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The Royal Society of Edinburgh

Robert Cormack Bequest Lecture 2008

Professor Michael Garrett, General Director, ASTRON

28 April 2008

100 Years of Radio Astronomy: Past, Present and Future

On 28 April a packed audience in the Royal Society of Edinburghs main lecture theatre wasprivileged to hear a fascinating talk on the history of Radio Astronomy. This years Robert CormackBequest lecture was given by Professor Mike Garrett, Director of ASTRON, the NetherlandsInstitute for Radio Astronomy, which collaborates extensively with observatories and universities inBritain.

Professor Garretts lecture formed the finale of the annual Cormack Meeting, organised for andattended by astronomers from across Scotland. The meeting itself was crammed with high-quality

talks, the majority given by students. The topics covered included observational and theoreticalwork on the Sun and the Solar System, the discovery of a planetary system similar to our own, thegas between the stars, the nearby Andromeda galaxy, gravitational lenses (light can be focused bygravitational fields), and surveys on how galaxies cluster together and what that implies forcosmology. Those present even heard about work on alternative descriptions and theories ofgravity, which attempt to solve some long-standing problems with Einsteins theory of GeneralRelativity.

Two prizes were awarded: Garry Angus of St Andrews University won the Postgraduate Prize for atalk entitled On the proof of dark matter, the law of gravity and the mass of neutrinos. TheUndergraduate Prize was won by Laura Porter of Glasgow University, for her talk CometaryImpacts with the Sun.

Professor Garretts Cormack Lecture was entitled One Hundred Years of Radio Astronomy: PastPresent and Future. He began with the startling news that, although he was born in Scotland and isa graduate of Glasgow University, he had never given a talk in Scotland and indeed had neverbefore delivered a public lecture. 0ne would never have guessed the latter, for his talk wasfascinating, accessible and rich with history: he brought the past to life with whimsical details of thelandmark events and dramatis personae, told of radio astronomys most exciting discoveries, andeven touched on the possibility of detecting radio signals from other intelligent species.

Professor Garrett introduced his topic by setting out the scale of the Universe, from the SolarSystem to the most distant things that can be observed. He pointed out that the travel time of light(of which radio radiation is a form) means that the further away we look, the more deeply we reachinto the past. The relatively long wavelength of radio waves also means we are looking at very

large structures (rather than at atoms or molecules), material at temperatures close to absolutezero, and objects that are radiating by exotic, high-energy mechanisms utterly unlike the thermalradiation coming from our own Sun. Radio astronomy has provided a unique and very differentview of the Universe.

He began with a look at the roots of radio astronomy, which was an outgrowth of the desire tounderstand and abolish various mysterious sorts of static that might interfere with the newtechnologies of radio and telecommunications. In 1932 Karl Jansky, working at the Bell TelephoneLabs in New Jersey, discovered a signal that repeated once every 24 hours. He quickly realised itmust originate beyond the Earth and probably from the centre of the Galaxy and reassured usthat it was not likely to come from an intelligence trying to communicate!

When the electronics engineer and amateur radio enthusiast Grote Reber heard about Janskysdiscovery, he built the worlds first radio telescope, in 1937. He realised that to understand themechanisms producing the signal detected by Jansky, one must look at different frequencies. Hebuilt a detector that could look at very low frequency (long wavelength), and to his shock he found

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that instead of getting ever weaker as the frequency dropped (as it would in a thermal object suchas the Sun), the radio signal coming from the Galaxy got much stronger. This was the birth of awhole new area of astrophysics, which has led to dramatic discoveries about the Universe. Radioastronomy has been the topic of six Nobel Prizes.

Professor Garrett mentioned some of Rebers other projects, which made him something of aneccentric in his day, but which we would now say were visionary. For example, he built one of the

worlds first solar-heated houses, and also designed, built and drove an electric car known asPixie.

Shortly before World War II, the British astronomer Bernard Lovell began working on cosmic raysin the atmosphere. But having taken his detector to a hilltop one day, he was picked up by theMinistry of Defence and commandeered to develop radar for the detection of enemy aircraft. Afterthe War he moved to Jodrell Bank, near Manchester, where he built a fixed radio telescope withwhich, in 1949, Robert Hanbury Brown obtained the first radio map of another galaxy theAndromeda spiral. Later, Lovell built the now-famous steerable radio telescope at Jodrell Bank, stillthe third-largest steerable dish in the world.

By the late 1950s, financial support for Jodrell Bank had sharply declined. But it was about to do itsbit for the Cold War. A transfusion of new funds flooded in when the Soviet Sputnik satellite waslaunched in 1957, sparking fears in the West about possible missile attacks and galvanisingWestern governments into ensuring they could detect them, if launched. The telescope was rapidlyadapted and was able to detect Sputniks booster rocket. Bernard Lovell went on to detect theMoon landings of two Soviet satellites. The telescope even intercepted the first-ever picturetransmitted from the surface of the Moon while it was being transmitted from Luna 9.

In those days of distrust and suspicion, Professor Garrett told us that Jodrell staff with Communistsympathies were carefully monitored by MI5. During the Cuban Missile Crisis of October 1962, thetelescope was again diverted from its astronomical observations to point eastwards. In the event ofan ICBM launch towards the UK it could have provided a seven-minute warning, saving millions oflives.

