100 Photographs in the Blink of an Eye
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.
Images and further information
Project web pages can be found at:
http://www.shef.ac.uk/~phys/people/vdhillon/ultracam
The following images are available from Gill Ormrod at PPARC on
01793 442012 or email gill.ormrod@pparc.ac.uk
[Image 1:
http://www.pparc.ac.uk/Nw/Press/2002_0519_162653AA.JPG (1.1MB)]
Close-up photograph of ULTRACAM mounted at the Cassegrain focus
of the 4.2-m William Herschel Telescope on La Palma.
[Image 2:
http://www.pparc.ac.uk/Nw/Press/xrb.jpg (79KB)]
An artist’s impression of an X-ray binary star, consisting of a
black hole (which lies at the heart of the accretion disc, at
the point where the jets originate) pulling material from a
solar-like companion star. This type of object will be one of
the main targets for study with ULTRACAM. Picture courtesy of
Dr Rob Hynes (University of Southampton).
The following ULTRACAM first-light images are available from
http://www.shef.ac.uk/~phys/people/pkerry/ultracam.html
[Image 3:
http://www.pparc.ac.uk/Nw/Press/m13.jpg (447KB)]
The globular cluster M13 in the constellation Hercules.
[Image 4:
http://www.pparc.ac.uk/Nw/Press/m51.jpg (333KB)]
Spiral galaxy M51 in the constellation Canes Venatici (the Hunting
Dogs).
Notes for editors
1.The Particle Physics and Astronomy Research Council (PPARC) is
the UK’s strategic science investment agency. It funds research,
education and public understanding in four broad areas of
science — particle physics, astronomy, cosmology and space
science.
PPARC is government funded and provides research grants and
studentships to scientists in British universities, gives
researchers access to world-class facilities and funds the UK
membership of international bodies such as the European Laboratory
for Particle Physics, CERN, European Space Agency and European
Southern Observatory. It also contributes money for the UK
telescopes overseas on La Palma, Hawaii, Australia and in Chile,
the UK Astronomy Technology Centre at the Royal Observatory,
Edinburgh and the MERLIN/VLBI National Facility.
2. The UK Astronomy Technology Centre is located at the Royal
Observatory, Edinburgh (ROE). It is a scientific site belonging
to the Particle Physics and Astronomy Research Council (PPARC).
The mission of the UK ATC is to support the mission and strategic
aims of PPARC and to help keep the UK at the forefront of world
astronomy by providing a UK focus for the design, production and
promotion of state of the art astronomical technology. The Royal
Observatory, Edinburgh comprises the UK Astronomy Technology
Centre (UK ATC) of the Particle Physics and Astronomy Research
Council (PPARC), the Institute for Astronomy (IfA) of the
University of Edinburgh and the ROE Visitor Centre.
3. The 4.2-m William Herschel Telescope (WHT) is operated on the
island of La Palma in the Canary Islands in Spain by the UK’s
Particle Physics and Astronomy Research Council, its Dutch
equivalent, the NWO and the Spanish Instituto de Astrofisica de
Canarias (IAC).
4. White dwarf: A late stage of stellar evolution for stars of
up to about 1.5 times the mass of the Sun. A white dwarf is
formed when such a star exhausts its sources of fuel for nuclear
fusion and collapses under its own gravity to a highly compressed
and very dense state. Stars of greater mass become even denser
neutron stars or black holes. White dwarfs have no internal
source of energy and so gradually cool into dead, inactive
stellar relics called black dwarfs.
5. Neutron star: A compact, extremely dense star composed almost
entirely of neutrons. They are formed when stars between about
1.5 and 3 times the mass of the Sun run out of nuclear fuel,
explode as a supernova and then collapse under their own gravity
to a very dense state in which protons and electrons fuse to
form neutrons. More massive stars collapse even further and
become black holes. Less massive stars collapse to become white
dwarf stars.
6. Black hole: A region of space surrounding an extremely dense
concentration of matter, in which the gravitational force is so
strong that matter and energy cannot escape from it.
7. Why does ULTRACAM produce photographs in 3 colours
simultaneously?
The reason is that the material at different temperatures will
emit radiation in different colours, and hence by observing the
variability in the 3 colours simultaneously different regions of
the object can be probed (this also gives a crude idea of their
temperature). The 3 colours have to be simultaneous as if taken
sequentially there is the problem of the object varying between
the exposures of the different colours.
