Patchwork galaxy

By Phil Plait | August 22, 2011 6:00 am

Sometimes I think it’s a good idea to start off the week with a gorgeous spiral galaxy. So here’s a fantastic example of a flocculent (fluffy or patchy) spiral: NGC 3521 in the constellation of Leo, care of the Very Large Telescope:

[Click to enflocculenate.]

NGC 3521 is a mere 35 million light years away (350 quintillion kilometers, a comfy airplane ride of just 50 trillion years or so; ask for an extra bag of peanuts), which is outside our local area but still close as the Universe goes. It’s half the size of our Milky Way home, about 50,000 light years across. [Note that it has that same effect I mentioned in an earlier post where the dust on the side of the galaxy closer to us appears darker; the light from intervening stars in that galaxy appear to "fill in" the dust on the other side.]

A large fraction of spiral galaxies have these patchy, ill-defined arms, so nature is telling us something: these things are easy to make. Grand design spirals — ones like ours, with splashy well-defined spiral arms — appear to be due to some global effect creating the arms; stars near the galaxy’s center orbit more quickly than ones farther out, so spiral arms should get wound up relative quickly. The fact that so many grand design spirals are seen means that this differential rotation does not destroy the spiral pattern: something most be maintaining it (we think it’s a traffic jam-like effect).

Flocculent spirals, on the other hand (arm?) are more likely to have some sort of local effect in the disk creating the patchiness — if it were some galaxy-spanning effect then we’d see better defined arms! Perhaps regions of local star formation from dense clouds are being stretched and pulled apart by differential rotation, for example, or, rather more likely, combination of several factors working in concert.

But the contrast between the two types of spirals is striking. And the differences between spirals don’t stop there: there are barred spirals, ones with small nuclei, ones with big nuclei, arms that are wound tightly, others loosely… the variety in nature on how to make a colossal structure 500 quadrillion kilometers across containing hundreds of billions of stars is pretty amazing. And we have a long way to go to understanding why they’re different! The math and physics of the behavior of galaxies is fierce, to say the least. They may look fluffy, but the science underlying them is anything but.

Image credit: ESO/O. Maliy

Related posts:

The Milquetoasty Way
The dusty depths of a spectacular spiral galaxy
Setting the bar
The heat of the Pinwheel

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (17)

  1. Jason

    An amazing picture Phil, thanks for sharing.

    and just what does fluffy science look like?

    Star trek is often referred to as rubber science, but I am nost sure what fluffy science is..

  2. OtherRob

    “Flocculent” is one of those words that just sounds dirty, even if it isn’t. :)

  3. Jay

    Obviously, you just need one of these:
    big enough to fit a galaxy inside.

  4. verbatim

    Beautiful! But be careful with the “grand design” designation. Rick Perry will getcha!

  5. Checkmate1

    ” Stars near the galactic center orbit more quickly than ones farther out ”

    Actually, Louise Volders might disagree…( see Galaxy Rotation Curve, Wikipedia etc.) as might several others. Isn’t this one of the arguments put forth in support of Dark Matter?

  6. Cynthia

    Cinnamon toast crunch.

  7. TMB

    @4 Checkmate1: Although he wasn’t specific, I’m pretty sure he means that the angular speed is higher. If physical speed rises proportional to radius within the galaxy, angular speed is constant (and is called “solid body rotation”, since it is how solid bodies rotate – although it doesn’t imply that it is actually a single solid!). But if physical speed doesn’t rise quite as rapidly, then the angular speed falls with radius, and you get winding as described.

  8. jess tauber

    Two questions: a) how small is the smallest ‘grand design’ spiral? and b) how big is the biggest ‘flocculent’ spiral?? Just want to get some bearings on the overlap. Thanks.

  9. QuietDesperation

    Click to enflocculenate

    OK, I’m calling for an intervention.

  10. Randy

    Another ‘miss’ by Messier? One of my favorite non-Messier galaxies. This Hubble image has been my computer desktop since January:

  11. Eric

    *chuckle* Is it bad that what sticks in mind is the very amusingly blunt name of the Very Large Telescope? Yes, I read the site describing it. I still find the name amusing. But that’s me. I mean, what if they build a bigger array? Is it the Even Bigger But Not Yet Gargantuan Telescope? Maybe the Really Big And We Mean It This Time Telescope?


    Regardless, gorgeous image and, as always, interesting information.

  12. Steve

    “ask for an extra bag of peanuts”

    And some lemon soaked napkins and a piece of fairy cake while you’re at it.

  13. Jon Hanford

    Flocculent arms aside, NGC 3521 also displays tidal tails indicative of a recent merger with a smaller companion galaxy. Extensions are particularly prominent adjacent to the ansae of the galaxy, as seen in these two images:
    [Dean Rowe]
    [Mischa Schirmer]

  14. Messier Tidy Upper

    Beautiful. :-)

    Great write up too. :-)

    Great way to start the week – except that’s yesterday in my timezone it’s midday Tuesday now. ūüėČ

  15. Messier Tidy Upper

    @ ^ Not that I’m complaining. The BA can post these marvellously splendid & splendidly marvellous wonder-filled galaxy images any day of the week – anytime at all – as far as I’m concerned! ūüėČ ūüėÄ

  16. TMB

    @11: ESO (who run the VLT) have a new project that is currently called the E-ELT for European Extremely Large Telescope. This was the scoped down version of the original idea, OWL for OverWhelmingly Large telescope.

    No, I’m not making any of that up.

  17. matt

    I also thought the leading theory was that dark matter was maintaining spiral arms, not the traffic jam effect. Doesn’t the effect of dark matter fix the winding up problem?


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