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 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, scientists said.

Known as GLIMPSE360, the interactive Milky Way portrait allows viewers to 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 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.

Thousands of sparkling young stars nestled within the giant nebula NGC 3603. This stellar "jewel box" is one of the most massive young star clusters in the Milky Way Galaxy. NGC 3603 is a prominent star-forming region in the Carina spiral arm of the Milky Way, about 20,000 light-years away. This image shows a young star cluster surrounded by a vast region of dust and gas. The image reveals stages in the life cycle of stars. The nebula was first discovered by Sir John Herschel in 1834. The image spans roughly 17 light-years. (NASA/MCT)

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 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.