The James Clerk Maxwell Telescope

The James Clerk Maxwell Telescope (JCMT) is one of two telescopes operated by the Joint Astronomy Centre, the other being the United Kingdom Infrared Telescope (UKIRT).

The JCMT is the largest single-dish telescope in the world dedicated to detecting submillimetre radiation. Its 15-metre (50-foot) dish looks at the sky with instruments that tell us about the cold Universe in different ways. Operating between the infrared and radio waves, it uses some of the most sensitive and sophisticated instrumentation to detect the coldest material in the Universe, only a few tens of degrees above absolute zero. Water vapour in the Earth’s atmosphere intercepts this radiation, making the high and dry site of Mauna Kea vitally important for the research performed at the JCMT.

The JCMT's dish, as wide as a basketball court, collects the submillimetre light and feeds it to a set of sensitive detectors. The dish is protected from wind, sand and birds by a sailcloth-like membrane or Gore-Tex.

In between the stars are giant clouds where stars and solar systems are born. They are made of gas (mostly hydrogen) and cosmic dust (tiny particles of silicate and carbon). The clouds are some of the coldest objects in the Universe — so cold that their ‘heat glow’ is invisible to human eyes. We need specialised telescopes and instruments to see this submillimetre radiation.

The SCUBA camera took pictures showing the faint heat glow of interstellar dust grains. These fine particles, like soot or sand, are at temperatures below -400F. SCUBA itself was kept even colder than this, to improve its sensitivity. In its jacket of liquid helium it got down to less than a tenth of a degree above absolute zero, around -459.5F!

A map of the center of our Galaxy shows a complex region of shells, filaments, and clouds like cotton candy in the heart of the Milky Way. This exotic region lies 27000 light years from Earth, and our view of it in visible light is obscured by the intervening dust.

Far beyond our Milky Way, SCUBA saw galaxies more than ten billion light years away. These galaxies are enshrouded in dust at the edge of the universe, and tell us about star birth more than 90% of the way back to the start of time.

Closer to home, pictures of the dust around nearby stars provide tell-tale evidence for new planets around suns other than our own.

The gases and dust grains seen by the JCMT are not just important for the life cycle of stars. They are also the origin of all chemical elements heavier than Helium in the stars, clouds, planets, and in our own bodies. We are all made of stardust.

The JCMT also has 'heterodyne receivers' which detect light from gas molecules in space. These molecules emit characteristic submillimetre radiation patterns when they rotate. The patterns are 'fingerprints' that tell us about the temperature, density, or motion of the gas.

HARP is such an instrument which combines a camera and a spectrometer. This means we can learn about the chemistry of interstellar gas, its temperature, density and motion.

The nearest massive star formation to Earth is happening 1500 light years away in the constellation of Orion, the Hunter. In this cloud new stars are born, and into this stars disperse or explode as they die. HARP's images of Orion show the presence of carbon monoxide. The bright region in the center reveals new star formation. Evident is the surrounding gas undergoing streaming motions both to and away from the region.

The newest instrument on the JCMT is SCUBA-2 which will be the most powerful camera of its kind. New technology and novel design means it will map the sky 1000 times faster than its predecessor, SCUBA. This new instrument will keep the JCMT at the forefront of submillimetre astronomy, complementing the Submillimeter Array on Mauna Kea and forthcoming telescopes such as the Atacama Large Millimeter Array in Chile.

The JCMT is internationally funded, by the UK, Canada, and the Netherlands. It was opened in April 1987.

You can find some more technical information in a previous article about the JCMT.