Using more than 2 million images collected by NASA's orbiting Spitzer Space Telescope, a team of Wisconsin scientists has stitched together a dramatic 360 degree portrait of the Milky Way, providing new details of our galaxy's structure and contents.
The new composite picture, using infrared images gathered over the last decade, was unveiled today (March 20, 2014) at a TED conference in Vancouver. The galactic portrait provides an unprecedented look at the plane of our galaxy, using the infrared imagers aboard Spitzer to cut through the interstellar dust that obscures the view in visible light.
"For the first time, we can actually measure the large-scale structure of the galaxy using stars rather than gas," explains Edward Churchwell, a University of Wisconsin-Madison professor of astronomy whose group compiled the new picture, which looks at a thin slice of the galactic plane. "We've established beyond the shadow of a doubt that our galaxy has a large bar structure that extends halfway out to the sun's orbit. We know more about where the Milky Way's spiral arms are."
Lofted into space in 2003, the Spitzer Space Telescope has far exceeded its planned two-and-a-half-year lifespan. Although limited by the depletion of the liquid helium used to cool its cameras, the telescope remains in heliocentric orbit, gathering a trove of astrophysical data that promises to occupy a new generation of astronomers.
In addition to providing new revelations about galactic structure, the telescope and the images processed by the Wisconsin team have made possible the addition of more than 200 million new objects to the catalog of the Milky Way.
"This gives us some idea about the general distribution of stars in our galaxy, and stars, of course, make up a major component of the baryonic mass of the Milky Way," notes Churchwell, whose group has been collecting and analyzing Spitzer data for more than a decade in a project known as GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire). "That's where the ballgame is.".
The survey conducted by the Wisconsin group has also helped astronomers understand the distribution of the Milky Way's stellar nurseries, regions where massive stars and proto-stars are churned out.
"We can see every star-forming region in the plane of the galaxy," says Robert Benjamin, a professor of physics at the University of Wisconsin-Whitewater and a member of the GLIMPSE team.
"This gives us some idea of the metabolic rate of our galaxy," explains Whitney. "It tells us how many stars are forming each year."
Churchwell notes, too, that while Spitzer is helping astronomers resolve some of the mysteries of the Milky Way, it is adding new cosmological puzzles for scientists to ponder. For example, the infrared data gathered by the GLIMPSE team has revealed that interstellar space is filled with diffuse polycyclic aromatic hydrocarbon gas.
"These are hydrocarbons — very complicated, very heavy molecules with fifty or more carbon atoms," Churchwell says. "They are brightest around regions of star formation but detectable throughout the disk of the Milky Way. They're floating out in the middle of interstellar space where they have no business being. It raises the question of how they were formed. It also tells us carbon may be more abundant than we thought."
The new GLIMPSE composite image will be made widely available to astronomers and planetaria. The data is also the basis for a "citizen science" project, known as the Milky Way Project, where anyone can help scour GLIMPSE images to help identify and map the objects that populate our galaxy.
The data from the survey, Churchwell argues, will keep astronomers busy for many years: "It's still up there. It's still taking data. It's done what we wanted it to do, which is to provide a legacy of data for the astronomical community."
The 20-gigapixel mosaic uses Microsoft's WorldWide Telescope visualization platform. It captures about three percent of our sky, but because it focuses on a band around Earth where the plane of the Milky Way lies, it shows more than half of all the galaxy's stars.
The image, derived primarily from the Galactic Legacy Mid-Plane Survey Extraordinaire project, or GLIMPSE, is online at: http://ift.tt/1ggm3N6
Spitzer, launched into space in 2003 and has spent more than 10 years studying everything from asteroids in our solar system to the most remote galaxies at the edge of the observable universe. In this time, it has spent a total of 4,142 hours (172 days) taking pictures of the disk, or plane, of our Milky Way galaxy in infrared light. This is the first time those images have been stitched together into a single, expansive view.
Our galaxy is a flat spiral disk; our solar system sits in the outer one-third of the Milky Way, in one of its spiral arms. When we look toward the center of our galaxy, we see a crowded, dusty region jam-packed with stars. Visible-light telescopes cannot look as far into this region because the amount of dust increases with distance, blocking visible starlight. Infrared light, however, travels through the dust and allows Spitzer to view past the galaxy's center.
"Spitzer is helping us determine where the edge of the galaxy lies," said Ed Churchwell, co-leader of the GLIMPSE team at the University of Wisconsin-Madison. "We are mapping the placement of the spiral arms and tracing the shape of the galaxy."
Using GLIMPSE data, astronomers have created the most accurate map of the large central bar of stars that marks the center of the galaxy, revealing the Milky Way to be slightly larger than previously thought. GLIMPSE images have also shown a galaxy riddled with bubbles. These bubble structures are cavities around massive stars, which blast wind and radiation into their surroundings.
All together, the data allow scientists to build a more global model of stars, and star formation in the galaxy -- what some call the "pulse" of the Milky Way. Spitzer can see faint stars in the "backcountry" of our galaxy -- the outer, darker regions that went largely unexplored before.
"There are a whole lot more lower-mass stars seen now with Spitzer on a large scale, allowing for a grand study," said Barbara Whitney of the University of Wisconsin-Madison, co-leader of the GLIMPSE team. "Spitzer is sensitive enough to pick these up and light up the entire 'countryside' with star formation."
The Spitzer team previously released an image compilation showing 130 degrees of our galaxy, focused on its hub. The new 360-degree view will guide NASA's upcoming James Webb Space Telescope to the most interesting sites of star-formation, where it will make even more detailed infrared observations.
Some sections of the GLIMPSE mosaic include longer-wavelength data from NASA's Wide-field Infrared Survey Explorer, or WISE, which scanned the whole sky in infrared light.
The GLIMPSE data are also part of a citizen science project, where users can help catalog bubbles and other objects in our Milky Way galaxy. To participate, visit: http://ift.tt/yVQjij
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