It could be the ultimate archaeological discovery: a previously unknown chamber lurking beneath the stones of the Great Pyramid at Giza in Egypt. Now, a team using a cutting edge imaging technique called muography has picked up signals indicating a hidden corridor behind the famous chevron blocks on the pyramid's north face.

Muography can detect voids or empty spaces inside thick layers of earth or stone, and it is often used to plumb the depths of volcanoes. Muons are cosmic particles that hit the Earth at an average rate of 10,000 per m² per minute, though they can be absorbed or deflected by dense material. To find voids in rock, researchers set up muon-detecting plates inside a corridor in the pyramid, and they measured the amount of muons that hit over a period of 67 days. By analyzing absorption patterns in the muons that hit the plates, the researchers were able to create a 3D model showing where empty spaces might be in the structure.

What they found was an ambiguous void behind a stone chevron structure on the north face of the pyramid. This chevron is not a decoration—indeed, it would have been hidden behind the outer surface of the pyramid when it was completed 4,500 years ago. Instead, chevrons are often used to maintain structural integrity in areas with ceilings. It appears likely that additional chevron structures below the remaining one have fallen off the pyramid over time. The fact that these chevrons appear over the putative empty space offers further evidence that the team may have found a hidden chamber.

That said, many researchers are cautioning that we need to gather more evidence before we make plans to open the pyramid. For now, this is merely an anomaly, not a verified hidden chamber. Former Egyptian antiquities minister Zahi Hawass told Live Science that "the core [of the pyramid] has big and small stones, and this can show hollows everywhere." He and his team have asked for another year of funding for the imaging group, called the Scan Pyramids Mission, to gather more data.

Scan Pyramids Mission previously used thermal imaging to look for anomalies in the Great Pyramid that might reveal the locations of hidden chambers. When the pyramid is heating up in the morning or cooling in the evening, solid areas exhibit a uniform temperature. But if there is an empty area beneath the surface, this can cause temperature fluctuations. The area identified by muography also showed heat anomalies, which is why the researchers brought in experts from Nagoya University in Japan to do muography.

The researchers are still doing muography within the Great Pyramid. They will have more data to release in the first few months of 2017.

Listing image by Scan Pyramids Mission