New Milky Way arm gives symmetry

Thomas Dame: You have this beautiful bi-symmetric symmetry, like a seesaw, like a butterfly’s wings. That’s the kind of symmetry that the galaxy should have.

That’s astronomer Thomas Dame, talking about our galaxy, the Milky Way. Dame and colleagues at the Harvard Smithsonian Center for Astrophysics found a new spiral arm with 10 million suns’ worth of interstellar gas near the center of our galaxy.

Thomas Dame: This is a rather special arm because it is very close to the bar, which is believed to be near the center of the galaxy, and it matches up with a near-side arm which looks very similar.

Astronomers describe our Milky Way as a barred spiral galaxy, with a central bar-shaped region loosely cradled by spiral arms. What’s more, it appears symmetrical, meaning it looks the same from the top if you were to give it a 180 degree turn. But one of the arms, expanding near the galaxy’s center 10,000 light years from Earth, had no known partner until now.

Thomas Dame: So in fact, trying to understand the bar with only that nearside arm was somewhat like a bird trying to fly with one wing. And now we’ve found the other wing.

Dame combed through radio telescope data taken at the Cerro Tololo Inter-American Observatory in Chile to find the new arm.

Thomas Dame: Well I think it’s a nice step forward. All of the galactic astronomers I’ve talked to are just very pleased about it, because it’s clearly a step forward in our understanding.

Our thanks to:
Thomas Dame
Harvard-Smithsonian Center for Astrophysics
Harvard University
Cambridge, MA