Recently discovered light from the Sun has been found to be the most energetic light ever seen, posing a new challenge for solar physicists to tackle.
The first known discovery of solar gamma radiation in the teraelectronvolt (TeV) range has been made as a consequence of a 6-year observing program involving more than 30 institutions from North America, Europe, and Asia.
Contrary to what you might anticipate, however, it did not coincide with increased solar activity—or even any solar activity. Instead, the Sun was very quiet at the time of the detection, which leaves our current theories of the Sun unable to fully explain it.
The Sun is the star in the universe that has been researched the most. From low-frequency radio waves to gamma radiation, the most energetic light in the universe, we have data across the entire spectrum. Despite this, there are still many things about our hometown celebrity that we don’t know. We still don’t know the specifics of its operations.
Although we are aware that magnetic fields are significant and play a significant part in almost all of the solar activity we observe, the underlying mechanisms are not well understood. We try to learn more by observing the light that the Sun emits.
One of the resources we employ for researching the cosmic and gamma radiation from space that interacts with Earth’s atmosphere is the High Altitude Water Cherenkov (HAWC) observatory in Mexico.
Although the atmosphere prevents this radiation from reaching us, it can nevertheless result in high-energy particles that can be seen in the dark and whose source gamma ray energy and direction can be determined from that observation.
According to the multinational HAWC Collaboration, which carried out the study, “HAWC is among the few detectors capable of observing the Sun in the TeV range.” Because of its wide field of vision and high livetime fraction, it is possible to continuously expose the image as the Sun crosses the sky.
The researchers identified emissions ranging from 0.5 to 2.6 TeV (one TeV is a trillion electronvolts) emanating from the direction of the Sun in data gathered using HAWC between 2014 and 2021. With a 6.3 sigma probability, their new analysis pipeline determined that this emission was coming from the Sun.
Not the most energetic light ever observed in space. The sighting of 450 TeV gamma rays emanating from the Crab Nebula few years ago set the record for this. But for our own star, it’s a brand-new hit.
According to Michigan State University astroparticle physicist Mehr Un Nisa, “out popped this excess of gamma rays after looking at six years’ worth of data.”
We immediately thought, “We definitely messed this up,” upon seeing it. At these energies, the sun cannot be as brilliant.
We are aware that the Sun occasionally behaves badly. It reacts by ejecting coronal mass ejections and solar flares. The Sun does not only provide light, though. It also strikes it. The larger galaxy’s cosmic rays are constantly pouring through space. These cosmic rays interact with the atmosphere here on Earth to create a gamma ray glow.
On the Sun, a process akin to this is thought to occur. The solar atmosphere experiences collisions with galactic cosmic rays in the gigaelectronvolt (1 billion electronvolt) range.
The team believes that this interaction is most likely what caused the TeV emission. Additionally, they examined the GeV data gathered by HAWC and NASA’s Fermi LAT gamma-ray satellite observatory and discovered that the GeV emission was brighter and more abundant than anticipated during the Sun’s quiet phases.
We don’t know how the discharge becomes that brilliant, though. It is incompatible with theoretical models. Given how terrible the Sun’s magnetic fields are, it is likely that they are involved. In fact, a report released earlier this year put out the idea that the solar magnetic fields serve as cosmic ray electron accelerators to create synchrotron gamma radiation.
It will take further modeling to ascertain the precise mechanism behind this, though.
The HAWC Collaboration claims that “models of cosmic ray interactions in the Sun… already under-predict the observed gamma-ray flux from the Sun in the GeV range.” “Our observations highlight the need for a revised framework that can explain the anomalous excess of gamma rays from the Sun, also in the TeV range.”
It will take further modeling to ascertain the precise mechanism behind this, though.
The research has been published in Physical Review Letters.