NASA'S Fermi Telescope Discovers Giant Structure In Our Galaxy

The structure spans more than half of the visible sky, from the
constellation Virgo to the constellation Grus, and it may be millions
of years old. A paper about the findings has been accepted for
publication in The Astrophysical Journal.

Finkbeiner and Harvard graduate students Meng Su and Tracy Slatyer
discovered the bubbles by processing publicly available data from
Fermi's Large Area Telescope (LAT). The LAT is the most sensitive and
highest-resolution gamma-ray detector ever launched. Gamma rays are
the highest-energy form of light.

Other astronomers studying gamma rays hadn't detected the bubbles
partly because of a fog of gamma rays that appears throughout the
sky. The fog happens when particles moving near the speed of light
interact with light and interstellar gas in the Milky Way. The LAT
team constantly refines models to uncover new gamma-ray sources
obscured by this so-called diffuse emission. By using various
estimates of the fog, Finkbeiner and his colleagues were able to
isolate it from the LAT data and unveil the giant bubbles.

Scientists now are conducting more analyses to better understand how
the never-before-seen structure was formed. The bubble emissions are
much more energetic than the gamma-ray fog seen elsewhere in the
Milky Way. The bubbles also appear to have well-defined edges. The
structure's shape and emissions suggest it was formed as a result of
a large and relatively rapid energy release -- the source of which
remains a mystery.

One possibility includes a particle jet from the supermassive black
hole at the galactic center. In many other galaxies, astronomers see
fast particle jets powered by matter falling toward a central black
hole. While there is no evidence the Milky Way's black hole has such
a jet today, it may have in the past. The bubbles also may have
formed as a result of gas outflows from a burst of star formation,
perhaps the one that produced many massive star clusters in the Milky
Way's center several million years ago.

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

Hints of the bubbles appear in earlier spacecraft data. X-ray
observations from the German-led Roentgen Satellite suggested subtle
evidence for bubble edges close to the galactic center, or in the
same orientation as the Milky Way. NASA's Wilkinson Microwave
Anisotropy Probe detected an excess of radio signals at the position
of the gamma-ray bubbles.

The Fermi LAT team also revealed Tuesday the instrument's best picture
of the gamma-ray sky, the result of 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, Md.
NASA's Fermi is an astrophysics and particle physics partnership,
developed in collaboration with the U.S. Department of Energy, with
important contributions from academic institutions and partners in
France, Germany, Italy, Japan, Sweden and the United States.

"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."

For more information about Fermi, visit:

http://www.nasa.gov/fermi

Source: NASA

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