On October 9, 2022, at 3:21 p.m. (Spanish peninsular time), several observation satellites in Earth orbit, both from NASA and the European Space Agency (ESA), detected a powerful emission of high-energy radiation , in the form of gamma rays, coming from a galaxy located 2,000 million light-years away and probably caused by the death of a massive star.
This emission was the most intense ever received and the event that generated it released, in just 800 seconds, hundreds of times the energy that the Sun will emit in its entire life (10 billion years). Now a recently published study shows that its arrival caused disturbances in the upper layer of the Earth's ionosphere, a fact unprecedented until now, and points to the possibility that a similar event, but much closer, could have consequences for life on Earth. .
The so-called explosions (also bursts or outbreaks) of gamma rays are sudden phenomena, of very short duration (typically on the order of seconds to a few minutes) in which an enormous amount of high-energy light is emitted into space in the form of gamma rays. . As fortunately for life on Earth, this radiation is filtered by the atmosphere, the main gamma ray detectors are located in Earth orbit.
The outbreak detected in October 2022 received the scientific name GRB 221009A, but is informally known as BOAT (the acronym in English that means the greatest of all time). In fact, it exceeds at least 10 times the power of the most intense one known up to that point and was so powerful that it even saturated the detection capacity of most instruments designed specifically for the study of this type of phenomena. The arrival of the radiation occurred over India and illuminated large areas of Europe, Africa, Asia and part of Australia.
Initially, it was thought that its origin was in our galaxy, but observations made with various satellites and also with the VLT telescope of the European Southern Observatory confirmed that the source was in a very distant galaxy, 2 billion light years away. . Subsequently, observations made with the Gran Telescopio de Canarias confirmed the presence, in this galaxy, of a luminous remnant compatible with the explosion of a very massive star.
The event that generated the gamma ray outbreak had to release a huge amount of energy. According to the European Space Agency (ESA), the arrival to Earth of radiation from such an extreme phenomenon could occur statistically every 10,000 years, so, as stated by Alicia Rouco Escorial, specialist in gamma ray outbreaks at ESA , “we have been very fortunate to be able to capture it.”
In the 800 seconds that it lasted, the radiation beam that reached our planet caused various effects, including the activation of lightning detectors in India and, much more relevant, disturbances in the Earth's ionosphere, a region of the Earth's atmosphere that is It is between 50 and 950 kilometers high.
The Earth's ionosphere is mainly composed of electrically charged particles, such as electrons and ions, that are generated due to the incidence of solar radiation on air molecules. It is an atmospheric layer essential for the propagation of radio waves.
Until now, the gamma ray bursts detected, despite being enormously energetic in origin, had arrived at Earth sufficiently weakened due to the distance traveled. Only a few had managed to affect the ionosphere, and even then only partially. Specifically, the few disturbances observed had occurred in the lower layer of this region of the atmosphere and were only detectable at night, when the dominant influence of solar radiation had disappeared.
But in the recently published study, the researchers present the detection of strong disturbances, due to the BOAT outbreak, also in the highest layer of the ionosphere. In fact, the effects were so clear that they could even be captured by instruments whose function is to analyze the effects caused by powerful solar flares, and all this despite the very distant origin of the gamma ray outbreak.
The disturbances affected the bouncing of very low-frequency radio waves between the Earth's surface and the bottom of the ionosphere. Scientific analysis revealed an increase in the amount of ionized (electrically charged) particles in this region of the atmosphere. As Laura Hayes, an ESA researcher specializing in solar physics, comments, “essentially we can say that the ionosphere moved downward.”
The enigma about the cause of gamma ray bursts began with the first detections, in the 1960s. For years, there was doubt about the origin of these phenomena, capable of releasing, in moments, the energy generated by the Sun throughout its life (10 billion years).
In 1997, the Italian-Dutch BeppoSAX satellite was able to obtain such precise and rapid location measurements of one of these gamma ray bursts that other instruments, including optical telescopes, were able to confirm that the source was very distant and outside our orbit. galaxy. Currently, according to ESA, on average, one burst of gamma rays is received per day.
Not all outbreaks are the same, and in general they can be grouped based on their duration, which suggests that the cause that generates them is different. Thus, it is thought that flares of longer duration (a few minutes) are caused by the explosion of very massive stars, an event called hypernova. On the contrary, bursts of shorter duration (a few seconds at most) could be emitted at the final moment of the merger of two neutron stars or two black holes.
Gamma ray bursts can have devastating effects on life. The ESA estimates that the radiation alone could sterilize a planet at a distance of 200 light years. But even if the radiation source were much further away, the abrupt increase in atmospheric ionization caused by an extremely intense outbreak would destroy the ozone layer, the natural protection that prevents ultraviolet radiation from the Sun. , very harmful to life, reaches the surface of the planet.
Although gamma ray bursts are very directional and the probability of being in their path is very low, there is evidence to suggest that these phenomena could have caused some of the great extinctions of life on Earth. However, the European space agency points out, much more data will be needed to confirm this assumption.
