On top of the volcano – part two

By Matin Durrani at Sierra Negra, Mexico

Just as my Physics World colleague James Dacey mentioned earlier, neither of us felt super-wonderful yesterday visiting the Large Millimeter Telescope (LMT), which sits at a height of 4600 metres above sea level.  Spectacular though the facility is, the air pressure is roughly 60% of that at sea level and there is so little oxygen that even walking up a flight of stairs made me feeling pretty light-headed.

So, James and I were both quite glad to descend with LMT director David H Hughes to a height of 4100 metres, where it was time to visit another leading Mexican astronomy facility – the High-Altitude Water Cherenkov (HAWC) gamma-ray observatory.

Conditions here – despite being just 500 metres lower – are much more amenable and we were given a tour by Ibrahim Torres of the facility, which was officially opened in March this year. A collaboration between 26 Mexican and US institutions, HAWC consists of 300 detector tanks, which are each 4 m high, have a diameter of 7.3 m and are filled with 190,000 litres of extra-pure water.

Using four photomultiplier tubes in each tank, HAWC is designed to detect the “shower” of particles formed when high-energy cosmic rays strike the nuclei of gases in the Earth’s atmosphere. HAWC is expected to be 10–15 times more sensitive than its predecessor – the Milagro experiment in New Mexico.

HAWC is currently taking data, operating silently on the mountainside, with the only noise being the wind and the occasional truck bringing staff to the site. HAWC is not entirely isolated though: apparently rattlensakes, rabbits, lynx and the occasional coyote can be spotted or heard roaming around.

Find out more about HAWC in the video above, with Torres standing in the middle of the array. It looks quite a spooky place; in fact, part of a science-fiction movie has been shot here.