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100 Photographs in the Blink of an Eye

July 24, 2002

Scientists from the Universities of Sheffield and Southampton in collaboration with the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh have just opened a new window on the Universe by commissioning ULTRACAM - an ultra-fast camera which can take up to 1000 pictures a second in three different colours simultaneously. The camera, which is mounted on the largest optical telescope in Europe - the 4.2-m William Herschel Telescope on La Palma in the Canary Islands - has been designed to study some of the most rapid astronomical events.

Many people think of the sky as unchanging, so it may come as a surprise that astronomers wish to take pictures so quickly. In fact, high speed imaging is essential to study some of the most extreme astronomical sources in the Universe, including black holes, neutron stars and white dwarfs. These small but dense objects, representing the evolutionary end-points of the lives of stars, typically pack a few times the mass of the Sun into a volume only a few kilometres across. Their precise masses and sizes are not well known and very difficult to determine, but such information is crucial if we are to understand how stars age and die. In principle, it is possible to determine these parameters by observing eclipsing binary star systems, in which the black hole, neutron star or white dwarf sucks material from a larger companion star in orbit around it. The problem is that material in orbit close to the surface of a black hole or neutron star completes one orbit in about a millisecond (or about a second if the object is a white dwarf).

This is where ULTRACAM excels. By taking up to 1000 images a second in three different colours simultaneously, astronomers will now be able to study material in the innermost orbits around black holes, neutron stars and white dwarfs and observe how the light from these objects varies as the companion star obscures our line of sight to them. This allows a direct measurement of their masses, sizes and temperatures, enabling astronomers to test the fundamental physics which describes the extreme state of matter of which black holes, neutron stars and white dwarfs are made.

Dr Vik Dhillon, the ULTRACAM project scientist, remarks: "For the first time, astronomers have an instrument specifically designed for the study of high-speed astrophysics. Using ULTRACAM in conjunction with the current generation of large telescopes means that it is now possible to study high-speed celestial phenomena such as eclipses, oscillations and occultations in stars which are millions of times too faint to see with the naked eye."

ULTRACAM employs the latest in CCD detector technology in order to take, store and analyse data at the required sensitivities and speeds. CCD detectors can be found in digital cameras and camcorders, but the devices used in ULTRACAM are special because they are larger, faster and most importantly, much more sensitive to light than the detectors used in today`s consumer electronics products. Work started on the instrument during the summer of 1999, when the project was awarded £300,000 of funding by the UK`s Particle Physics and Astronomy Research Council. The project was completed on-budget and ahead of schedule in May 2002, when the instrument saw "first light" on the 4.2-m William Herschel Telescope on La Palma. As well as successfully commissioning the instrument, the project team also acquired the first scientific data on white dwarf stars, showing that the instrument is working to specification. The project team expect to obtain the first scientific results on the more demanding neutron stars and black holes during a second visit to the telescope in September 2002.

Particle Physics and Astronomy Research Council (PPARC)