Research published in The Astrophysical Journal identifies a way to detect periodic gamma-ray emissions from 11 active galaxies. The paper is entitled "Systematic search for gamma-ray periodicity in active galactic nuclei detected by the Fermi Large Area Telescope" and provides insight for identifying galaxies with two black holes, instead of the conventionally known galaxies that host a singular black hole at their center.
"In general, supermassive black holes are characterized by masses of more than a million masses of that of our sun," said lead author Pablo Peñil, a Ph.D. student at Universidad Complutense de Madrid in Spain. "Some of these supermassive black holes, known as active galactic nuclei (AGN) have been found to accelerate particles to near the speed of light in collimated beams called jets. The emission from these jets is detected throughout the entire electromagnetic spectrum, but most of their energy is released in the form of gamma rays."
What are gamma rays? In short, they are the shortest wavelength electromagnetic waves and their unpredictability make it difficult to monitor their patterns. Watch the video below to learn more about gamma rays.
Nevertheless, using observations from the Large Area Telescope onboard NASA's Fermi Gamma-ray Space Telescope, this international team has been able to detect the repetition of gamma-ray signals over cycles of a few years, repeating roughly every two years on average.
"Our study represents the most complete work to date on the search for periodicity in gamma rays, a study that will be instrumental in deriving insights about the origin of this peculiar behavior," said co-author Alberto Domínguez. "We have used nine years of continuous LAT all-sky observations. Among the more than two thousand AGN analyzed, only about a dozen stand out for this intriguing cyclical emission."
While the researchers were able to identify galaxies that emit periodic gamma rays, they say they still need to figure out what causes such periodic behavior in order to better understand the way galaxies are formed.
"Previously only two blazars were known to show periodic changes in their gamma-ray brightness. Thanks to our study, we can confidently say that this behavior is present in 11 other sources," said co-author Sara Buson, a professor at the University of Würzburg in Germany. "In addition, our study found 13 other galaxies with hints of cyclical emission. But to confidently confirm this, we need to wait for Fermi-LAT to collect even more data."