Astronomers have discovered an unexpected and unexplained feature outside our Milky Way galaxy that emits high-energy light called gamma rays.
The team behind the discovery, including NASA and University of Maryland cosmologist Alexander Kashlinsky, found the gamma ray signal while searching through 13 years of data from NASA’s Fermi Telescope.
“This is a completely accidental discovery,” Kashlinsky said in a statement. “We found a much stronger signal than we were looking for, and it’s in a different part of the sky.”
What makes this gamma-ray signal even stranger is that it is positioned towards another unexplained feature in space, the source of some of the most energetic cosmic particles ever detected.
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The team thinks that the newly discovered signal is related to these high-energy particles, or cosmic rays, which are mostly composed of protons, neutrons and atomic nuclei.
These ultra-high-energy cosmic rays (UHECRs) carry more than a billion times the energy of gamma rays, and their origin remains one of the greatest mysteries in astrophysics; a mystery deepened by the discovery of this gamma-ray source.
Cosmic fossil hunt leads to gamma ray surprise
This new mysterious gamma ray feature may resemble a peculiar characteristic of the cosmic microwave background (CMB).
CMB represents the oldest light in the universe and is a cosmic fossil left over from an event that occurred approximately 380,000 years after the Big Bang. Before this, the universe was a hot, dense soup of free electrons and protons that light could not pass through.
But around this time, the universe had cooled enough to allow electrons and protons to come together to form primitive atoms. The sudden absence of free electrons meant that photons, particles of light, were no longer scattered indefinitely by these negatively charged particles.
The universe suddenly went from opaque to transparent, allowing the first light to travel. The CMB consists of these first free-floating photons.
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As the universe expanded over the next almost 13.8 billion years, these photons lost energy and now have a uniform temperature of a freezing temperature of minus 454 degrees Fahrenheit (minus 270 degrees Celsius).
CMB was first detected in May 1964 by American radio astronomers Robert Wilson and Arno Penzias as microwave radiation in all directions of the sky on Earth. But in the 1990s, this apparent uniformity was challenged when NASA’s Cosmic Background Explorer (COBE) spacecraft discovered small variations in CMB temperature.
COBE found that the CMB is 0.12% warmer and has more microwaves in the direction of the constellation Leo, while in the opposite direction it is 0.12% cooler and has fewer microwaves than average.
This pattern or “dipole” in the CMB is attributed to the motion of our solar system relative to the fossil radiation field, which is 230 miles per second. But if this were the case, similar dipoles caused by the motion of the solar system should appear in all light from astrophysical sources far beyond the solar system, but this has not been seen to date.
Astronomers are also looking for this effect in other types of light, so they can confirm that the CMB dipole is the result of our motion.
“Such a measurement is important because a disagreement about the size and orientation of the CMB dipole could give us a glimpse into the physical processes operating in the very early universe, potentially down to times of less than a trillionth of a second,” he said of the theory at the University of Salamanca in Spain. team member Fernando Atrio-Barandela, professor of physics.
One cosmic mystery or two?
The team turned to Fermi and its Large Area Telescope (LAT), which scans the entire sky on Earth several times a day, to collect and collate many years of data. The researchers hoped that a dipole emission pattern that could be detected in gamma rays was embedded within the LAT data.
Due to the effects of special relativity and the high-energy nature of gamma rays, such a dipole should be five times more apparent in these data than in the low-energy microwave light of the CMB. The team found something resembling this pattern, but not where they expected.
“We found a gamma-ray dipole, but its peak is located in the southern sky, away from that of the CMB.” [peak]”Although it wasn’t what we were looking for, we suspect it might be related to it,” said team member Chris Shrader, an astrophysicist at the Catholic University of America. “It resembles a similar feature reported for the highest energy cosmic rays.”
High-energy charged particles, including UHECRs, have a corresponding dipole in their showers when they arrive on Earth, which was first detected by the Pierre Auger Observatory in Argentina in 2017.
Even though these charged particles receive deflections from the Milky Way’s magnetic field and other magnetic fields as they travel towards Earth, and the strength of this deflection depends on the energy and charge of the particle, the UHECR dipole still peaks at a location where It’s similar to where Kashlinsky and his colleagues found the gamma ray source.
Because of this correlation in location, the team theorizes that the mysterious gamma rays and UHECRs are likely linked, especially considering that unidentified sources produce both phenomena.
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Astronomers now want to investigate the source of this ultra-high-energy light and these ultra-high-energy particles, or perhaps the locations of these emissions, to determine their source, and to see whether they are truly connected and whether they represent a cosmic mystery that needs to be solved. two.
The team’s findings were presented by Kashlinsky at the 243rd meeting of the American Astronomical Society in New Orleans, Louisiana, and discussed in a paper published Wednesday, January 10, in The Astrophysical Journal Letters.