Intriguingly, the gamma-ray signal detected by NASA’s Fermi Gamma-ray Space Telescope is found in a similar direction and with a nearly identical magnitude as another unexplained feature, one produced by some of the most energetic cosmic particles ever detected.
“It is a completely serendipitous discovery. We found a much stronger signal, and in a different part of the sky, than the one we were looking for,” said Dr. Alexander Kashlinsky, a cosmologist at the University of Maryland and NASA’s Goddard Space Flight Center.
Dr. Kashlinsky and his colleagues were searching for a gamma-ray feature related to the Cosmic Microwave Background (CMB), the oldest light in the Universe.
This light originated when the hot, expanding Universe had cooled enough to form the first atoms, an event that released a burst of light that, for the first time, could permeate the cosmos.
Stretched by the subsequent expansion of space over the past 13 billion years, this light was first detected in the form of faint microwaves all over the sky in 1965.
In the 1970s, astronomers realized that the CMB had a so-called dipole structure, which was later measured at high precision by NASA’s COBE mission.
The CMB is about 0.12% hotter, with more microwaves than average, toward the constellation of Leo, and colder by the same amount, with fewer microwaves than average, in the opposite direction.
In order to study the tiny temperature variations within the CMB, this signal must be removed.
Astronomers generally regard the pattern as a result of the motion of our own Solar System relative to the CMB at about 370 km per second (230 miles per second).
This motion will give rise to a dipole signal in the light coming from any astrophysical source, but so far the CMB is the only one that has been precisely measured.
By looking for the pattern in other forms of light, astronomers could confirm or challenge the idea that the dipole is due entirely to our solar system’s motion.
“Such a…
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