2024-01-14 23:55:19
Astronomers analyzing 13 years of data from NASA’s Fermi Gamma-ray Space Telescope have found an unexpected and still unexplained feature outside the galaxy.
“It’s a completely serendipitous discovery,” said Alexander Kashlinsky, a cosmologist at the University of Maryland and NASA’s Goddard Center. “We found a much stronger signal and in a different part of the sky than what we were looking for.”
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 appear to arrive | Photo: NASA
The team was looking for a gamma-ray feature related to the CMB (cosmic microwave background), the oldest light in the universe. Scientists say the CMB originated when the hot, expanding universe cooled enough to form the first atoms, an event that released a burst of light that, for the first time, might permeate the cosmos. Magnified by the subsequent expansion of space over the past 13 billion years, this light was first detected in the form of faint microwaves across the sky in 1965.
In the 1970s, astronomers realized that the CMB had a so-called dipole structure, which was later measured with high precision by NASA’s COBE (Cosmic Background Explorer) mission. The CMB is regarding 0.12% 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.
To study small temperature variations within the CMB, this signal must be removed. Astronomers generally consider the pattern to be the result of the solar system itself moving relative to the CMB at regarding 370 kilometers per second.
This motion will give rise to a dipole signal in light from any astrophysical source, but so far the CMB is the only one that has been accurately measured. By looking for the pattern in other forms of light, astronomers might confirm or challenge the idea that the dipole is due entirely to the motion of the solar system.
“This measurement is important because disagreement with the size and direction of the CMB dipole might provide us with insight into the physical processes that were operating in the early universe, potentially even when it was less than a trillionth of a second old,” he said in a statement. co-author Fernando Atrio-Barandela, professor of theoretical physics at the University of Salamanca.
Scientists manage to capture a gamma ray signal | Photo: European Space Agency
The team reasoned that by adding many years of data from Fermi’s LAT (Large Area Telescope), which scans the entire sky many times a day, a related dipole emission pattern might be detected in gamma rays. Thanks to the effects of relativity, the gamma-ray dipole should be amplified up to five times more than the CMBs currently detected.
The scientists combined 13 years of Fermi LAT observations of gamma rays above regarding 3 billion electron volts (GeV); For comparison, visible light has energies between 2 and 3 electron volts. They removed all resolved and identified sources and removed the central plane of our Milky Way to analyze the extragalactic gamma-ray background.
“We found a gamma-ray dipole, but its peak is in the southern sky, far from the CMB, and its magnitude is 10 times larger than we would expect from our motion,” said co-author Chris Shrader, an astrophysicist at Catholic University. of America in Washington and in Goddard. “While it is not what we were looking for, we suspect it may be related to a similar feature reported for higher energy cosmic rays.”
Cosmic rays are accelerated charged particles, mainly protons and atomic nuclei. The rarest and most energetic particles, called UHECR (ultra-high energy cosmic rays), carry more than a billion times the energy of 3 GeV gamma rays, and their origins remain one of the biggest mysteries in astrophysics.
Since 2017, the Pierre Auger Observatory in Argentina has reported a dipole in the arrival direction of UHECRs. Being electrically charged, cosmic rays are deflected by the galaxy’s magnetic field by different amounts depending on their energies, but the UHECR dipole peaks at a location in the sky similar to what Kashlinsky’s team finds in the rays. gamma. And both have strikingly similar magnitudes: regarding 7% more gamma rays or particles than average coming from one direction and correspondingly smaller amounts arriving from the opposite direction.
Cosmic ray Amaterasu | Photo: Osaka Metropolitan UniversityL-INSIGHT, Kyoto UniversityRyuunosuke Takeshige
Scientists believe that the two phenomena are likely related: that as yet unidentified sources are producing both gamma rays and ultra-high-energy particles. To solve this cosmic enigma, astronomers must locate these mysterious sources or propose alternative explanations for both features.
*With information from Europa Press.
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