Posted on Monday 17th March 2014
University of Birmingham astrophysics are engaged in world-leading research into gravitational wave theory.
Here, Professor Alberto Vecchio, Professor of Astrophysics and Head of the Astrophysics and Space Research Group, in the School of Physics and Astronomy, explains the science behind the Big Bang announcement:
What are gravitational waves?
Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe, for example by the collision of two black holes, or by the cores of supernova explosions, or by the very early universe itself. Gravitational waves are emitted by accelerating masses much in the same way as radio waves are produced by accelerating charges – for example, such as electrons in antennas. These ripples in the space-time fabric travel to Earth, bringing with them information about their violent origins and about the nature of gravity that cannot be obtained by other astronomical tools. An indirect proof of the existence of gravitational waves has already been obtained by the American astronomers Russell Hulse und Joseph Taylor Jr. This won them the 1993 Nobel Prize in physics.
Why gravitational wave astronomy?
When in 1916 Albert Einstein predicted the existence of gravitational waves as an outcome of his General Theory of Relativity, he was convinced that these minute changes in the fabric of space-time would never be measurable. And still the direct detection of gravitational waves belongs to the most important open questions of modern science. Their direct observation will open the era of gravitational wave astronomy and will thus allow totally new insights into our universe – including clues as to its very beginning.
The direct observation of gravitational waves would have, aside from verifying once more the General Theory of Relativity, far-reaching consequences. It may become possible to cast an eye on the “childhood” of our universe. Up to now the observation of the sky is primarily limited to the electromagnetic spectrum (eg radio and X-ray telescopes and astronomy in visible light). The direct information thus available to us will reach back into the past only to an era as much as 380,000 years after the Big Bang: only at that time the universe became transparent for electromagnetic radiation. As a consequence, the various theories on the early universe have remained difficult to verify experimentally. The direct measurement of gravitational waves would open totally new possibilities, as gravitation is not subject to these limitations.
How to directly measure gravitational waves?
Gravitational wave detectors like LIGO, GEO600, and Virgo are L-shaped laser interferometers for high precision measurements. Each detector uses a laser split into two beams which travel back and forth down long arms in evacuated beam tubes. The beams are used to monitor the distance between precisely figured mirrors. According to Albert Einstein's 1916 theory of general relativity, the relative distance of the mirrors changes very slightly when a gravitational wave--a distortion in space-time produced by massive accelerating objects that propagates outward through the universe--passes by. The interferometers are constructed in such a way that they can detect a change of less than a thousandth the diameter of an atomic nucleus in the lengths of the arms relative to each other.
The first generation gravitational wave detectors like LIGO, Virgo and GEO600 are presently being upgraded to advanced configuration, by applying the newest components and technology. When the instruments go back online in late 2015, their sensitivity and frequency range will be significantly enhanced.
What is Advanced LIGO?
The Advanced LIGO Project is an upgrade in sensitivity for LIGO (Laser Interferometer Gravitational-wave Observatory). This represents a major upgrade that will increase the sensitivity of the LIGO instruments by a factor of 10, giving a one thousand-fold increase in the number of astrophysical candidates for gravitational wave signals. The new instrument once it reaches design sensitivity is expected to see gravitational wave sources on a routinely basis, with excellent signal strengths, allowing details of the waveforms to be observed and compared with theories of neutron stars, black holes, and other astrophysical objects moving near the speed of light.
The Advanced LIGO detector, currently being installed at the LIGO Observatories in Hanford, Washington, and Livingston, Louisiana, using the existing infrastructure, is expected to transform gravitational wave science into a real observational tool. The change of more than a factor of 10 in sensitivity comes also with a significant increase in the sensitive frequency range. This will allow Advanced LIGO to look at the last minutes of life of pairs of black holes as they spiral closer, coalesce into one larger black hole, and then vibrate becoming one. It will also allow the instrument to look for periodic signals from the many rotating neutron stars in our galaxy. Advanced LIGO will also search for the gravitational wave cosmic background, proving constraints on theories about the development of the early universe.
The LIGO Observatories were planned at the outset to support the continuing development of this new science, using the significant infrastructure. The upgrade involves state-of-the art lasers, optics and seismic isolation systems. Several of these technologies are significant advances in their fields, and have promise for application in a wide range of precision measurements, optics, and controls systems.
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