Interview with Professor Matt Griffin of Cardiff University, UK, who leads the team behind SPIRE, the Spectral and Photometric Imaging Receiver, one of the three instruments on board the Herschel Space Observatory, the largest telescope ever launched into space.
SPIRE and Herschel’s two other instruments, HIFI and PACS, are able to collect unprecedented images of the farthest galaxies thanks to Herschel’s 3.5-metre silicon carbide and aluminium mirror, which collects 20 times more light than any previous space telescope.
“To an experimental astronomer,” says Professor Griffin of the mirror, “it is a stunning technological achievement and to anyone with an appreciation of form and symmetry, it is an exquisite object.” Herschel sent back the first image of its four-year mission in September 2009, an amazing view of the M51, the ‘whirlpool galaxy’, taken by the PACS camera. Professor Griffin talked to us about the development of the telescope and his hopes for what it can achieve during its projected four-year mission.
Did the scientists who will be receiving data from Herschel, such as yourself, play any role in the design of the mirror?
In the early stages, myself and a number of other Herschel scientists were closely involved in specifying the requirements for the Herschel telescope. We also followed its design and manufacture very closely and we were influential in advising how it should be tested. This interest in the telescope development from start to finish shows how important it was to the success of the project.
How have the mirror and telescope performed since its launch?
Early Herschel results are showing that the mirror performs flawlessly and delivers to the instruments a beam of radiation from the astronomical source that matches exactly what was predicted, and what the instruments have been designed to accept. The outcome is a system that is beautifully in focus and which allows the most sensitive observations that we could have hoped for.
SPIRE contains an imaging photometer and an imaging spectrometer. How do the images that these meters capture differ?
The photometer is designed to make images at three different submillimetre wavelengths, analogous to taking pictures in different colours of visible light. These images will help tell us about the physics of regions in space where stars are forming by revealing such properties as the temperature, the mass, the energy output, and the properties of the dust out of which planets are eventually made.
The spectrometer will study the other material – the gas – from which stars form, by breaking up the incoming submillimetre light and analysing it to search for the signatures of particular atoms and molecules.
Is the calibration period of SPIRE now over?
Not yet. We are still in the ‘performance verification’ stage. So far the results are extremely encouraging, with the instrument and the telescope performing as expected or better. We are already able to make scientific observations with the photometer, and the spectrometer will be ready soon.
Are you pleased with the first images that you have received back from Herschel?
The early images and spectra that we have acquired so far are causing great excitement among astronomers. Although we have not yet finished setting up the instrument, the results show that Herschel will be able to fulfil its scientific promise.
Is there any particular galaxy, star, planet or phenomenon that you are aiming to capture?
One of the key science goals of Herschel is to study star formation in our own galaxy – to learn for instance, how solar systems like our own formed in the past by studying the same process that is going on in the galaxy today. Another is to study the way in which whole galaxies like our own formed and grew in the past – galaxy formation is of course star formation on a massive scale. By looking at very distant galaxies with Herschel, we can look into the past to see how the galaxies that now fill the universe came to be.