In a finding likened in terms of scale to the discovery of a new continent on Earth, astronomers have stumbled on a previously unseen structure here in the Milky Way - 50,000 light years in size.
At more than 100 degrees across, the structure spans more than half of the sky, from the constellation Virgo to the constellation Grus and may be millions of years old. No one had noticed before because of the so-called diffuse emission -- a fog of gamma rays that appears all over the sky. The emissions are caused by particles moving near the speed of light interacting with light and interstellar gas in the Milky Way.
One possibility includes a particle jet from the supermassive black hole at the galactic center. There is no evidence that the Milky Way's black hole sports 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 central light-years several million years ago.
From end to end, the newly discovered gamma-ray bubbles extend 50,000 light-years, or roughly half of the Milky Way's diameter, as shown in this illustration. Hints of the bubbles' edges were first observed in X-rays (blue) by ROSAT, a Germany-led mission operating in the 1990s. The gamma rays mapped by Fermi (magenta) extend much farther from the galaxy's plane. Photo Credit: NASA/GSFC
