Astronomers detect unexplained signal coming from another galaxy

During the analysis of data from the Fermi Gamma-ray Space Telescope over the past 13 years, NASA astronomers have discovered an unexpected signal emanating from beyond our galaxy, the origin of which they cannot explain. Francis Reddy of NASA's Goddard Space Flight Center referred to this phenomenon as an "unexpected and as-yet-unexplained feature beyond our galaxy."

The Fermi telescope observes gamma-ray emissions resulting from powerful energy outbursts, such as supernova explosions. Scientists were studying the data obtained by the telescope to gather more information about the so-called relic radiation, also known as cosmic microwave background radiation. Typically, relic radiation has a dipole structure, with one side hotter than the other. Astronomers believe this occurs due to the motion of the solar system.

Instead of the expected relic radiation structure, researchers discovered a signal containing some of the most energetically powerful cosmic particles ever detected. "This is a completely serendipitous discovery," says Alexander Kashlinsky, a cosmologist from the University of Maryland and NASA's Goddard Space Flight Center. "We found a much stronger signal in a different part of the sky than what we were looking for."

This week, a paper describing the results was published in The Astrophysical Journal Letters. "We found a gamma-ray dipole, but its peak is located in the southern sky, far from the relic radiation, and its magnitude exceeds what we expected by a factor of 10," stated NASA astrophysicist Chris Shrader.

Scientists believe that the observed phenomenon is related to similar cosmic gamma-ray radiation detected by the Pierre Auger Observatory in Argentina in 2017. Astronomers think that these two phenomena may have a common origin, considering their similar structures. They hope to further identify the mysterious source or develop alternative explanations for both features.

NASA's unexpected discovery may assist astronomers in confirming or refuting ideas about how the dipole structure of relic radiation is formed. "The mismatch in the sizes and directions of the relic radiation dipole could give us an opportunity to glimpse into the physical processes occurring in the very early Universe, possibly during times when its age was less than a trillion seconds," believes one of the study's authors, Fernando Atrio-Barandela.