Learning More about the Home Galaxy

Wow. I miss ONE AAS meeting, and they lose two spiral arms from our galaxy! This is what I get for staying home and working on two big projects with massive deadlines. I did manage to log in and watch the press conferences from the comfort of my overstuffed office, so I caught the gist of what has turned out to be a very cool story.

First, some background. For years, astronomers thought our galaxy probably had four spiral arms. But, it’s hard to tell because we can’t exactly SEE all of our galaxy in visible wavelengths. This is due to all the dust in the galactic plane, and since WE’RE in the galactic plane, it’s like trying to see through a dense fog when it comes to looking in various directions. Isaac Asimov put it best when he wrote, “In a sense, we are on a low roof on the outskirts of the city on a foggy day.”

Well, as it turns out, telescopes with infrared capability can look through that fog and see farther and sharper than visible-light counterparts. So, it makes sense to use such facilities when you want to see what’s out there.

Groups of astronomers from JPL/CalTech and the University of Wisconsin used the infrared-enabled Spitzer Space Telescope to look at the galaxy. Their survey, called the Galactic Legacy Infrared Midplane Extraordinaire (GLIMPSE), spanned 130 degrees in longitude (65 degrees on either side of the center of the galaxy), and 2-4 degrees in latitude. Since Earth is located about halfway out along the plane of a flattened spiral, this survey actually encompasses a large fraction of the volume of the Milky Way. The infrared views (shown below) show where the stars are, as well as the dust clouds in the plane, allowing a more complete star census to be done.

Here’s one of two views of the Milky Way from GLIMPSE, emphasizing wavelengths (3.6 – 8 microns) in the familiar blue-green-red that our eyes see, with the shortest wavelengths displayed in blue and the longest in red. For more technical details, check out the GLIMPSE page at the University of Wisconsin’s team site. They also have downloadable poster-size files of this and another view of the same data.

Now, if you could turn that image so we could see it from the “top down” this “artist’s concept” might be what our Milky Way really looks like. The survey showed, for the first time, that arms we thought were there, really aren’t. The Milky Way’s elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars.

Spitzer’s imagery of the galaxy comprises 800,000 snapshots, and when you piece them all together, they make the clearest view of the Milky Way ever produced. The team has created a poster that they showed at AAS that is 180 feet (289 meters) long and 3.5 feet (2.1 meters) wide. The poster is going on tour soon, apparently showing up at Griffith Observatory (where they have a similar large-scale image of a small part of the Virgo Cluster called “The Big Picture” on display), and then on to various other cities. You, however, can explore it from the comfort and privacy of your home or office by going to http://mipsgal.ipac.caltech.edu/p_map.html where they have a GoogleMaps zoomable map. Check it out!