Radio astronomy gets connected
25th May 2004
Member of the e-MERLIN team gather with representatives of Fujitsu Telecommunications Europe and Global Crossing UK to celebrate the start of work on the e-MERLIN fibre network. Sir Bernard Lovell, founder of the observatory, joins them by the Lovell Telescope
Work has started on the construction of an optical fibre network which will connect five radio telescopes to the giant 76-m Lovell Telescope at Jodrell Bank Observatory, operated by The University of Manchester in rural Cheshire. This e-MERLIN network will operate as a single radio telescope spanning 217 km, with unprecedented sensitivity provided by the enormous data rates carried by the optical fibres. The combination of high resolution due to the large separations and high sensitivity will make e-MERLIN a world-leading astronomical facility, continuing the pioneering spirit established by Sir Bernard Lovell over 50 years ago, and maintaining Jodrell Bank at the forefront of astronomical research well into the 21st century.
The network will use trunk fibres largely provided by Global Crossing UK with new fibre links from each telescope to the trunks being constructed by Fujitsu Telecommunications Europe. The total data rate carried by the network will be a continuous and sustained 150 Gb/s - about five times the total UK public internet traffic. Finding a way to provide a data network of this capacity on a national scale, reaching out to rural telescope sites, within the very limited project budget has been the largest challenge facing the e-MERLIN project. Astronomers and engineers at Jodrell Bank are delighted to have found a technical and commercial solution which meets their needs.
The MERLIN network was first established in 1980 and is now operated as a national facility by the University of Manchester on behalf of the Particle Physics and Astronomy Research Council. It combines radio telescopes near Cambridge, Worcester and Oswestry with two telescopes in Cheshire as well as the Lovell Telescope. Radio arrays like MERLIN produce detailed radio images of stars and galaxies. MERLIN's strength has been the high resolution provided by its 217-km span - it is the only telescope on the ground which can routinely provide images with as much detail as the Hubble Space Telescope but at radio rather than optical wavelengths. However, its sensitivity has been limited by the present connections from the remote telescopes to Jodrell Bank.
The locations of the e-MERLIN telescopes to be linked by fibre optic cables
The 76-m Lovell Radio Telescope
By linking the telescopes with optical fibre, the capacity of these connections will be increased by a factor of more than 100 and together with the newly resurfaced Lovell Telescope and improved receivers at each telescope, e-MERLIN's sensitivity will be boosted by more than a factor of 30, guaranteeing a wealth of new discoveries as astronomers from the UK and around the world use it to zoom in on distant stars and galaxies.
Dr Simon Garrington, project manager for e-MERLIN explained: "In an array like MERLIN, the network which transports the data is performing the same function as the curved dish of a single large radio telescope, bringing the radio waves to a common focus. With our present links, we are only able to transport less than half of one percent of the signal collected by our new receivers to the correlator at Jodrell Bank but with the new fibre network we will be able to transport an entire 4 GHz band back to Jodrell."
Prof Philip Diamond, Director of MERLIN, said: "Radio astronomy is crucial to the understanding of our universe because radio waves penetrate the clouds of cosmic dust and gas that hamper observations with optical telescopes. Our deepest observations with existing instruments have given us glimpses of distant galaxies in the process of formation and we are confident that e-MERLIN will reveal a radio sky teeming with such galaxies, any one of which we will be able to study in detail."
Roshene McCool, the fibre-optic engineer at Jodrell Bank who is designing the transmission equipment for the network said: "The fibre network provided by Fujitsu and Global Crossing allows us to use transmission equipment and protocols which we have developed with colleagues around the world specifically for radio astronomy data."
Phil Metcalf, managing director of Global Crossing Europe, said: "The high-capacity backbone linking the e-MERLIN array will give UK astronomers the networking platform they need to open up a new era of discovery."
Shigeyuki Unagami, managing director of Fujitsu Telecommunications Europe described the project as "a successful harmony of pioneering science, IT and telecommunications".
The e-MERLIN project has been jointly funded by The University of Manchester, The Northwest Development Agency (NWDA), the Particle Physics and Astronomy Research Council (PPARC), UMIST and The University of Cambridge.
To celebrate the start of work on the fibre network a reception was held today at Jodrell Bank Observatory with representatives from The University of Manchester, Global Crossing, Fujitsu and the funding partners.
