A newly-discovered structure, which spans 50,000 light-years and is positioned in the center of the Milky Way, was identified by NASA's Fermi Gamma-ray Space Telescope. 

Doug Finkbeiner, founder of the new structure and an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., has discovered two gamma-ray-emitting bubbles that may be millions of years old and span from the constellation Virgo to the constellation Grus. He was able to find these bubbles using NASA's Fermi Gamma-ray Space Telescope, which is a space observatory, and astrophysics/particle physics partnership developed in collaboration with the U.S. Department of Energy. 

"What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center," said Finkbeiner. "We don't fully understand their nature or origin." 

While hints of the bubbles were visible in earlier spacecraft data, astronomers conducting previous studies on gamma rays were unable to find the bubbles mainly because of the fog which surrounds gamma rays throughout the sky. When particles, which are moving at the speed of light, react with light and interstellar gas in the Milky Way, a fog develops. 

Finkbeiner and his team were able to find the gamma-ray-emitting bubbles by processing available data from Fermi's Large Area Telescope (LAT), which is a high-resolution and extremely sensitive gamma-ray detector. Researchers continuously refined models in an effort to identify new gamma-ray structures hidden by the fog. Finkbeiner was able to isolate the fog from the LAT data by using different estimates of the fog in these models, and finally stumbled upon the large bubbles. 

"Since its launch in June 2008, Fermi repeatedly has proven itself to be a frontier facility, giving us new insights ranging from the nature of space-time to the first observations of a gamma-ray nova," said Jon Morse, Astrophysics Division director at NASA Headquarters in Washington. "These latest discoveries continue to demonstrate Fermi's outstanding performance."

The next step is to figure out how these bubbles were formed. The gamma-ray-emitting bubbles have "well-defined" edges and their emissions are much more energetic than any other gamma-ray fog previously found in the Milky Way, which, according to researchers, suggests that the bubbles were formed as a result of large and somewhat fast energy release. Finkbeiner and his team are unsure as to what the source of this energy release was, but hypothesize that it may be a particle jet from the supermassive black hole located at the galactic center. There is no evidence that the Milky Way's black hole has these fast particle jets, but there's a possibility it may have in the past. Another possible source of the energy release may be gas outflows from a burst of star formation.

"In other galaxies, we see that starbursts can drive enormous gas outflows," David Spergel, a scientist at Princeton University. "Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics."

In addition to discovering the gamma-ray-emitting bubbles, the team also revealed Fermi's best picture of the gamma-ray sky on Tuesday. They were able to produce such an image after two years of data collection. 

"Fermi scans the entire sky every three hours, and as the mission continues and our exposure deepens, we see the extreme universe in progressively greater detail," said Julie McEnery, Fermi project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.