Speaker
Description
If we want to look into the future it is sensible to look back to the past - at least as a starting point. A first approximation is to assume that the forward trajectory of a given technique would be a continuation of the past, but with more bells and whistles. Let's see where that might lead us when we think about where the technique of Stellar Intensity Interferometry SII might go. Let us reflect that the first and only purpose-built intensity interferometer was the one at Narrabri, conceived and built by Robert Hanbury Brown. In the half century that has passed since it was mothballed, a second such interferometer has not been built. Despite its undoubted success in observing stars with higher precision than before and also in overturning the understanding of photon physics, intensity interferometry sadly became a one hit wonder. Amplitude interferometry became the flavour of the month.
But now, despite heroic efforts, it is becoming clear that technological challenges are limiting what can be achieved with amplitude interferometry. It became clear some years ago that an opportunity for a revival of intensity interferometry was opening up. Perhaps surprisingly it has been the Cherenkov Telescope Array CTA project that has brought together a diverse group of astronomers wanting to explore the opportunities for SII. This resulted in the creation of the Intensity Interferometry Science Working Group under the umbrella of the CTA itself. Groups with access to IACT arrays (Imaging Atmospheric Cherenkov Telescopes) began to adapt these telescopes to carry out intensity interferometry studies. In parallel CTA managers were lobbied in a bid to include intensity interferometry as a science goal of the project. After 10 years there has been progress but it has still not happened. Whilst efforts must continue in this direction, the lesson surely is that if we are considering the longer time scale we must explore other avenues. By that I mean we must look beyond by a time equal to that of looking back to Narrabri. That would mean that we must look forward to 2075.
Therefore, if I stand back and look at the impressive progress that has been made with Intensity Interferometry up to now and attempt to divine where future progress can be made, I see a number of steps. One is to exploit the opportunity that is provided by becoming an additional scientifically productive and distinct science goal of CTA. The ultimate step in my field of view however would be to construct a second purpose-built intensity interferometer, one which builds upon the experience gained at Narrabri, VERITAS, MAGIC, HESS, ASTRI and of course CTA itself. An observatory built on a green field site (brown desert!) where the SII community itself will choose the parameters and determine its operational protocol. I will explore what the advantages of such a facility might be and what barriers need to be broached to realise it. My own vision, which is put forward to be knocked down and reimagined - a straw man - would be a 2000 telescope array with a footprint of 20 kilometers. I have been pursuing this idea for some years in a rather desultory fashion – it even has a name, SIITAR - but the current call for proposals from ESO can be a catalyst for a distinct group of intensity interferometry enthusiasts to campaign for such a facility in the longer future.
