Using modern particle physics, researchers have discovered a massive void within the Great Pyramid of Khufu on the outskirts of Cairo, which could help unlock the mystery of how the ancient structure was constructed.

The international team scanned the pyramid with muons, subatomic particles that can pass through bedrock even 1 kilometer thick.

Japanese researchers from Nagoya University and the High Energy Accelerator Research Organization participated in the project. The team's findings were posted on Nov. 2 on the British science journal Nature website.

"The creation of a void might have been a structural method used to reduce the pressure from the stones," said Michinori Ohshiro, a professor of Egyptology at Komazawa University in Tokyo. "The research results could lead to an understanding of the construction methods used for the pyramid."

While researchers have studied the interior of the Great Pyramid since the Middle Ages, its construction is still one of the many mysteries remaining about one of the Seven Wonders of the Ancient World.

Scientists believe the pyramid, which stands 139 meters tall and has a square base with each side measuring 230 meters, was constructed around 2,500 B.C.

Kunihiro Morishima, an assistant professor of physics at Nagoya University, and others focused on the imaging technique called muography to survey the internal construction of the pyramid.

A special film was placed within what is called the queen's chamber of the pyramid to detect the muons. The study has been continuing since 2015 and the accumulated data was analyzed. That led to the discovery of the huge void above the queen's chamber.

The huge chamber is located near the center of the pyramid interior and is about 50 to 70 meters above the ground. It is believed to be about 30 meters long. While the surface area is still unclear, researchers believe it is of the same scale as the large gallery within the pyramid that measures one to two meters wide and nine meters high.

(This article was written by Ryoma Komiyama and Nobutaro Kaji.)