Contact DetailsDr Simon Garrington, Jodrell Bank Observatory, firstname.lastname@example.org 01477 571321
Prof Phil Diamond, Jodrell Bank Observatory, email@example.com 01477 571321
Further Quotations from e-MERLIN StakeholdersProfessor Andrew Lyne, Director of Jodrell Bank Observatory, said, "This is an exciting time as the University of Manchester combines with UMIST to become a new premier research university. E-MERLIN epitomizes the world-leading initiatives which will be required to achieve this".
Chris Koral, NWDA Area Manager for Cheshire, said:,"Jodrell Bank represents a longstanding symbol of scientific endeavour in the Northwest and this is a great achievement which reaffirms its position at the leading edge of world astronomy. I am delighted that the NWDA has contributed to this important project, which will help to maintain the region's reputation for excellence in the future."
Professor Ian Halliday, Chief Executive of PPARC said, "With the upgrade to e-MERLIN, the UK's National Facility for radio astronomy has ensured that it remains at the forefront of international research, enabling UK astronomers to make important contributions to advancing our understanding of the Universe."
Professor Sir Martin Harris, Vice-Chancellor of the University of Manchester said,"This is very good news for Jodrell Bank Observatory and further strengthens its position at the forefront of astronomical research in the 21st century. The e-MERLIN project forms an important part of the work which goes on at the Observatory and the Lovell Telescope is a key element of the array which will benefit from the recent upgrades."
Notes for Editors
e-MERLIN Technical BackgroundThe maximum resolution of a telescope, be it optical or radio, is determined by its diameter divided by the wavelength. Since radio waves are typically 100,000 times longer than light waves, a radio-telescope would have to be of order 200km in size to equal the highest resolution achieved by optical telescopes. Building such a large single telescope is clearly impractical so the effect is achieved by linking together a number of telescopes spread over a large area and using the rotation of the Earth to "fill out" an effective aperture whose diameter is equal to that of the array. MERLIN, with an overall size of 217km, is the largest permanently connected array of this type in the world and the only one that can routinely image objects with a resolution comparable to that of the Hubble Space Telescope.
How MERLIN works.In an optical or single radio-telescope the waves falling on the surface are reflected to a common focus where they combine together to form an image. In MERLIN the individual telescopes form part of a giant surface and the signals received by each telescope are sent to a central correlator which forms the effective focus. The combined data are then used to make the image.
What determines the sensitivity of MERLIN?There are a number of factors which determine how faint an object can be detected: the number and size of the telescopes used, the sensitivity of the receivers at each telescope and the bandwidth of the links that return the signals to Jodrell Bank. The one area where it is possible to make a really substantial improvement is by greatly increasing the capacity of the links between the out-stations and Jodrell Bank - and this will be the key factor in the greatly increased sensitivity of e-MERLIN as compared to MERLIN. The inclusion of the upgraded Lovell Telescope into MERLIN - which effectively doubles the total collecting area and hence sensitivity - allied to improvements in the receivers will also play a significant role.
Linking the Telescopes to Jodrell Bank.Since its inception in 1980, the signals from each of the out-station telescopes have been brought back to Jodrell Bank over microwave radio links. Following an upgrade in 1992 these carry analogue data having a total bandwidth of approximately 30 MHz. However the receivers at the telescopes are capable of observations that simultaneously cover over 4 GHz of bandwidth, but most of this has had to be thrown away due to the limited bandwidth of the links - we can currently return only about 0.5% of the total data. The key element of e-MERLIN is to replace these microwave links with optical fibres that can carry vastly greater bandwidths. The maximum bandwidth in e-MERLIN will be 2 GHz in each of two polarizations. If the whole of this bandwidth can be used the amount of information that can be used to build up an image will increase by over 100 times.
The radio signals will be sampled adjacent to the low noise amplifiers at the focus of the telescopes and a total of 30 Gigabits per second will be transferred over optical fibre links to Jodrell Bank. The data will be modulated onto three "colours" of light, each carrying 10 Gigabits of data per second, carried by the fibre leaving each telescope.
At Birmingham the data from three telescopes, Cambridge, Defford and Knockin, will be consolidated onto one fibre whilst other fibres will carry the data from the telescopes at Darnhall and Pickmere. Finally at Jodrell Bank the data will be converted back into electrical form to be used in the data analysis. An optical transmission system specifically designed for radio astronomy applications has been developed at Jodrell Bank Observatory for this task.
