Press Release - Scientists weigh ingredients in recipe of the Universe
An international team of scientists from Cambridge, Manchester and
Tenerife has released the first results of new high-precision
observations of the relic radiation from the Big Bang, often called
the cosmic microwave background or CMB.
These observations have been made with a novel radio telescope called the
Very Small Array (VSA) situated on Mount Teide in Tenerife. The images
show the beginnings of the formation of structure in the early Universe.
From the properties of the image, scientists can obtain vital information
on just what happened in the early universe and distinguish between
competing cosmological theories.
Intruigingly, when combined with existing information on the CMB, they
seem to show just how much the growth of the Universe itself (and of structures
in it) is controlled by matter and how much by the mysterious dark energy
that is now thought to pervade the vacuum of space.
The VSA telescope works by being able to detect very faint variations in
the temperature of relic radiation, the radiation left over from the Big
Bang.
Today we can see this radiation in all directions on the sky at a
temperature of just three degrees centigrade above absolute zero, giving a
picture of the Universe when it was just one 50,000th of its present age.
Because galaxies must have formed out of the primeval fireball,
astrophysicists have predicted that their seeds will have left imprints in the
radiation. Across the sky, there should be tiny variations in the
temperature of the relic radiation. However these are very weak - only one
10,000th of a degree centigrade.
During its first year of operation the VSA has observed three patches of
sky, each some 8 x 8 degrees across. It can see detail down to one third
of a degree, well matched to the typical size of interesting temperature
variations.
The VSA has 14 aerials, each similar to a satellite TV dish but only 15 cm
across. The signals from each aerial are combined, forming an
interferometric array - a technique pioneered by Cambridge physicists.
The array is able to filter out unwanted terrestrial and atmospheric
radiation allowing the the extremely faint CMB sky signal common to all
the aerials to be detected. This approach allows high precision
observations to be made at modest cost - the capital cost of the VSA was
£2.6 million.
The performance of the VSA also results from using advanced receivers
built at Manchester University and from the outstanding atmospheric
conditions at the 2.4 km high Teide Observatory on Tenerife. The VSA can
therefore measure specific, individual structures in the relic radiation
with great precision.
A small number of other experiments have made similar observations. The
different experiments work in different ways and face different challenges
and sources of error; a key advantage of this diversity is that if their
results agree, one can be confident that they are correct. One special
strength of the VSA is that it is an interferometer array; another is that
it is able to robustly remove the contaminating radiation from
radiogalaxies and quasars that lie between us and the CMB relic radiation.
The VSA results provide amazing confirmation of the current picture of the
Universe.
Notes for Editors
Images and Web Sites
Images and captions, and links to the scientific papers, are available from
the Cavendish Laboratory website at
http://www.mrao.cam.ac.uk/telescopes/vsa
See also:
Press release in both English and Spanish at the Instituto de Astrofisica de
Canarias website:
http://www.iac.es/gabinete/noticias/2002/m05d23.htm
The Jodrell Bank website:
http://www.jb.man.ac.uk
The PPARC website:
http://www.pparc.ac.uk/Cnt/CM.asp
The VSA is a collaborative project between the Astrophysics Group at Cambridge
University's Cavendish Laboratory, Manchester University's Jodrell Bank
Observatory, and the Instituto de Astrofi'sica de Canarias (IAC) in
Tenerife. The project is funded by the UK Particle Physics and Astronomy
Research Council and the IAC.
Background notes
The cosmic microwave background
The cosmic microwave background radiation was discovered in 1965 by American
physicists Arno Penzias and Robert Wilson (who received the Nobel Prize for
the work). It is a faint radio radiation which fills the entire universe, and
thus appears to come from all directions in the sky. It is believed to be the
relic of the hot Big Bang phase of the universe, when the entire universe was
roughly the temperature of the surface of the Sun. The expansion of the
universe has since cooled the radiation down to a temperature of just under 3
degrees above absolute zero (ie -270 deg C). There are tiny variations in this
temperature, of a few parts in 100,000, which were first discovered by the
NASA satellite COBE in 1992. These are due the tiny fluctuations in density of
the universe which have since collapsed under gravity to form all the
structures (galaxies and stars) in the universe. These density fluctuations
are believed to be quantum fluctuations, blown up to astronomical size by a
process in the very early universe called 'inflation'.
