Astronomers using data from NASA’s Fermi Gamma-ray Space Telescope have detected hints of periodic changes in the brightness of a so-called “active” galaxy, whose emissions are powered by a supersized black hole. If confirmed, the discovery would mark the first years-long cyclic gamma-ray emission ever detected from any galaxy, which could provide new insights into physical processes near the black hole.
“Looking at many years of data from Fermi’s Large Area Telescope (LAT), we picked up indications of a roughly two-year-long variation of gamma rays from a galaxy known as PG 1553+113,” said Stefano Ciprini, who coordinates the Fermi team at the Italian Space Agency’s Science Data Center (ASDC) in Rome. “This signal is subtle and has been seen over less than four cycles, so while this is tantalizing we need more observations.”
Supermassive black holes weighing millions of times the Sun’s mass lie at the hearts of most large galaxies, including our own Milky Way. In about 1 percent of these galaxies, the monster black hole radiates billions of times as much energy as the Sun, emission that can vary unpredictably on timescales ranging from minutes to years. Astronomers refer to these as active galaxies.