[Reading Science] "How Big a Star Died?"... The Strongest Explosion Ever Recorded

NASA Research Team Announces Analysis of 'Strongest Ever' Gamma-Ray Burst Phenomenon from Last October
"Once in 10,000 Years Probability"... Analyzed as Explosion of Supergiant Star

In early October last year, an ultra-powerful gamma-ray burst phenomenon struck within the solar system, shocking astronomers. Analysis revealed that it was the most powerful event ever recorded in human history, occurring roughly once every 10,000 years.

The National Aeronautics and Space Administration (NASA) announced on the 29th that a research team led by Eric Burns, a professor at Louisiana State University, presented a paper on this phenomenon at the 20th High Energy Astrophysics Division meeting of the American Astronomical Society held in Hawaii on the 28th (local time).

On October 9th last year, gamma-ray observation instruments installed on multiple space telescopes, including the Hubble, detected a gamma-ray burst (GRB) phenomenon of unprecedented strength, named GRB 221009A. Astronomers also gave it the nickname "BOAT," meaning "brightest of all time."

The most powerful gamma-ray burst ever recorded captured by the Hubble Space Telescope (red circle). Photo by NASA

Professor Burns' research team has been studying how frequently such a gamma-ray burst of this magnitude could occur, using data observed by NASA's Fermi Gamma-ray Space Telescope, Russia's Konus instrument, and NASA's Wind satellite.

At the meeting, Professor Burns explained, "(GRB 221009A) was definitely a monstrous explosion and very special; nothing of similar scale has ever been observed before. It is an event that could occur once every 10,000 years. It may be the brightest gamma-ray burst to have struck Earth since the dawn of human civilization."

In fact, the gamma-ray burst was so intense that it temporarily disabled gamma-ray observation equipment installed on most satellites and space telescopes, making real-time intensity measurement impossible. The explosion, spanning a broad spectrum from radio waves to gamma rays, was detected by NASA and other countries' observation instruments. The International Space Station's (ISS) X-ray telescope, NASA's neutron detection equipment, and even Voyager 1, traveling through interstellar space, sent back detection results.

The research team recovered data from the Fermi Gamma-ray Space Telescope and compared it with data from Russia, China, and NASA's historical GRB measurements. The results concluded that it was more than 70 times stronger than any previously observed explosion. It occurred about 1.9 billion light-years away and involved a very powerful explosion lasting more than 2 seconds, making it one of the longest-lasting GRBs discovered to date. It released more energy in a few seconds than the Sun produces over approximately 10 billion years.

NASA stated, "Astronomers believe this explosion was caused by the core of a massive star collapsing and exploding due to its own mass, resulting in the birth of a new black hole. As the black hole rapidly absorbed surrounding material, it emitted jets containing particles accelerated close to the speed of light in opposite directions, which produced powerful X-rays and gamma rays that were ejected into space."

So far, astronomers understand that gamma-ray bursts occur due to two causes. If the burst lasts less than 2 seconds, it is caused by the collision of ultra-dense stars like neutron stars. If it lasts longer, up to several minutes, it occurs when a massive star collapses and dies, giving birth to a black hole. This event lasted more than 2 seconds and is presumed to be related to black hole formation.

When this type of GRB occurs, a bright supernova (a phenomenon where a star explodes and transitions into a black hole, shining very large and bright) typically appears within a few weeks. However, none has been discovered yet, leaving it a mystery. Scientists believe that even if a supernova occurred at the location, observation might be difficult. GRB 221009A appeared just a few degrees above the plane of our Milky Way galaxy, meaning most of its light could be blocked by thick dust.

Andrew Levan, an astronomy professor at Radboud University in the Netherlands and a member of the research team, said, "Although the explosion was incredibly bright, we cannot conclude that a supernova occurred. We need to keep observing, but it is possible that the entire star transitioned directly into a black hole without exploding. We plan to conduct additional observations within weeks using the James Webb Space Telescope (JWST) and Hubble."