There would be no point in bring back 30 Gigabits of data per second from each telescope if there was not a very powerful special purpose computing device, called a correlator, that could accept this amount of data and combine the signals from the individual telescopes. The correlator will need to process over 200 Gigabits of data per second! Such a correlator, using state of art digital circuitry, is now being designed and built at Penticton, British Columbia by the National Research Council of Canada.
The result, e-MERLIN.The use of optical fibres to carry the data back to Jodrell Bank coupled with the new correlator will give us an order of magnitude improvement in sensitivity. Allied with the use of the Lovell Telescope and improvements in the receivers an overall improvement in sensitivity of ~ 30 will be obtained. In order to get the fullest possible benefit of the sensitivity improvement that will be gained by the use of fibre-optic links, virtually all other aspects of the MERLIN system will have been either replaced or upgraded.
e-MERLIN will thus be an essentially new instrument - one of the most sensitive radio instruments in the world - capable of carrying out front rank research for many years to come.
e-MERLIN Science Summary
Introductione-MERLIN will be a general-purpose instrument capable of producing sensitive radio images of a wide variety of astronomical objects with a resolution which is very similar to optical images produced by the Hubble Space Telescope and future space and ground-based telescopes, such as the James Webb Space Telescope and the ALMA array in Chile. Like all of these major facilities, e-MERLIN will address a wide range of scientific questions. Some of these research programmes are being planned now and details are given below, but history has shown us that whenever we improve the observational capabilities of our telescopes by a factor of 10 - e-MERLIN represents a sensitivity boost of a factor of 30 - we discover new astronomical phenomena. It is almost invariably the case that the legacies of major telescopes are discoveries which could not be imagined at the time of construction. This is true of the Lovell Telescope, built in 1957 before the discovery of pulsars, quasars or black holes, and will undoubtedly be true for e-MERLIN.
Star-formation in the UniverseWhen did galaxies form the bulk of their stars? This is one of the key questions of current astronomy and involves careful observations of the most distant galaxies at a range of wavelengths including radio, sub-millimetre, infra-red and optical. Establishing a clear picture of the global star-formation history of the Universe is crucial to our understanding of how galaxies form and evolve and hence how their populations of stars and ultimately planets like Earth form. However, the large amounts of cosmic dust generated by early generations of massive stars obscures the view of even the most powerful optical telescopes. e-MERLIN will play a vital role here, because radio waves can penetrate this dust and the high resolution of MERLIN will allow the regions within these distant galaxies where star-formation is occurring to be mapped out. In somewhat closer galaxies, e-MERLIN can watch individual massive stars die in cataclysmic supernova explosions. These explosions and their remnants can tell us a great deal about the rate at which stars are born and die in different environments.
A MERLIN/VLA radio image at 1.4 GHz (shown as contoured radio brightness) overlaid on the optical image of the Hubble Deep Field from The Hubble Space Telescope. Although only the faintest of optical emission is detected at this position, this weak radio source is identified with a very red object and is thought to be a luminous starburst system close to the edge of the visible Universe with a redshift close to 4.4. The sensitivity and angular resolution of e-MERLIN at 5 GHZ will enable such object in the future to be studied in significant detail.
A false-colour radio image at 5 GHz of the nuclear region of the starburst galaxy M82 mapped with MERLIN and the VLA . This galaxy is around 10 Million light years distant and the nuclear region is ~3000 light years in extent. The compact objects are recent super nova remnants from massive stars made in the starburst which explode only a few Million years after formation.
Star-formation in the GalaxyCloser to home, in our own galaxy the Milky Way, high resolution radio observations with e-MERLIN will allow us to study the details of the formation of individual stars. There is a great deal we have yet to learn about this process and again the presence of cosmic dust in the turbulent clouds of gas where stars are born usually clouds the view of optical telescopes. One of the key questions here is the relationship between the young star, its surrounding disk of gas, destined to become planets, and the jets of gas squirted out at right angles to the disk. e-MERLIN will be used to study these disks and jets and aid our understanding of how stars and their planetary systems form.
Stellar activity and evolutionOur own Sun displays a well-known cycle of activity, manifested as sunspots, solar flares and coronal mass ejections. Some of these events have direct consequences on the Earth but the wider implications for the Earth's climate, for example, are subtle and a matter of great importance and debate. e-MERLIN will not be used to observe the Sun, but it will be used to observe a variety of active stars throughout the Galaxy to provide the broader picture of stellar activity. Radio emission is a characteristic of these active stars and e-MERLIN's high resolution will allow detailed studies to be made.