A gamma-ray burst could alter the Earth's ionosphere

Scientists have proven that one of the brightest gamma-ray flashes in the history of observations, which occurred in October 2022, affected both the lower and upper parts of the Earth's ionosphere - the shell that protects us from cosmic radiation.

The ionosphere is the upper part of the Earth's atmosphere ionized by solar and cosmic radiation. It begins at a height of about 60 kilometers and plays a major role in protecting the planet's surface from dangerous radiation, including gamma flashes coming from deep space.

Gamma-ray flares are some of the most energetic events in the Universe. They can be both short and long-lasting, occurring when massive stars die and neutron stars merge.

One such extremely bright and prolonged gamma-ray burst - GRB221009A - "reached" Earth on October 9, 2022. It lasted hundreds of seconds and was recognized as one of the brightest gamma-ray bursts for half a century of observations. Astronomers immediately noticed a disturbance in the lower layers of the ionosphere, triggered by the burst, at altitudes from 60 to 350 kilometers.

In a new paper published in the journal Nature Communications, scientists have provided evidence of a strong perturbation and in the upper layers of the ionosphere - at a height of 507 kilometers. The disturbance caught the detector of electric fields, installed on the Chinese seismo-electromagnetic satellite (CSES), which at the time of the outbreak flew in low-Earth orbit from north to south over the territory of Europe.

Obtained from the satellite danami indicate anomalous ionization of the ionosphere. Usually such disturbances - the result of solar flares and other events associated with the activity of the luminary. The authors of the new study hypothesized that such a powerful perturbation of the electric field of the ionosphere at an altitude of 507 kilometers provoked only a change in plasma density due to the ionizing effect of gamma-ray burst.

To test this version, the researchers studied the distribution of electron density in the ionosphere over Europe according to GNSS satellites and built an analytical model of the effect of gamma-ray bursts on the electric fields of the upper layers of the ionosphere.

It turned out that gamma-ray bursts do not have a significant effect until the crossing of a certain threshold in the ratio of the rate of appearance of new ions under the influence of the flash to the natural rate of absorption of these ions in the ionosphere. This confirms the earlier hypothesis that the interaction between gamma-ray flares and the upper atmosphere is a threshold process.

Over the past ten years, specialized satellites "catch" an average of one gamma-ray burst per day, but very rarely due to such bursts there are disturbances in the ionosphere - and not once these disturbances have not noticed in the upper layers of the ionosphere.

The unusual nature of the new discovery is that until now it was thought that only events on the Sun could perturb the ionosphere so strongly. That gamma-ray flashes, whose sources may lie millions of light years away from us, can seriously affect the Earth, quite unexpected. Since the strength of gamma-ray flares often varies considerably, it is possible that the strongest of them could have an even more serious effect on the Earth's atmosphere.