Our galaxy is relatively quiet compared with active galaxies with brightly glowing cores powered by supermassive central black holes swallowing material and spitting out twin jets of Gamma-ray beams in opposite directions, they said.
Astronomers at the Harvard-Smithsonian Center for Astrophysics using NASA's Fermi space telescope say they've detected two faint Gamma-ray beams, or jets, extending from the center of the Milky Way to a distance of 27,000 light-years above and below the galactic plane.
They are the first such Gamma-ray jets ever found, the center reported Tuesday.
"These faint jets are a ghost or after-image of what existed a million years ago," astronomer Meng Su, lead author of a paper in the Astrophysical Journal, said.
"They strengthen the case for an active galactic nucleus in the Milky Way's relatively recent past," he said.
The jets were produced when plasma streamed out from the galactic center following a corkscrew-like magnetic field that kept it tightly focused into the two beams, astronomers said.
When the central black hole of the Milky Way was last active is unknown, they said.
While a minimum age can be calculated by dividing the jets' 27,000-light-year length by its approximate speed, they may have persisted for much longer.
"These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material," study co-author Douglas Finkbeiner said.