Radio Eye on the Universe Gets Sharper|
by Rodney Steel
The largest submillimetre telescope ever built, the James Clerk Maxwell in Hawaii, is a major factor in maintaining Britain's pre-eminent position in international radio astronomy.
Its instrumentation has now been updated by the incorporation of the Submillimetre Common-User Bolometer Array (SCUBA), which can process observational data 10,000 times faster than before, and greatly enhances the capabilities of an instrument rightly regarded as one of the finest radio telescopes in the world.
The primary reflector is a 15 metre disc which reflects incoming radio waves back up to a 0.75 metre secondary so that they are re-reflected back down through an aperture in the primary reflector to a focus at the base of the instrument where recording and analytical instrumentation is located.
Distortion of the received radio wave emissions due to atmospheric disturbance and the action of gravity on the huge structure have to be reduced to the tiniest possible amount; during operation the parabolic shape of the primary reflector can be maintained to an accuracy of 25 microns (about the thickness of a thin sheet of paper). This guarantees efficient detection of signals with wavelengths as short as 0.3 mm.
The azimuth mount of the JCMT allows the instrument to be directed at any required point in the sky with an accuracy of 1/2000th of a degree - equivalent to the angle subtended by a full stop on this page at a distance of 57 metres.
Now scientists from all over the world can visit the JCMT and try to unravel the mysteries of the universe than can only be resolved by using the submillimetre and millimetre wavebands. This sect ion of the electromagnetic spectrum tells them about what is happening on cool objects such as planets, or in low-temperature clouds of interstellar gas where stars are forming.
In addition, far distant galaxies and the mysterious quasars (quasi-stellar objects, among the most distant and the most luminous objects known) are receding so fast from us that their infra-red emissions are shifted back down the electromagnetic spectrum into the submillimetre region.
The JCMT is a primary choice for astronomers wishing to study these remote objects at the furthest reaches of the known universe. James Clerk Maxwell was an eminent British scientist, born in Edinburgh in 1831, who graduated from Cambridge and later founded the famous Cavendish Laboratory there.
Among the projects to which the JCMT has made significant contributions are studies of the Sun, comets, molecular clouds, quasars, and the cosmic background radiation which is apparently a left-over remnant of the 'big bang' that is thought to have brought the universe into existence.
The JCMT has also been directed at areas of star formation that are obscured by the dense clouds of dust from which protostars initially condense. Submillimetre radiation escapes through these obscuring clouds even better than infra-red emissions and enables scientists using the JCMT to try and observe the birth of stars.
The search is on for pre-protostellar objects: condensations probably with a diameter no greater than that of the solar system and with a temperature still only 30 or 40 degrees above absolute zero.
"All of the theories indicate that you must go through this phase in the formation of a star," says Dr. Graeme White JCMT's British scheduler. "Nobody can tell you much about how a star forms out of a dust cloud. And after that we want to know what triggered off the initial collapse."
In fact, this galaxy is not just giving birth to a first generation of stars, as was presumed. The JCMT was able to discern gas that had already been heated by an earlier generation of stars, and what is now being observed is probably stars forming in the galaxy's disc.
Working on the JCMT today one of Britain's most is outstanding young astronomers, Dr. Jason Stevens. He is looking at galaxies called blazars, which have very active central nuclei emitting a wide variety of radiation. At their centre is probably a black hole, from the poles of which radio jets emerge directly along the line of sight from Earth, travelling at almost the speed of light.
In cooperation with astronomers in the United States and Finland, Dr. Stevens is to find out what powers these mighty jets, and why the emissions from blazars are so variable.
In 1997, astronomers are eagerly awaiting the arrival of a new comet, Hale-Bopp. Now still beyond the orbit of Jupiter, Hale-Bopp may be bright enough to be seen with the naked eye in daylight. To the JCMT it will be a dazzling object. And British astronomy is preparing to ride its slowing tail into the 21st century.
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