14 DAY TRIAL // Since the 1930's it has been apparent that the Universe is made up of more than just the things we can see. It is now widely accepted that a large fraction of the Universe consists of "dark matter" in the form of a new type of fundamental particle.
In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structure larger than galaxy-sized as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe. Among the observed phenomena consistent with dark matter observations are the rotational speeds of galaxies and orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
Dark matter also plays a central role in structure formation and galaxy evolution, and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation: the remainder is called the "dark matter component".
The race for the first direct detection of dark matter will move into a new phase in the upcoming months as the ZEPLIN-II instrument is joined by ZEPLIN-III, the world's most sensitive dark matter detector.
Presenting the first results, Dr Alexander Murphy said: "ZEPLIN-II is beginning its second search for dark matter particles, deep underground in a salt and potash mine in North Yorkshire, and we have been pouring through the first data looking for possible interactions with dark matter. Now, just last week, we've had the go-ahead to start operating our next generation detector, ZEPLIN-III. We will be tweaking both detectors to improve their sensitivity all the time and, over the next few months, we'll be able to see signals that are many times fainter. This will give us a fantastic chance of making the first direct detection of a dark matter particle."
Theory suggests that, from time to time, a dark matter particle will scatter from the xenon leaving a very small signal behind. The ZEPLIN-II instrument holds 31 kg of liquid xenon, cooled to a temperature of -110 degrees Celsius and will use extremely sensitive light detectors to view the xenon looking for such a telltale sign.
Although dark matter was detected in space by its gravitational lensing in August 2006, direct observation of these dark matter particles has never yet been made, but the instrument is hoped to catch a glimpse of these exotic particles, so far only theorized.