Hoyle claimed he was just being descriptive. But even this rare piece of originality has detractors; in the comic strip Calvin and Hobbes, Calvin wants to rename the Big Bang the "Horrendous Space Kablooey." (Some astronomers have tried to latch on to this term, but the "Big Bang" is sticking.)

In astronomy, originality in names just isn't appreciated nor adopted. William Herschel wanted to name the planet he discovered Georgium Sidus ("George's Star") after King George III, but the planet eventually became known as Uranus, named after the mythical father of Saturn, who was the father of Jupiter. Of course, that name doesn't permit any schoolchildren to take the planet seriously, so maybe we should have stuck with Herschel's idea.

While the names of specific objects (like planets and stars and galaxies) have to be approved by the International Astronomical Union, names of types of objects do not. The names that get accepted over time tend to be names that are fairly conservative, perhaps because we unconsciously feel that the primary point of the name is to convey a clear picture of the object in question, especially to people who work in different parts of the field. If we stand up in front of a group of astronomers who we don't know and say, "I'm going to talk about Green Pea galaxies," 90% of them won't have any clue what you are talking about, and many of those therefore won't take you seriously. But if you stand up and say, "I'm going to talk about star-forming ultra-compact dwarf galaxies," even astronomers who don't work on galaxies will be able to guess what you are talking about. I'm not saying that this cultural phenomenon is right or fair (see chapter IV of "The Little Prince"); it's the way things are and probably will remain.

So, I fear that Green Pea galaxies are likely doomed to get a boring name like "compact extremely star-forming galaxies" (the subtitle to the green pea paper). More likely, I suspect they'll be known as star-forming ultra-compact dwarf galaxies, since "ultra-compact dwarfs" are an already-accepted type of galaxy (guess what -- ultra-compact dwarf galaxies are small, very compact galaxies), and the Green Peas seem to be related to the UCDs in many ways. This is too bad, as it would be cool to create a computer animation of the in-spiral and merger of two Green Pea galaxies; the paper could be called "Visualizing Whirled Peas".

1 comment:

  1. Thanks and fine with me, but I have no idea where the 'green' came in (it's kind of too obvious huh).. I just named them Peas! ;)

    Hanny van Arkel.