by Astronomers have discovered an unexpected and unexplained feature outside our Milky Way galaxy that radiates 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 serendipitous discovery,” Kashlinsky said in a statement. “We found a much stronger signal and in a different part of the sky than what we were looking for.”
What makes this gamma-ray signal even stranger is the fact that it is located towards another unexplained feature in space, the source of some of the most energetic cosmic particles ever detected.
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The team believes the new signal is related to these high-energy particles, or cosmic rays, which are composed mainly of protons, neutrons and atomic nuclei.
These ultra-high-energy cosmic rays (UHECR) carry more than a billion times the energy of gamma rays, and their origins remain one of the biggest mysteries in astrophysics, a mystery that the discovery of this gamma-ray source go deeper.
Search for cosmic fossils led to gamma ray surprise
This mysterious new feature of gamma rays may be similar to a peculiar feature of the cosmic microwave background (CMB).
The CMB represents the oldest light in the universe and is a cosmic fossil left over from an event that occurred about 380,000 years after the Big Bang. Before this, the universe had been a hot, dense soup of free electrons and protons through which light could not travel.
However, around this time the universe cooled enough to allow electrons and protons to join together to form primordial atoms. The sudden lack of free electrons meant that photons, particles of light, were no longer scattered infinitely by these negatively charged particles.
The universe effectively went from opaque to transparent in an instant, allowing the first light to travel. The CMB is made up of these first free-traveling photons.
Related: What is the cosmic microwave background?
As the universe expanded over the next nearly 13.8 billion years, these photons lost energy and now have a uniform temperature of a chilling -454 degrees Fahrenheit (-270 degrees Celsius).
The CMB was first detected by American radio astronomers Robert Wilson and Arno Penzias in May 1964 as microwave radiation in all directions of the sky above Earth. In the 1990s, however, this apparent uniformity was questioned when NASA’s Cosmic Background Explorer (COBE) spacecraft discovered small variations in the CMB temperature.
COBE found that the CMB is 0.12% hotter and has more microwaves toward the direction of the Leo constellation and is 0.12% cooler than average in the opposite direction, with fewer microwaves.
This pattern, or “dipole,” in the CMB has been attributed to the motion of our solar system: 230 miles per second relative to the fossil radiation field. However, if this were the case, similar dipoles caused by the motion of the solar system should arise with all the light coming from astrophysical sources far beyond the solar system, something that has not been observed so far.
Astronomers are looking for this effect in other types of light in order to confirm that the CMB dipole is the result of our motion.
“This measurement is important, because a disagreement with the size and direction of the CMB dipole could give us 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,” the member said. of the team Fernando Atrio-Barandela, professor of theoretical physics at the University of Salamanca in Spain.
A cosmic mystery or two?
The team turned to Fermi and its Large Area Telescope (LAT), which scans Earth’s entire sky several times a day to collect and collate many years of data. The researchers hoped that buried within the LAT data was a dipole emission pattern that could be detected in gamma rays.
Due to the effects of special relativity and the high-energy nature of gamma rays, such a dipole should be five times more prominent in these data than in the low-energy microwave light from the CMB. The team found something similar to this pattern, but not where they expected.
“We found a gamma-ray dipole, but its peak is in the southern sky, far from the CMB [peak]and its magnitude is 10 times greater than we would expect from our motion,” said team member Chris Shrader, an astrophysicist at the Catholic University of America. “Although it’s not what we were looking for, we suspect it may be related to a similar feature. reported for the highest energy cosmic rays”.
There is a corresponding dipole in the showers of high-energy charged particles that make up UHECRs as they reach Earth, which was first detected by the Pierre Auger Observatory in Argentina in 2017.
Although these charged particles deflect from the Milky Way’s magnetic field and other magnetic fields as they travel toward Earth, and the strength of this deflection depends on the energy of the particle and its charge, the UHECR dipole still reaches its point. maximum in one place. similar to where Kashlinsky and his colleagues found the gamma ray source.
The team theorizes that, because of this correlation in location, the mysterious gamma rays and UHECRs are likely related, especially considering that unidentified sources are producing both phenomena.
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Astronomers now want to investigate the locations of these emissions to determine the source, or perhaps sources, of this ultra-high-energy light and these ultra-high-energy particles to see if they are really connected and if they represent a cosmic mystery to solve or two.
The team’s findings were presented at the 243rd meeting of the American Astronomical Society in New Orleans, Louisiana, by Kashlinsky and are discussed in a paper published Wednesday (Jan. 10) in The Astrophysical Journal Letters.
