10-year observation of NASA's Space Telescope Fermi was able to confirm the presence of a 2-year brightness cycle in the blazar gamma radiation. This is a galaxy activated by a supermassive black hole. This is the first case of a similar confirmation of the gamma period. The period of gamma radiation is also observed in other wave bands, among which is visible light, and additional x-ray and radio data indicate similar brightness peaks.
Part of the substance entering the blazar PG 1553 + 113 forms a jet of particles that release gamma rays. This is the highest energy of light, directed almost directly to the Earth. This result was achieved due to 10 years of continuous monitoring at the Fermi LAT telescope. At first, scientists saw a hint of periodic modulation in 2014, when they prepared a detailed analysis of the data. Now the team confidently states that long-term behavior is real. A pair of supermassive black holes in the heart of Blazar is the most tempting opportunity. In this case, one of them will emit gamma rays in a jet, whose direction “swells” due to contact with a nearby black hole. This would make PG 1553 + 113 a future target for a space gravitational detector, such as an ESA LISA laser interferometer to be launched in the 2030s, or the giant SKA radio telescope, which is being built in South Africa and Australia.
Scientists do not deny that there may be other interpretations that will explain cyclical emission. For example, periodic instabilities can exist in a disk of matter circulating around a single supermassive black hole, or else we are talking about general relativistic effects leading to gamma radiation precession