An Irish physicist has moved to Nevada to do experiments that could help our understanding of deep space. Dick Ahlstrom reports
The light travelling towards us from bright objects in deep space has a tough job getting here. It can get bent by black holes, scrambled by ionised matter and blocked by dust, all factors that make it difficult for astronomers to understand what the light reaching us actually means.
A scientist from Bangor, in Co Down, has joined researchers in Reno, Nevada, to try to understand how at least one of these "confounders" can affect light signals from space. It is a relatively new research area that depends on very advanced equipment, says Dr Shane Scully, a postdoctoral research fellow at the University of Nevada and graduate of Queen's University in Belfast.
The collaboration involves Nevada, the Lawrence Berkeley National Laboratory at the University of California, Justus Liebig University in Germany and the National Autonomous University of Mexico. The focus of the research is the Advanced Light Source at Berkeley, a tremendously powerful facility that can be used to study how light behaves when it interacts with matter.
The team is particularly interested in how light and ionised plasma interact. Plasma is the fourth state of matter, after solid, liquid and gas. Atoms in a plasma have been stripped of one or more of their surrounding electrons, producing a cloud of loose electrons and the altered atoms, known as ions. "The plasma is important because 99 per cent of the universe is in this plasma state," says Scully. By extension, how light and these plasmas interact has a powerful bearing on how we interpret deep-space objects. "All the information we get from deep space as light comes to us through these plasmas. The ions in an interstellar cloud interfere with the photons coming from a star."
The light source becomes very valuable for studying the dynamic between the ions in plasmas and the photons in a beam of light. Quite different from a 100-watt bulb or even a laser, it is a very specialised form of light produced using a cyclotron, a ring-shaped device that uses magnets to trap and accelerate electrons and other atomic particles to velocities approaching the speed of light. The cyclotron accelerates electrons around a storage ring, then uses magnetic fields to make the electrons wiggle. The electrons react by emitting a beam of light photons.
"Its great advantage is it is very bright," says Scully. "Brightness depends on how many photons are in it." The light source can deliver a million million photons per second, making it exceedingly bright.
Another big plus is that the light can be "tuned". The source gives light beyond the wavelengths our eyes can detect, ranging from ultraviolet to "soft" X-ray frequencies.
This makes the cyclotron light very valuable for the team's ion- collision experiments. They can use a variety of photon energies to create the many types of interaction predicted to occur in deep space They can "tickle the outside or smash through the centre of an ion", says Scully. "The photon is exploding the ion, and we are rummaging around to see what happened."
Despite the high light "densities" produced by the source, it is still a challenge to get a photon to strike an ion and, then, measure what happened. There is a lot of space between the ions in a plasma, so most photons pass straight through.
"We are firing a machine gun, the photon beam, at something that isn't there," he says. A punter would have a better chance of success playing the slot machines at the casinos in Reno than hoping for a collision.
Even so, collisions do occur, and magnetic fields are used to capture disintegrated ions and push them along to detectors. The researchers can look at the changed states and study energy peaks after collisions.
All this work using tiny atomic particles adds to our understanding of how the universe's largest objects form, says Scully. It can help predict the elements in interstellar plasma. "That can be very important for how astronomers understand how stars or nebulae form."