OAS Society Talk ~ July 2021 ~ Dr Matthew Bothwell
A report by Andrew Ramsay
It is not often that members of the OAS are startled by a new branch of astronomy. Last month’s evening talk was an exception.
Introducing the science of bolometry, speaker Matt Bothwell explained how the inventor of the bolometer, a device for detecting ultra-long wavelength radiation, had first demonstrated it by pointing it at a cow. Ultra-long wavelengths are also, confusingly, called sub-millimetre wavelengths, and they lie between visual and radio waves – basically infrared. Samuel Pierrepoint Langley’s late 19th century invention had sensed the warmth of a cow standing 400 metres away.
However the bolometer mainly remained as a “one-pixel camera” curiosity until the early 1990s when the developing applications of very sensitive temperature dependent resistors (thermistors) meant that the components could be shrunk. Images were still pretty fuzzy until the opportunity to use supercooled detectors emerged. With these each detector could be utilised as a tiny switch – just like the individual cells of a CCD camera. The era of the SCUBA (Sub-millimetre Common User Bolometer Array) had arrived.
Armed with this device astronomers started to search the skies for infrared emitting objects. An application developed by Dr Bothwell and his colleagues was to hunt for distant galaxies. A surprising property of infrared-emitting galaxies is that the standard inverse square rule for intensity of radiation appears to break down. What is in fact happening is that red shift moves the peak of the spectrum curve towards the sub-millimetre band. In effect the farther the galaxy is away from us, the more intense the radiation in this band.
Dr Bothwell explained that this had enabled astronomers to solve one of the mysteries of the cosmology – the existence of giant galaxies no longer making stars, with no indication of their origins. “SCUBA-diving astronomy” could identify their precursors as major sub-millimetric emitters appearing in the early stages of the universe – the edge of the universe. No restaurants were found, however.
(With apologies to Douglas Adams and thanks to Matt Bothwell for an inspiring talk)
Matt Bothwell’s book The Invisible Universe is published by One World Publications.