1-Mar-03 The James Clerk Maxwell Telescope: exploring the cold universe ============================================================== Douglas Pierce-Price What do you think astronomers look at? Many people imagine astronomers peering through the lens of an eyepiece at the stars, of which there are 100 billion in our galaxy alone. However, large modern telescopes don't have eyepieces, and instead display their images on computer screens. And what's even stranger is that some of these telescopes aren't used to look at stars at all! By looking at the stuff _between_ the stars, telescopes right here on the Big Island are answering questions about other worlds, the earliest galaxies, and the origins of the stars themselves. The James Clerk Maxwell Telescope (JCMT) on Mauna Kea is designed to detect "submillimeter radiation". This is light that is invisible to human eyes, with wavelengths of about a millimeter or less (from 1/25" to 1/100"). The JCMT is the largest single-dish submillimeter wave telescope in the world. Astronomers study objects so far away that their light has taken thousands or millions of years, or more, to reach us. This means that we are seeing these distant objects as they were thousands or millions of years ago, when the light first set out on its long journey. Unfortunately, after travelling so far, most of the submillimeter radiation is absorbed by water vapor in the Earth's atmosphere. This is why we need a high and dry site, to get above as much of the atmosphere and water vapor as possible. In fact, Mauna Kea is one of the best sites in the entire world for astronomy. At submillimeter wavelengths, we don't see the familiar hot and bright stars that you might expect. Instead, the submillimeter universe is the universe of the very cold - perhaps only a few tens of degrees above absolute zero (below about -400F). So what is out there that is so cold? One of the main things is the stuff between the stars - the interstellar medium. It is made up of clouds of gas (mostly hydrogen) and interstellar "dust" (very fine particles resembling soot or sand). The JCMT's 50-foot diameter dish collects faint cosmic signals, focussing them onto a set of incredibly sensitive detectors. Some measure radiation from gas molecules in space: fingerprints that pin down the temperature, density, and motion of interstellar clouds. Another acts like a camera, taking pictures with submillimeter waves. This is the "Submillimetre Common-User Bolometer Array", SCUBA. SCUBA uses ultra-sensitive thermometers called "bolometers" to see the heat glow of interstellar dust grains. The heart of SCUBA is cooled to a temperature less than one tenth of a degree above absolute zero (-459.5F), in what may be the coldest fridge in the world! Using this hi-tech arsenal of detectors, the JCMT studies the cold stuff that lies between the stars. The stars themselves are formed when a cloud of gas collapses under its own gravity, becoming dense and hot enough to start nuclear fusion in its core. At visible wavelengths the birth is hidden by the remaining material around the new-born star. However, we can use the JCMT to probe this cold cocoon and shed light on the mysteries of star formation. The constellation of Orion contains the closest sites of massive star formation, about 1500 light years from Earth (one light year is the distance light travels in one year, almost 6 trillion miles). The JCMT shows us ridges of gas and dust with denser knots of material where stars are about to be born. The light has taken about 1500 years to reach the telescope, so we see the clouds as they were 1500 years ago, shortly after the time the first settlers set foot on the Hawaiian Islands. Further from Earth, in the constellation Serpens, submillimeter waves let us peer inside vast cold columns of gas and dust in the Eagle Nebula. At their tips, SCUBA has detected dense cores which shield the rest of the columns from erosion by the intense ultraviolet radiation of hot, young stars. These imposing columns are 7000 light years from Earth, so we are looking back even further in time. The light we see from them today began its journey at the dawn of civilisation. As we look even further we can see the heart of our galaxy, the Milky Way. The Galactic Centre lies 27000 light years from Earth in the constellation Sagittarius. It is entirely hidden at visible wavelengths by the dense obscuring dust between us and the center. However, the JCMT reveals an exotic region where the interstellar medium is shaped by stellar winds, magnetic fields, and dying stars exploding as supernovae. At the very core of the Milky Way lies a giant black hole, more than one trillion times as massive as the Earth. Beyond our own galaxy, we can look at others. There are as many other galaxies in the universe as there are stars in our own galaxy - about 100 billion. The JCMT has seen distant galaxies whose dust hides them from telescopes that rely on visible light. These galaxies tell us about star formation in the very early universe, about 10 billion years ago, almost nine tenths of the way back to the start of time. Having "travelled" so far from Earth, we can now set our sights for home. But are there other Earths out there - planets around stars other than the Sun? For example, Epsilon Eridani is a nearby star just 10.5 light years away and similar to our Sun. Observations with the JCMT and SCUBA have shown that planets orbiting the star have cleared a hole in the surrounding dust, leaving tell-tale evidence for these elusive other worlds. So what does the future hold? The JCMT will complement the next generation of submillimeter telescopes, such as the Atacama Large Millimeter Array (ALMA) to be built in Chile. With newer, more advanced detectors we will continue to answer questions about the cold universe, from nearby worlds back to the start of time. To find out more about the James Clerk Maxwell Telescope, which is run by the Joint Astronomy Centre, please visit our website at http://outreach.jach.hawaii.edu/ Douglas Pierce-Price is the Science Outreach Specialist for the Joint Astronomy Centre in Hilo, which runs the James Clerk Maxwell Telescope and the United Kingdom Infrared Telescope.