While the Milky Way’s supermassive black hole may appear relatively calm, the galaxy’s core is far from tranquil. The central region of our galaxy, home to the enigmatic black hole Sagittarius A*, has revealed the presence of a powerful cosmic accelerator known as a PeVatron. This discovery marks a significant addition to the galactic center’s list of extreme phenomena.
A team of researchers, using the High-Altitude Water Cherenkov (HAWC) observatory located in Mexico’s mountains, has detected repeated emissions of high-energy gamma rays from a mysterious source near the galactic center. Over a span of seven years, the observatory recorded 98 gamma-ray events exceeding 100 teraelectronvolts (TeV) from a source named HAWC J1746-2856.
“This is a glimpse at the center of the Milky Way at energy levels higher than ever seen before,” says Pat Harding, a physicist at Los Alamos National Laboratory. “The research confirms a PeVatron source of ultrahigh-energy gamma rays at the Galactic Center Ridge, demonstrating that the center of our galaxy hosts some of the Universe’s most extreme physical processes.”
What is a PeVatron?
A PeVatron is a natural particle accelerator capable of accelerating cosmic rays charged protons and atomic nuclei traveling nearly at the speed of light up to extremely high energies. These powerful environments can include supernova remnants, star-forming regions, and the intense magnetic fields around supermassive black holes. If these cosmic rays decelerate suddenly due to an interaction with dust clouds or magnetic fields, they release energy in the form of gamma radiation.
Despite their power, finding PeVatrons is a rare occurrence, particularly within our galaxy. The intense gamma radiation they produce is difficult to detect directly from the ground due to Earth’s atmosphere. However, when gamma rays enter the atmosphere, they generate showers of lower-energy particles, which can be captured using Cherenkov detectors like HAWC.
HAWC’s Discovery of HAWC J1746-2856
HAWC is highly sensitive to TeV gamma-ray energies and has been instrumental in several key discoveries. This new research, led by physicist Sohyoun Yu Cárcaron of the University of Maryland, examined 2,546 days of data from the HAWC observatory. Among the data, the team detected 98 powerful gamma-ray emissions originating from a single point source in the galactic center, now designated HAWC J1746-2856.
The source of these gamma rays remains a mystery, as no known supernova remnants coincide with its location. There are two nearby candidates: the supermassive black hole Sagittarius A* and a known gamma-ray emitter named HESS J1746-285, located near a galactic feature known as the Radio Arc.
Although the exact nature of HAWC J1746-2856 remains uncertain, the discovery confirms the existence of a PeVatron at the galactic center, shedding light on the extreme physical processes at work in the Milky Way’s core.
What’s Next?
The study also suggests a higher density of cosmic rays in the galactic center, hinting at a fresh source of accelerated protons. However, resolving the mystery of HAWC J1746-2856 may require more advanced observations from the next generation of Cherenkov detectors.
For now, the galactic center continues to surprise scientists, reinforcing the idea that the heart of our galaxy is home to some of the most powerful and enigmatic forces in the universe.
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