This artist's concept shows the entire sky in gamma rays with magenta circles illustrating the uncertainty in the direction from which more high-energy gamma rays than average seem to be arriving. Photo: Supplied / NASA’s Goddard Space Flight Center
Astronomers have discovered a surprising light "signal" from outside of our galaxy after analysing 13 years of data from NASA's Fermi Gamma-ray Space Telescope.
The powerful telescope detects gamma rays, which are extremely high-energy bursts of light created by violent events like exploding stars and nuclear blasts.
Alexander Kashlinsky - a cosmologist at the University of Maryland and NASA's Goddard Space Flight Centre in Greenbelt - presented an unexpected finding from the observatory at this week's meeting of the American Astronomical Society.
"It is a completely serendipitous discovery," he said at the event in New Orleans.
"We found a much stronger signal, and in a different part of the sky, than the one we were looking for."
The gamma-ray signal was intriguingly found in a similar direction as another unexplained feature produced by some of the most energetic cosmic particles ever detected.
A research paper describing the discovery was published in The Astrophysical Journal Letters on Wednesday.
A quest to understand the 'early universe'
The research team was originally searching for a gamma-ray feature related to the cosmic microwave background (CMB), which is the oldest known light in the universe.
Scientists say the CMB is a relic from when the hot, expanding universe had cooled enough to form the first atoms after the Big Bang.
The subsequent burst of light was stretched by the expansion of the universe over 13 billion years and was first detected in the form of faint microwaves in 1965.
Astronomers in the 1970s discovered the CMB had a "dipole" structure, meaning it has two ends with opposite charges.
The CMB was found to be sightly hotter with more microwaves than average toward the constellation Leo, and colder by the same amount with fewer microwaves than average in the opposite direction.
Scientists generally regard this dipole pattern as a result of the movement of our solar system relative to the CMB.
But the research team hoped to confirm or challenge that idea by studying other forms of light, such as gamma rays, for a similar pattern.
Co-author Fernando Atrio-Barandela, a professor of theoretical physics at the University of Salamanca in Spain, said such a measurement is important.
"A disagreement with the size and direction of the CMB dipole could provide us with a glimpse into physical processes operating in the very early universe, potentially back to when it was less than a trillionth of a second old," he said.
The team combined 13 years of gamma ray data from NASA's Fermi Large Area Telescope to analyse the cosmic gamma ray background.
Co-author Chris Shrader - who is an astrophysicist at the Catholic University of America in Washington and Goddard - said the researchers found a gamma ray dipole, but its peak was located in the southern sky, far from the CMB's.
"Its magnitude is 10 times greater than what we would expect from our motion," he said.
"While it is not what we were looking for, we suspect it may be related to a similar feature reported for the highest-energy cosmic rays."
This similar feature was first observed by the Pierre Auger Observatory in Argentina in 2017.
The observatory discovered a dipole peak of ultra high-energy cosmic rays in a similar location and magnitude to the gamma ray peak.
The researchers suspect the two phenomena are linked and that there is an unidentified source producing both the gamma rays and the ultra high-energy particles.
To solve this cosmic conundrum, astronomers must either locate these mysterious sources or propose alternative explanations for both features.
- This story was first published by the ABC
