The Pinwheel Galaxy has areas of straight arms.  The Milky Way might, as well. Image Credit: NASA
The Pinwheel Galaxy has areas of straight arms. The Milky Way might, as well. Image Credit: NASA

milky way

The Milky Way Might Be Square

14 Oct , 2010 by


Just like being stuck inside and not being able to see what the outside of your house looks like, we’re trapped inside the Milky Way galaxy and aren’t able to see its complete structure. Most of us have this vision of a circular, spiral galaxy with gracefully curving spiral arms. Nope, says a group of astronomers from Brazil. The Milky Way might be square. Not like a box, but, in places, the spiral arms are straight rather than curved, giving the Milky Way a distinctly square look. And our solar system sits right on one the straightest parts of an outer arm.

It really IS hip to be square.

The map of the Milky Way has been redrawn several times since the first attempts in the 1950’s using radio telescopes to trace out the spiral arms of our home galaxy. However, the concept of our galaxy having square-ish arms is not so farfetched: we know of the Pinwheel Galaxy, above, that has areas of straight and squared off arms, and a 2008 study using the Very Long Baseline Array found that instead of arms neatly circling the galactic center, the stars mapped traced a more elliptical orbit. But most of the maps of the Milky Way have assumed that the material in our galaxy orbits the center in a circular fashion, so having arms stars that don’t follow this path come as somewhat of a surprise.

Jaques Lepine and his team from the University of Sao Paulo in Brazil wanted to obtain the equivalent of a ”face-on” map of the spiral arms of our Galaxy, so they studied the spectra produced by clouds of carbon monosulphide, a common gas in our galaxy, rather than the usual suspect of ionized hydrogen.

They were able to determine velocity information for 870 regions of the Milky Way which is a larger number than that of previous studies based on classical HII regions, so they’ve created a new map of the galaxy with detail never seen before. “One way to improve the description of the spiral arms is to increase the number of objects used to trace them,” the team writes in their paper.

The distribution of CS sources and maser sources in the galactic plane with the Cepheid stars in orange and the young open clusters in green. The Sun is represented by a yellow dot. Credit: Lepine, et al.

Not only did they find evidence for straight places in the arms, but they also found an additional third arm. A 2008 study by the Spitzer Space Telescope had demoted the number of arms from four to two, but other studies, including an earlier one by Levine have said three. So, yes, there is some uncertainty on the number of arms. The new arm is about 30,000 light years from the galactic core at a longitude of between 80 and 140 degrees. This one is rounded however, “with strong inward curvature.”

“Basically, our results confirm the main aspects of the spiral structure revealed by the studies of HII regions,” said Lepine and his team. “For instance if we move horizontally across the figure, to the right or to the left of the Galactic center, we find roughly 3 spiral arms on each side, like the previous works. There are departures from the pure logarithmic spirals, with segments of arms that are almost straight lines.”

Drawing a map of the Milky Way is a challenging task, since we only have an edge-on view of the galaxy in which we reside. To top it off, it’s full of dust and gas that muck up the view in the visible light spectrum. So, we have to rely on other spectra.

We may not ever know exactly what our galaxy would look like when viewed from other worlds, but we’ll keep trying.

Read the team’s paper: The spiral structure of the Galaxy revealed by CS sources and evidence for the 4:1 resonance, Lepine, et al.

Additional source: Technology Review Blog

By  -        
Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

8 Responses

  1. Jon Hanford says:

    “We may not ever know exactly what our galaxy would look like when viewed from other worlds, but we’ll keep trying.”

    How about we start with a better representative image of a Milky Way lookalike? Seeing as we think the MWG has a central bar (and now, possibly, some straight arm segments), I would nominate NGC 1232: .

    Great story, Nancy.

  2. pink says:

    I might have to stop calling people squares.

  3. Paul Eaton-Jones says:

    In around 500 years We’ve gone from being the centre of the universe to living in a perfectly normal galaxy to living in the squarest place in the cosmos. That’s how ordinary we are. 😉

  4. HeadAroundU says:

    What about tracking of most stars and making a computer simulation?

  5. pink says:

    “squarest place in the cosmos”

  6. jimhenson says:

    my Obvious reasoning for galaxies is that they are not perfect geometrical square shapes. they appear flat in 2-d photos, but approach 3-d sphere shapes if observed over enough time. they should be considered by relativity to be like their constituent parts atoms and stars, undergoing spins, rotations, collisions, and particle exchanges because of their transitory fractal dependent existances. great walls of superclusters appear flat too, but they too with enough time will form nearly spherical shaped super duper clusters ad on to infinity with all sizes of black holes. Even the dark flow black hole at 150 billion light years distance, can be considered spherical, and a fractal particle of dust, when zooming out farther away into space and time. The universe as far as plasma cosmology is concerned, is of an undeterminable age, posibly and probably infinite in age.

  7. Salacious says:

    Surely you mean a cuboid, after all it is a three-dimensional object!

  8. jimhenson says:

    How stupid to have a square galaxy like as if the milky way was made of solid state (s) atoms. Plasma cosmology and Galactic EM Hyperspheres, Electrosynthesis as evidenced by the Space station is an ongoing process in the sun, and supports correct ideas without the imaginary conclusions of the big-bang theory !

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