The Fermi Gamma-ray Space Telescope has made a surprising discovery beyond our galaxy, as reported by astronomers analyzing 13 years of data. The unexpected feature, detected in a different part of the sky and with a stronger signal than anticipated, has left scientists intrigued.
Alexander Kashlinsky, a cosmologist at the University of Maryland and NASA’s Goddard Space Flight Center, presented the findings at the American Astronomical Society’s 243rd meeting in New Orleans. The gamma-ray signal, found in a direction similar to another unexplained feature associated with highly energetic cosmic particles, adds to the mystery.
The research team initially sought a gamma-ray feature related to the cosmic microwave background (CMB), the oldest light in the universe. The CMB, originating from the universe’s early moments, exhibits a dipole structure, which astronomers attribute to our solar system’s motion relative to it.
Instead of finding the expected gamma-ray signal related to our solar system’s motion, the scientists discovered a signal ten times stronger than anticipated, located far from the CMB dipole. This unexpected finding, detailed in The Astrophysical Journal Letters, prompts questions about the source of this gamma-ray emission.
To explore the dipole structure further, researchers combined 13 years of data from Fermi’s Large Area Telescope, detecting a gamma-ray dipole in the southern sky, distinct from the CMB’s dipole. The magnitude of this dipole is significantly greater than predicted based on our solar system’s motion.
While not the anticipated result, the scientists suspect a connection between this gamma-ray dipole and a similar feature observed in ultrahigh-energy cosmic rays (UHECRs). The Pierre Auger Observatory in Argentina reported a dipole in UHECR arrival directions since 2017, aligning with the gamma-ray dipole. Both phenomena exhibit comparable magnitudes, suggesting a potential link.
The mystery remains unsolved, and astronomers are challenged to identify the sources responsible for both gamma rays and ultrahigh-energy particles or propose alternative explanations for these unexpected cosmic features. The discovery opens new avenues for exploring the universe’s hidden complexities.
