How is LOFAR different to other telescopes?
LOFAR is opening up a new window on the electromagnetic spectrum (30‑200 MHz) that is essentially unexplored at these sensitivities and resolution. In addition, it offers a huge field of view ‑ important in terms of survey speed but also in terms of investigating the transient radio sky. It is transformational in terms of technology ‑ no moving parts ‑ sometimes referred to as the first "software" telescope. The LOFAR approach is to deploy a huge collecting area made up of inexpensive dipoles but with a clever back end that uses advances in digital electronics to form multiple telescope beams, steering them from one point on the sky to another instantaneously.
Is the technology up to the task?
Yes, the technology has been shown to work well during the commissioning phase. A more important aspect for LOFAR is whether the software is up to the task. This has to deal with fluctuations in the incoming signals due to ionospheric disturbances ‑ these change quickly in time but also spatially on the sky and within the field of view. So this is the real challenge ‑ implementing the next generation of radio astronomy software algorithms that are needed to calibrate the data.
How much did LOFAR cost?
The total cost were 100 Million euro ‑ that includes telescope hardware, ground, infrastructure, some R&D and some software development (but not all).
How will LOFAR change radio astronomy?
The transformational technology is one way, the size of the data sets generated, is another ‑ we produce so much data we can only store it for a few weeks. That means we have to process the data automatically via a pipeline and then delete the original raw data (keeping only averaged uv‑data). In the past, astronomers would spend inordinate periods of time playing with data ‑ that is no longer possible. The same will be true of the Square Kilometre Array (SKA: a new generation of radio telescopes to be built, see also www.skatelescope.org
) and the software we are producing for LOFAR will be needed if the SKA is to achieve dynamic ranges of 10^7.
What has been the greatest technical/logistical challenge?
The biggest challenge has been to roll the telescope out ‑ LOFAR has about 45 stations ‑ each is as big as a football field and they all need land, power, & fibre connections to the BlueGene supercomputer of the University of Groningen. With eight international stations, the scale of the problem also has a European dimension. We've had a few setbacks in the roll‑out (cold winters) so we've only had the spring/summer/autumn to deploy stations and during this period we have also had set backs because we could not build during the bird breeding season. In the latter case, we negotiated with the local authorities and bird societies and could do some work provided we had various safeguards in place for ground nesting birds.
What big science questions will LOFAR answer?
Astronomers hope that LOFAR will detect the signature the epoch of reionisation. If it does then this will open up an area of study in astronomy that will be even bigger than the cosmic microwave background (CMB). The latter looks at a single epoch in the history of the evolution of the Universe ‑ the EoR refers to a much longer period of time ‑ from the so‑called dark ages to the generation of the light from the first stars and galaxies or whatever it was that was around in these times.
Once LOFAR has detected the EoR signature, you can be sure that even larger low‑frequency telescopes will be constructed in order to do topography of the EoR ‑ we will see how the first large‑scale structures in the Universe began to evolve over time in the early Universe.
Do you envisage any unique or innovative science done with LOFAR?
Perhaps the innovative science (but see also above) is using LOFAR as something that goes beyond astronomy ‑ one of the key science programmes is the detection and location of cosmic ray events, for example. The LOFAR infrastructure itself is also being used to do geo‑physics and precision agriculture. The field‑of‑view provided by the telescope is going to make it a fantastic discovery instrument ‑ an example is SETI surveys ‑ they are currently limited by the amount of sky they can see ‑ the usual needle in the haystack problem. LOFAR will change that ‑ if there are low‑frequency beacons out there, we will detect them.
How will LOFAR help in the development of the Square Kilometre Array?
In many ways, for example with respect to data rates, software, developing the science case (e.g. Epoch of Reionization (EoR)) but also its the first mass‑produced telescope ‑ LOFAR is not some huge steel "one‑off" parabola made by one big company ‑ its all about system integration with thousands of elements being put together to make up one huge telescope. For example, there are 25,000 dipoles in the high‑band antenna system alone ‑ there is a huge experience built up in tendering for these kind of large procurement projects. The SKA will face even larger challenges with respect to procurement and system integration.