Our 10 billion year-old Milky Way galaxy seemingly gets more complicated with each passing observation.
That’s partly because trying to observe its structure — from our vantage point two-thirds of the way out from the galactic center, at least — is akin to determining the boundaries of a thickly-populated old growth forest from one isolated ground-level spot.
But that’s exactly what the just-completed GLIMPSE (Galactic Legacy Infrared Mid-Plane Extraordinaire) ten-year survey has done from NASA’s earth-trailing Spitzer Space Telescope.
The idea behind GLIMPSE was to do a deep panorama of our galaxy in the mid-infrared and to penetrate our galaxy’s dark molecular clouds where at least some of our Milky Way’s estimated 400 billion stars are actually still forming.
Astronomers are still in the process of analyzing the data on the survey, with results expected by mid-summer. But for a preview, Forbes.com turned to Ed Churchwell, a GLIMPSE Principal Investigator and an astronomer at the University of Wisconsin-Madison, who has been studying the Milky Way for almost a half century.
What has GLIMPSE taught us about the plane of our galaxy?
That it’s full of hot bubbles of gas around really hot luminous stars. Due to both their bright radiation and particles, these stars have blown bubbles around themselves. That tells us a lot about the evolution and impact of these stars on the galaxy and has opened a whole new field of research.
What have you learned about the structure of the galaxy itself?
We’ve found that our galaxy has a fairly long bar that goes right through its center and reaches about halfway out to the sun but is tilted about 45 degrees [from the sun-galactic center direction]. As a result, the galaxy looks very lopsided. And we see a lot more stars in the Northern part of our galaxy than the South.
What’s the bar’s composition?
This bar is about 13,000 light years in radius and primarily detected by an old population of very numerous “Red Clump Giant” M-spectral type stars in the latter stages of their evolution. These giants have a well-determined luminosity, which makes them useful as standard galactic candles. So, we’re able to determine the large scale structure of our galaxy.
So, our galaxy is now officially classified as a barred grand spiral?
That’s right, with what appear to be two major arms, the Perseus arm and the Carina-Scutum arm. We have three smaller, less prominent arms, Sagittarius, Norma and the Outer arm. And there are also two minor arms near the galactic center, the Far 3kpc arm and the Near 3kpc arm, as well as our local Orion spur.
- Page 1 / 2