Huge Milky Way portrait reveals new details

MILWAUKEE — A team of Wisconsin scientists has stitched together a dramatic 360-degree portrait of the Milky Way that reveals never-seen-before details of our galaxy.

The new galactic portrait, www.spitzer.caltech.edu/glimpse360, is made up of about 2.5 million infrared images collected by NASA’s orbiting Spitzer Space Telescope over the last decade.

By looking at the sky in infrared light, astronomers can cut through clouds of obscuring interstellar dust, revealing stars, previously hidden stellar nurseries, proto stars, bubbles, jets, bow shocks, and nebulae that can’t be seen in visible light.

The infrared images that make up the new portrait provide revelations about the Milky Way’s content and structure. They add more than 200 million new stars to the catalog of the Milky Way — plenty of astrophysical data to occupy a new generation of astronomers, according to scientists involved with the research.

Known as GLIMPSE360, the interactive Milky Way portrait was unveiled Thursday on a large visualization wall installed by Microsoft at a conference in Vancouver, but it will be made widely available to astronomers and planateria planeteria. Viewers can actually look through the plane of the galaxy and zero in on specific objects with a zoom feature.

Scientists can now clearly examine the structure of the Milky Way — how many spiral arms it has, where they are and how far out they extend, said Edward Churchwell, a University of Wisconsin, Madison professor emeritus of astronomy who was involved in compiling the new picture, which shows a 2-degree-wide band of the galactic plane.

The infrared images provide conclusive evidence that a large bar structure consisting of millions of stars runs like a straight line through the center of the Milky Way and extends out to about 12,000 to 13,000 light years from the galaxy’s center. The bar is oriented about 45 degrees to the line joining the sun and the center of the Milky Way, Churchwell said.

For the first time, astronomers also can now measure the large-scale structure of the galaxy using stars rather than gas, Churchwell said.

“We can see stars being born. And if we can identify stars in the process of forming, we can start to learn about the physics of how stars are formed. We don’t really understand the details of how stars are born.”

The distribution of the Milky Way’s stellar nurseries — regions where massive stars and proto stars are churned out — also may be better understood, thanks to the telescope and its images.

“We can see every star-forming region in the plane of the galaxy,” said Robert Benjamin, a professor of physics at the University of Wisconsin,Whitewater and a member of the GLIMPSE team.

The composite gives scientists some idea of the metabolic rate of the Milky Way, said UW-Madison astronomer Barb Whitney, one of the leaders of the GLIMPSE team. “It tells us how many stars are forming each year.”

The general distribution of stars in the galaxy also is now visible. Stars, Churchwell noted, make up a major component of the baryonic mass of the Milky Way.

The 360-degree portrait will help astronomers gain a deeper understanding of the dust that lies between the stars and us, Churchwell said.

But the portrait also uncovers new puzzles to be solved. The infrared data, for example, revealed that interstellar space is filled with diffuse polycyclic aromatic hydrocarbon gas.

“These are hydrocarbons, very complicated, very heavy molecules with 50 or more carbon atoms,” Churchwell said.

“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.”

Sent into space in 2003, the Spitzer Space Telescope has far exceeded its planned 2?½-year lifespan. The telescope remains in heliocentric orbit, gathering astrophysical data, though it is limited by the depletion of the liquid helium used to cool its cameras.

More than 600 research papers already have been published using the data from the infrared galactic survey, Churchwell said.

He figures that the data will keep astronomers busy for many years.

“It’s still up there,” Churchwell said. “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.”

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