Scientists from Stanford and the Department of Energy's SLAC National Accelerator Laboratory have studied the data from NASA's Fermi Gamma-ray Space Telescope for over four years, along with data from other experiments, to create the most thorough portrait of two large bubbles ever created.
They stretch tens of thousands of light-years above and below our galaxy and shine the brightest in energetic gamma rays, according to a paper published in the publication The Astrophysical Journal.
They were found almost four years ago by a team of Harvard led by Douglas Finkbeiner who searched through data from Fermi's main instrument, the Large Area Telescope.
The portrait reveals a number of puzzling features, said Dmitry Malyshev, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology who co-led on the analysis, according to the Journal.
The outlines of the bubbles are sharp, and the bubbles themselves glow in nearly uniform gamma rays over their colossal surfaces. The farthest reaches of the Germi bubbles claim some of the highest energy gamma rays, but there is no discernable cause for them that far from the galaxy.
Though the parts of the bubbles closest to the galactic plane shine in microwaves as well as gamma rays, about two thirds of the way out the microwaves fade and only gamma rays are detectable, according the Journal.
This differs from other galactic bubbles, and also makes the researchers' work that much more challenging, said Malyshev's co-lead, KIPAC postdoctoral researcher Anna Franckowiak.
"Since the Fermi bubbles have no known counterparts in other wavelengths in areas high above the galactic plane, all we have to go on for clues are the gamma rays themselves," she said, according to the Journal.
Soon after the first discovery, theorists jumped in, offering a number of explanations for the bubbles' origins.
For example, they could have been created by huge jets of accelerated matter blasting out from the supermassive black hole at the center of our galaxy.
"There are several models that explain them, but none of the models is perfect," Malyshev said. "The bubbles are rather mysterious."
Franckowiak confirmed that creating the portrait was not easy.
"It's very tricky to model," said Franckowiak. "We had to remove all the foreground gamma-ray emissions from the data before we could clearly see the bubbles."
Franckowiak believes more data is necessary before they can figure out the origin of the bubbles any further.
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