How Galaxies Choose to Relax is Their Own Damn Business

By Julianne Dalcanton | March 7, 2007 1:42 pm

Chad at Uncertain Principles raises the issue of unfortunate names in physics and astronomy. I agree that “strange” and “charm” and “bra” and “ket” are on the cutesy side, but astronomical nomenclature has got to be worse. A fair bit of it is just awkward (for example, in a young star formation region, you’ll often find both molecular hydrogen, which is H2, and ionized hydrogen which is also known as “H-two”, i.e. “HII”, where the II is the roman numeral two). Other terms are historical anachronisms (“planetary nebulae” have nothing to do with planets, but they looked sort of like them through the earliest telescopes). However, to the astronomer teaching large introductory courses (which is most of us), astronomical lingo is downright perilous.

Case in point: The spheroidal distribution of stars in the centers of rotating disk galaxies is called the “bulge”. Now, introduce a bunch of bored and horny 19 year olds into the mix, and you have a dangerous cocktail. One of my colleagues lost complete control of a 250 person lecture class when she had two male students hold up pictures of different galaxies, while she expounded on how “This guy over here has a small bulge, but the bulge of this guy is quite prominent.” The titters started as she forged ahead unknowing, until the entire class collapsed in hysterics. At that point, you just have to put down your laser pointer, send the class home, and head for the bar. Learning is over.

While not quite as extreme, I’ve always been fond of “violent relaxation“, originally coined by Donald Lynden-Bell . The relaxation bit refers to a gravitationally bound system (like a galaxy) coming to its final equilibrium state, and the violent part refers to the fact that this process is not slow and steady, but is usually characterized by rapid changes in the gravitational potential. Broken down like that, it’s not as nuts as you’d initially think, but it’s never going to sound PG.

CATEGORIZED UNDER: Miscellany, Words
  • John

    Hee hee…a similar thing happened to me a couple weeks ago, when, teaching about fluid mechanics and the Bernoulli equation, I declared that the “fluid flow rate depends on the total head” in the system. I turned bright red…

  • Paolo Amoroso

    Along the same line, never mention the name of the 21st moon of Uranus (Trinculo) in Italy — ever. Especially in front of a bunch of bored and horny 19 year olds. Don’t ask.

  • Brad

    “galaxy harassment” goes over well in the intro classes too. Especially when you explain it using terms like “tickling”.

  • George Musser

    There’s something so beautiful, so zeitgeisty, about “violent relaxation”. What better describes going to the gym, swimming laps, or any of the other activities that pass for leisure in modern society?


  • The AstroDyke

    Julianne et al., I have to ask — what do you think about the jargon “wet mergers” and “dry mergers”? (Background: “dry mergers” involve galaxies with stars and dark matter, but very little gas; “wet mergers” involve galaxies that have gas, too.)

    My picky side is bothered by the inaccuracy (“It’s gas, folks, not water, even if we do call it hydrodynamics.”); the phrases “gas-rich” and “gas-poor” mergers seem clearer and less jargony to me.

    Plus, it’s a bit odd, on the border with Creepy, at a meeting to have hundreds of astronomers nattering on about the relative lubrication of their mergers…

  • Adam S

    In my undergrad quantum corse, the prof taught us about stimulated emission. It was early in the morning, though, and we were all half-asleep, so I’m not sure if anyone actually picked up on it until after he said “don’t laugh.”

  • Julianne

    to have hundreds of astronomers nattering on about the relative lubrication of their mergers…

    Ew! I can’t even think about this.

  • The AstroDyke

    Julianne– so it isn’t just me that thought “EEK!” that’s reassuring.

    Even worse for sheer awkward terminology: The CIII emission line is made by the C+2 atom. Or at least, that’s what Gary Ferland says, though few follow the convention. In this case, the lines were named before electrons were discovered — all the spectroscopists knew was, that when you heat the gas, you get different lines….

    Do biologists & chemists put up with such antiquated jargon, too? If not, what’s their secret for deciding on name changes? An add in the paper? “‘Planetary Nebulae’ will henceforth be known as ‘AGN Star Nebulae’. Please make note of it.”

  • Haludza

    lol you said ‘bulge’

  • Sean

    Not one Uranus joke yet? Our commenters are more mature than I imagined.

  • Analyzer

    The CIII emission line is made by the C+2 atom. Or at least, that’s what Gary Ferland says, though few follow the convention.

    Few follow the convention?! Everyone follows the convention. The Roman numeral is always one greater than the ionization.

  • Julianne

    The Roman numeral is always one greater than the ionization.

    Which is also why “HII” is singly ionized Hydrogen.

  • loonunit

    Does it make me a bad feminist if I’m one of the people in the audience who thinks it’s funny when the dry merger discussion leads to the inevitable outcome?

    And I suppose “fluid” mergers aren’t much better?

