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Gamma-Ray Burst Strikes Earth From Distant Exploding Star

A gamma-ray burst from a galaxy 2 billion light-years away impacts Earth's ionosphere
A gamma-ray burst from a galaxy 2 billion light-years away impacts Earth’s ionosphere. Credit: ESA

INTEGRAL, short for International Gamma-Ray Astrophysics Laboratory, was sent into space by ESA in 2002. Since then, it has been finding gamma-ray bursts almost every day. This time, however, it was different, and GRB 221009A stood out.

An especially bright and long-lasting burst of gamma rays, called GRB 221009A, caught the attention of high-tech satellites circling the Earth. Like ESA’s INTEGRAL mission, these satellites are always on the lookout for such cosmic events.

Mirko Piersanti, from the University of L’Aquila in Italy and the leader of the team sharing these findings, said, “It was probably the brightest gamma-ray burst we have ever detected.”

Gamma ray bursts lead to powerful energy releases

Once a mystery, gamma-ray bursts are now known to be powerful energy releases from exploding stars such as supernovas or the collision of two incredibly dense neutron stars.

Pietro Ubertini, co-author and principal investigator for INTEGRAL’s IBIS instrument, based in Rome, Italy, states, “We’ve been measuring gamma-ray bursts since the 1960s, and this is the strongest ever measured.”

Its strength is so remarkable that the closest comparison on record is ten times less powerful. In terms of statistics, a gamma-ray burst as potent as GRB 221009A hits Earth only once every ten thousand years.

For about eight hundred seconds, when the gamma rays hit, the energy was strong enough to trigger lightning detectors in India. Instruments in Germany picked up on the fact that the blast disturbed Earth’s ionosphere for several hours. This huge burst of energy got scientists thinking about how our planet’s ionosphere is affected in such instances.

Detection of gamma ray burst ionosphere effects by CSES

One of the spacecraft keeping an eye on the ionosphere is the China Seismo-Electromagnetic Satellite (CSES), also called Zhangheng. Launched in 2018 as a collaboration between China and Italy, it assesses the upper part of the ionosphere for any changes in electromagnetic behavior.

While its main job is to study if there is a connection between ionosphere changes and seismic events such as earthquakes, it can also help in evaluating how solar activity affects the ionosphere.

Mirko and Pietro, both part of the CSES science team, thought that if the gamma-ray burst had caused a disturbance, CSES would have detected it. However, they couldn’t be certain. Pietro explains, “We had looked for this effect from other GRBs in the past but had seen nothing.”

Gamma rays impacting the bottom side of the ionosphere

In the past, researchers noticed gamma-ray bursts (GRBs) impacting the bottom-side ionosphere at night when the sun’s influence is minimal. However, they never observed such effects on the top side.

This led to the belief that, by the time a GRB reached Earth, its power was too weak to cause changes in ionospheric conductivity, resulting in an electric field shift.

This time, luck was on the scientists’ side. When they investigated, they found something new. For the first time, they witnessed a significant disturbance—an intense electric field shift—on the top side of the ionosphere.

Erik Kuulkers, ESA Project Scientist, expresses amazement, “It is amazing. We can see things that are happening in deep space but are also affecting Earth.”

Laura Hayes, a research fellow and solar physicist at ESA, remarks, “Notably, this disturbance impacted the very lowest layers of Earth’s ionosphere, situated just tens of [kilometers] above our planet’s surface, leaving an imprint comparable to that of a major solar flare.”

This mark appeared as an increase in ionization in the bottom-side ionosphere. It was detected through very low-frequency radio signals bouncing between the ground and Earth’s lower ionosphere.

Laura clarifies, “Essentially, we can say that the ionosphere ‘moved’ down to lower altitudes, and we detected this in how the radio waves bounce along the ionosphere.” She shared these findings in 2022.

Potential consequences of supernova

The recent discovery validates the concern about the potential consequences of a supernova in our own galaxy. Mirko emphasizes, “There has been a great debate about the possible consequences of a gamma-ray burst in our own galaxy.”

In the worst scenario, such a burst wouldn’t just impact the ionosphere. It could harm the ozone layer. This could allow harmful ultraviolet radiation from the Sun to reach the Earth’s surface.

Scientists speculate that this effect might have played at least somewhat of a role in mass extinction during Earth’s history. However, we need much more data to conclusively determine this.

Now armed with a clearer understanding of what to look for, the research team has begun analyzing data from CSES and matching it with other gamma-ray bursts observed by INTEGRAL.

While the available data goes back only to 2018, which is when CSES was launched, a follow-up mission is already in the works. This ensures that exciting new insight into how Earth interacts with the distant universe will continue to be explored.

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