The power spectrum of the cosmic microwave background
Astronomers describe the fluctuations in the cosmic microwave background by
its power spectrum. This is a graph of the strength of the fluctuations versus
their angular size. Theories of the universe can predict the shape of this
graph in detail, and the theories are tested by comparing the observed power
spectrum to the predictions. An important prediction of the favoured class of
theories, based on the theory of inflation, is that the power spectrum should
show multiple peaks. These are due to coherent oscillations (sound waves) in
the hot plasma of the early universe, driven by quantum fluctuations that had
been vastly enlarged by the process of inflation.
Flatness of the Universe
Einstein proposed in his General Theory of Relativity in 1915 that
matter and energy cause space to become curved. In curved space
geometry works differently to normal flat (Euclidean) geometry: the
angles of a triangle don't add up to 180 degrees. Einstein showed that
the curvature of the entire universe depends on the amount of matter
and energy in it. If there is relatively little matter/energy, the
universe is negatively curved (like the surface of the bell of a
trumpet or the stem of a wine glass). If there is a lot of
matter/energy, space is positively curved (like the surface of a ball)
- this also means the universe is finite in size. If the amount of
matter/energy is just right, space is flat, and traditional school
geometry does apply. Observations of the the CMB measure the curvature
of space by effectively constructing a triangle between the observer
and the edge of the observable universe, and measuring its
angles. These measurements are showing that space is indeed flat.
Dark Matter and Dark Energy
Astronomers have long known that there must be another type of matter in the
universe besides the ordinary matter that the stars and planets are made
of. This matter is detected by its gravitational effects, but what form it
takes is a mystery; some type of new heavy subatomic particle is usually
assumed, and given the name dark matter. Einstein's General Theory of
Relativity also allows for the existence of dark energy (also called the
Cosmological Constant). This is a property of empty space that causes the
universe to expand more and more rapidly. Long thought to be a mathematical
curiosity, it now turns out that the dark energy is real; the accelerating
expansion was discovered in the last few years by observations of distant
supernovae. Now the observations of the CMB have confirmed this. Both dark
matter and dark energy contribute to the flatness of the universe, but the
amount of dark matter can also be measured by combining the CMB measurements
with measurements of the Hubble Constant (the expansion rate of the
universe). There is not enough dark matter to make the universe flat, so there
must be a contribution from dark energy too. The nature of the dark energy is
not at all understood.
Contact details
For more information please contact any of these staff or research students
Dr Keith Grainge (Cambridge, +44 1223 337298, kjbg1@mrao.cam.ac.uk)
Dr Richard Davis (Manchester, +44 1477 571321, rjd@jb.man.ac.uk)
Prof Rafael Rebolo (IAC, +34 922 605273, rrl@ll.iac.es)
Dr Mike Hobson (Cambridge, +44 1223 339992, mph@mrao.cam.ac.uk)
Prof Rod Davies (Manchester, +44 1477 571321, rdd@jb.man.ac.uk)
Dr Mike Jones (Cambridge, +44 1223 337363, mike@mrao.cam.ac.uk)
Jose Alberto Rubino-Martin (IAC, +34 922 605370, jalberto@ll.iac.es)
Dr Richard Saunders (Cambridge, +44 1223 337301, rdes@mrao.cam.ac.uk)
Clive Dickinson (Manchester, +44 1477 571321, cdickins@jb.man.ac.uk)
Dr Bob Watson (Manchester, working at IAC, +34 922 605276 raw@ll.iac.es)
Rich Savage (Cambridge, +44 1223 337234, rss21@mrao.cam.ac.uk)
Anze Slosar (Cambridge, +44 1223 337278, anze@mrao.cam.ac.uk)
Angela Taylor (Cambridge, +44 1223 337304, act21@mrao.cam.ac.uk)
Prof Anthony Lasenby (Cambridge, +44 1223 337293, anthony@mrao.cam.ac.uk)
Dr Paul Scott(Cambridge, +44 1223 337306, paul@mrao.cam.ac.uk)
Klaus Maisinger (Cambridge, German speaker, +44 1223 337366, maising@mrao.cam.ac.uk)
Dr Ruediger Kneissl (Cambridge, German speaker, +44 1223 337298, rkneissl@mrao.cam.ac.uk)
Kieran Cleary (Manchester, +44 1477 571321, kcleary@jb.man.ac.uk)
Ian Morrison (+44 1477 571321, im@jb.man.ac.uk)
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