Earlier this year, there were reports that the Earth was hit by the brightest gamma-ray burst since the birth of human civilization. Now, a team of astronomers has assigned a value to the energy contained in these gamma-ray bursts, and it's staggering, to say the least.
Gamma-ray bursts are the brightest explosions seen on Earth, and there are many theories about their origin. Some believe they are caused by collisions of neutron stars; others believe they are caused by the merger of a neutron star and a black hole or the collapse of a massive star into a black hole. Theories about their brightness focus on their afterglow radiation. The collision of fast-moving materials produces shock waves that accelerate electrons, which further collide and produce high-energy gamma rays. The result is the brightest explosion ever detected.
The gamma-ray burst (GRB) reported in April this year has actually been confirmed by NASA to have hit the Earth on October 9, 2022, and originated approximately 2.4 billion light-years away. NASA called this a "once-in-10,000-year" event and said it was likely caused by a black hole created when a supermassive star collapsed inward. The shock wave generated by such a huge galactic event released gamma rays.
Technically, the burst is called GRB221009A, but its more friendly name is Brightest Ever, or BOAT.
Now, researchers at China's Large Upper Air Current Survey Observatory (LHAASO) have calculated the energy contained in these gamma rays: 13 teraelectronvolts (TeV). They also say that the object whose collapse released all this energy was a star, about 20 times larger than our sun.
The final number fell short of the 18 teraelectronvolts predicted when the explosion was first observed, but it was still a huge amount of energy. Electron volts are a special measurement of the kinetic energy gained by electrons under certain constraints when they are accelerated in a vacuum. One teraelectronvolt is equal to 1,012 electron volts. The acceleration of most GRBs is in the 0.5TeV range. BOAT's 13 teraelectronvolts is even more amazing. It holds the record for the largest energy GRB ever witnessed on Earth, and is also the first time a GRB exceeding 10 teraelectronvolts has been detected.
Second in the race for cosmic GRBs is one likely caused by neutron star collisions, which was reported less than a month ago.
The research team said that LHAASO's ability to measure such huge GRB energy may indicate that the Milky Way space may be more transparent than previously thought. The team plans to continue studying BOAT, specifically why the event's afterglow lasted so much longer than our current understanding of GRBs suggests.
The researchers describe their measurement process in a paper published in the journal Science Advances and give special thanks to the team involved in the work.
"We would like to thank all the staff who work year-round at the LHAASO site at an altitude of 4,400 meters, maintaining the detectors and keeping the water circulation system, power supply and other components of the experiment running smoothly," they wrote.