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  • Douglas

    Julianne, I have to give it to you: you always add the spice of explicit sexuality to this blog.

  • Doug

    Hairy black holes are pretty fun too.

  • Sean

    This blog could use some sexying-up, in my opinion.

    But Mark made me promise I wouldn’t share any of those stories he told me.

  • Julianne

    If Cosmic Variance is responsible for bringing sexy back, then we all are in big, big trouble.

  • Jesse

    Magnetic Confinement Fusion seems to be stuck on food names- Banana orbits, sausage instabilities, kidney bean profiles, etc.

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  • Yvette

    “I’ve been reading about the beginning of the universe. They call it ‘The Big Bang’. Isn’t it weird how scientists can imagine all the matter of the universe exploding out of a dot smaller than the head of a pin, but they can’t come up with a more evocative name for it than ‘the Big Bang’? That’s the whole problem with science. You’ve got a bunch of empiricists trying to describe things of unimaginable wonder.”
    “What would you call the creation of the universe?”
    “The horrendous space kablooie!”

    I’m amazed a discussion of scientific nomenclature got so far without someone bringing that up… 😉

  • Quasar9

    Well Julianne, as galaxies go
    The Sombrero Galaxy has everything
    It could be a glowing halo
    It could be an Etermity Ring, except we know nothing in The Universe is eternal, except perhaps the universe itself (or that from which it proceeded).

    It could be the place some men would want to plunge into head first (the place whence they came from), the place of mystery, untold wonders & de-light

    If the galaxy is female it could be The bulge means that it is pregnant
    If the galaxy is male The bulge could simply means it drinks a lot of bubbles (CO2 from beer or coke) …
    or maybe the bulge indicates the galaxy is indeeed happy to see U.

  • PK

    I remember shuffling and giggling in the lecture theater when our prof introduced the penetration depth.

  • ashamed of myself

    Somehow, during the late nights studying quantum mechanics with fellow graduate students, the Lippmann-Schwinger equation turned into the Lick-My-Dinger equation (say “my” with a southern accent: “mah”). I don’t know how that happened, but I can’t get it out of my mind.

  • Risa

    AstroDyke, I totally agree, despite being friends with the person who introduced this terminology. Even worse is when people go so far as to call their sort-of gas-rich mergers “moist”, a word which really should be banned from polite conversation.

    Sean, I’ll be happy to bring it up and lower the discourse. In the stairwell outside my door in LASR, there was, among other posters of heavenly bodies, one that says “Explore Uranus”. Even after seeing it every day for 3 years, it never failed to crack me up on my way in to work.

  • Peter Erwin

    Magnetic Confinement Fusion seems to be stuck on food names- Banana orbits, sausage instabilities, kidney bean profiles, etc.

    Galaxy dynamics has its share of fun names. Box and tube orbits are a bit utilitarian, but there are banana (and anti-banana) orbits, and pretzel orbits, and fish orbits…

  • David

    The first talk I had to give in a grad astro course was on “ram pressure stripping.” My title page was interesting, though it’s a shame I can’t draw better.

    And then I gave a talk on the high helium sequence of Omega Cen. I started thinking about this high sequence, and on one slide I used the words “joint,” “blunt,” “chronic,” and “weed” (as in “this is a chronic difficulty, how to weed out the contamination”). Nobody noticed until I pointed it out… I was so sad.

  • John Phillips

    I have nothing to contribute to the subject at hand except to enjoy the various contributions. Add to it a post on Korea’s version of Asimov’s Three Laws of Robotics followed by New Mexico legislating Pluto still a planet and this blog really does live up to the title Cosmic Variance as well as raising a smile and a chuckle on a grey Friday morning here in the UK. Long may you continue :)

  • stand

    Speaking of astro-nomenclature, I always enjoy the humor that non-astronomer scientists, especially chemists, get from the fact that astronomers divide the matter constituents of the universe into Hydrogen, Helium and Metals.

  • Amara

    Mmm, the physics field is _full_ of provocative words; it’s hard _not_ to laugh sometimes.

    Once many years ago, I found myself caught in a bit of physics and chess word play in email with someone that I barely knew. I don’t remember which one of us started it, but I think I never laughed as hard in an email conversation as I did with that particular person. Take a look at what you can do with the physics terms.


    (A provocative chess game in progress here ……)

    Do you see that, in this suuuuuuubtle chess game, you are forcing me to ask to your magnetic field to induce MY electric field ?

    Check. :-)

    You could place your piece in a reference frame where my forces are no longer valid.

    You could place your piece in a static magnetic field and let MY moving current loop induce YOUR electromotive force.

    You could forfeit the game, and we could alternate the induction.

    I’ll stop here and let your imaginations fly…. Happy Friday!

  • Stephen Uitti

    In addition to head, mechanical engineers talk about male and female parts of various fasteners, which have obvious visualizations. The list goes on and on, though it’s been awhile since i was in school.

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