Radio astronomy was advancing at a meteoric pace, and observers were seeking ways of seeingfiner detail in astronomical objects. How small a feature can be made out in an image is governedby the size of the telescope. But the Jodrell Bank dish was already as large and heavy asengineering could make it and the need to make a larger telescope stimulated British astronomerMartin Ryle by a brilliant piece of lateral thinking to invent the technique of aperture synthesis,for which he won a Nobel Prize.

By placing two or more telescopes some distance apart, and then adding their received signals in acomputer, a much larger telescope can be simulated, which can then measure the size and shapeof very small structures. This was done at Jodrell Bank by driving a second, mobile telescopearound the Cheshire countryside, and it was found that pub car parks proved as good a place asany to perform observations! Aperture synthesis is a form of interferometry, so named because of

the way the signals are added together to create a picture.

Interferometry led to the discovery of some tiny, very bright astronomical radio sources, but no-oneknew what or how far away they were: were they truly small and nearby or enormous and verydistant? By a remarkable coincidence, shortly afterwards, the passage of one of these sourcesbehind the Moon allowed it to be identified as a faint blue star. When this star was observed withan optical telescope, one of the most exciting discoveries in the history of astronomy was made:that these star-like radio sources were immensely distant and extremely powerful objects ofunknown kind. They were soon dubbed quasi-stellar objects, for they could not possibly be stars.It is now known that these quasars are powered by super-massive black holes.

Another new class of astronomical object came to light in 1968, during observations to find outwhether quasars twinkle like stars. Tony Hewish and research student Jocelyn Bell found an objectthat beamed radio waves in pulses, and wondered at first whether theyd detected a signal from analien intelligence! These are the now-famous pulsars, the dead remnants of exploding stars,rotating like abandoned, gradually-slowing lighthouses as they cool and fade. Mike let us hear the

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recording of a very young pulsar, spinning so fast that when translated into audio form its signalsounds like a high-pitched squeal.

One of the most exciting discoveries of radio astronomy is the realisation that a large fraction of theenergy observed in the Universe is released from strong gravitational fields rather than by nuclearfusion that lights the Sun and the stars. The central parts of active galaxies are often powered bygravity, not nuclear fusion.

Professor Garrett closed by talking briefly about some of the exciting new radio telescopes nowbeing designed or constructed: LOFAR (the LOw Frequency ARray), based in the Netherlands,and SKA (the Square Kilometre Array), to be built in Australia and South Africa.

LOFAR is an interferometer, but it is one unlike any other. It is an array not of individualtelescopes, but of simple antennae. Because an antenna is relatively cheap, a great many of themcan be bought and distributed over a very large area, simulating a much bigger telescope, asbefore. Construction of the LOFAR array, with a diameter of 350 kilometres, is well under way; itwill eventually have 25000 antennae. LOFAR is also set to expand across Europe, with stations inthe UK, Germany, Sweden, France and Italy expected to be built in the next few years.

SKA is still in the design phase. It will probably be a hybrid array of individual antennae andconventional radio telescopes, with a total area of one square kilometre 50 times larger thananything we have today. SKA is expected to be operating in about seven years time.

Both of these new telescopes will be able to look at extremely fine details in radio sources, and areexpected to reveal features never seen before. SKA will be able to detect the leakage radiation(from television and telecommunications) emitted by any Earth-like civilisations in the Sunsvicinity. But more importantly, they will be able to see the dawn of the Universe, the time whenhydrogen first started to condense into the structures from which galaxies were formed. Theypromise to reveal secrets about the form and evolution of the Universe, and to cast light on someof astronomys greatest puzzles. The next decade will be an exciting time for radio astronomers!

Professor Garretts talk stimulated lots of questions. How do you synthesise a circular aperture

when all you have is two telescopes? He explained that the imaginary line joining the telescopessweeps out a circle on the sky as the Earth rotates. Are China and India doing radio astronomy?Professor Garrett replied that both countries are involved with SKA. China is building its owntelescope, FAST, and is sending lots of high-quality research students to study in UK universities.Astronomy is excellent at attracting young people all over the world into science. He said heconsidered it very important not to close down the recently-upgraded Jodrell Bank telescope, whichwould severely impact Britains participation in SKA and its reputation as a world leader inastronomical research.

How common is life in the Universe? This simple but profound question launched Professor Garretton a fascinating mini-talk. He pointed out that more than 10% of stars have planets, so in ourGalaxy alone we can expect perhaps ten billion solar systems. Predicting how many have life (let

alone intelligent life) is much more difficult, as first realised by the astronomer Frank Drake almost50 years ago. It is perplexing that we havent detected signals from any intelligent species, whopresumably are also trying to contact other civilisations. Professor Garrett said he thinks microbiallife is probably common, but intelligent life rare. Alternatively it could be that civilisations aretransient, or their technological phase short-lived. He talked about SETI, the Search for Extra-Terrestrial Intelligence, saying how important it is to ensure it continues to be funded. Are wesendingsignals? Professor Garrett replied that we are not, in general, although occasionally this isdone as a public relations exercise to stimulate funding. However, other civilisations would be ableto detect our leakage radiation from television signals and military radar operations.

Alison Campbell

Opinions expressed here do not necessarily represent the views of the RSE, nor of its Fellows

The Royal Society of Edinburgh, Scotlands National Academy, is Scottish Charity No. SC000470