The Blazar Light Cycle Confirmed by NASA's Fermi Mission

A two-year cycle in the gamma brightness of a blazar, a galaxy powered by a supermassive black hole, has been confirmed by ten years of observations at NASA's Fermi Gamma space telescope. The results were announced today at the eighth meeting of the Fermi International Symposium this week in Baltimore.

"This is the first time that a gamma ray period is confirmed in an active galaxy," said Stefano Ciprini, researcher at INFN Division Tor Vergata of the Agency's Space Science Data Center. Italian space in Rome. "The period of gamma rays is also visible in other frequency bands, including visible light, and other X-ray and radio data suggest similar brightness spikes."

Part of the material falling into the blazar, called PG 1553 + 113, forms a particle stream that emits gamma rays, the highest energy light form, almost directly to the Earth.

"This result was achieved after 10 years of continuous monitoring by Fermi's Large Area Telescope (LAT)," said Sara Cutini, researcher at the Italian Institute of Nuclear Physics (INFN) in Perugia. "We first saw an index of periodic modulation in 2014, when we produced detailed analyzes of LAT data, and we can now say for sure that this long-term behavior is real."

A pair of supermassive black holes in the heart of the blazar is the most enticing option. In this scenario, one of the supermassive black holes would emit gamma rays from a jet and the direction of this jet would "flicker" due to interactions with its black hole. This would make the PG 1553 + 113 a prime target for a future space-based gravitational wave detector, such as the Agency's Laser Interferometer Spatial Antenna (LISA). European space, which should be launched in the 2030s, or Square Kilometer Array (SKA). , a giant radio telescope under construction in South Africa and Australia.

Scientists warn that other interpretations can explain cyclical emissions. For example, a disk of material swirling around a single supermassive black hole may exhibit periodic instabilities or general relativistic effects causing the jet emitting gamma rays to precede.

"The periodic variations of visible light, collected over 12 years by optical telescopes on Earth and in space, are similar and well correlated with what we see in the high-energy gamma-ray telescope of Fermi: This is a totally new discovery for high energy gamma ray blazars and active galaxies, "said Stefan Larsson, a researcher at Stockholm's Royal Institute of Technology, in a statement. Sweden.

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For more information on NASA's Fermi mission, visit www.nasa.gov/fermi