Supernova-creating particle accelerators will make the biggest bangs we have ever known
Two new experimental facilities, billed as the successors to the Large Hadron Collider, will recreate the supernova explosions that produced all matter. Richard Gray reports
Every inch of your body – as well as the newspaper you are reading, the chair you are sitting on and the entire world around you – is made up of a combination of fewer than 100 basic chemical building blocks. These will be familiar to every student who has seen the periodic table hanging on a classroom wall: they are the elements, the various atoms that make up the universe around us.
The periodic table is meant to be an authoritative list, but scientists believe there are a few elements missing. Well, not exactly a few – more likely between 3,500 and 7,000. And now they are preparing to build a series of giant new machines to find them. This new breed of atom-smashers, billed as the successors to the Large Hadron Collider (LHC) at Cern in Geneva, will recreate some of the most extreme conditions found in the universe, creating miniature supernovae (huge explosions triggered when stars collapse), neutron stars and even the mysterious vampire stars right here on planet Earth.
Inside the replicas of these cataclysmic cosmic explosions, scientists expect to find atoms that have never been seen before winking in and out of existence. It is a search for what nuclear physicists describe as terra incognita, an unknown land of atomic science.
"Nobody knows exactly how many elements are out there waiting to be discovered," explains Professor Guenther Rosner, a physicist at Glasgow University who sits on the committee at the European Science Foundation that has just published the long-term plan for a new generation of giant experimental facilities. "The estimate is that there are at least another 4,000 or 5,000. They are thought to be generated in supernova explosions, so we are sure they are out there. Unfortunately, these atoms are also going to be extremely short-lived, lasting just a trillionth of a trillionth of a second before disappearing.
While the 16-mile LHC has been searching for the elusive subatomic particles that make up atoms and give them mass, these new experiments will aim to answer fundamental questions about atoms themselves by revealing how they are created.After the Big Bang, just a handful of elements were brought into existence, namely the lightest and simplest atoms like hydrogen and helium. It was not until these were subjected to the furnaces of the first stars and the massive heat of supernovae, which explode with temperatures in excess of 180 billion degrees Fahrenheit (100 billion Kelvin), that larger atoms began to emerge.
Under the plans set out by the European Science Foundation's Nuclear Physics Collaboration Committee, two "next-generation" super-accelerators have now been approved to reproduce these extreme conditions.
The first, the Facility for Antiproton and Ion Research (Fair), which is to be sited in Darmstadt in Germany, will accelerate atoms inside a double ring with a circumference of more than 3,000 feet before smashing them into a fixed target that causes them to fragment. The fragments will then be accelerated and smashed into a second target to produce temperatures more than a million times hotter than the centre of the Sun. Scientists say the intense and dense explosions generated will produce conditions thought to exist inside neutron stars – the remnants of massive stars that have collapsed under their own gravity during an supernova explosion.
"Fair will generate matter that is about 10 times denser than is possible at the LHC, so that it resembles the matter at the centre of neutron stars," says Prof Rosner. "We don't know what the interior of a neutron star is, but it is probably not normal matter – it will be strange and very exciting."
The £1 billion facility will also be able to produce beams of antimatter that can be collided with ordinary matter to produce entirely new types of particles. Among the exotic objects they will be looking for are bizarre balls of energy that behave like particles known as "glueballs". These hypothetical particles are made up of gluons, one of the elementary particles thought to hold the nucleus of atoms together.
"We will be able to address a very broad spectrum of science that will answer some really fundamental questions," explains Professor Martin Freer, a nuclear physicist at Birmingham University who is involved in one of the experiments at Fair. "Things like how atoms first formed, what happens to terra incognita elements and what sits at the heart of neutron stars that we have only been able to see at the centre of echoes left behind by supernova explosions."
The second of the advanced facilities to be given approval is the European Isotope Separation On-Line facility, or Eurisol, which will smash atoms into a thick target; the fragments will be
re-accelerated to produce intense beams that can be smashed into another target.
"The advantage of this approach is that all the power is absorbed by the target, which can produce the heavy, unstable atoms that are synthesised by supernova explosions," says Dr Yorick Blumenfeld of the Institut de Physique Nucléaire in France, the project leader for Eurisol. "One could extrapolate the properties of these elements and so understand neutron stars and how they behave."
Among the sites being considered for Eurisol, which is currently scheduled for completion in 2025, are the Rutherford Laboratories in Oxford, although it could also be sited at Cern alongside the LHC.
When complete, it could allow some of the most exotic and destructive forces in the universe to be replicated. Some of the strangest are "vampire stars", objects that suck gas from stellar neighbours which is thought to ignite exotic nuclear reactions that create unusual types of atoms.
It is hoped that studying these processes will not only reveal new insights into the universe, but also provide new ways of generating energy and cleaning up nuclear fuel, as well as providing diagnostic and therapeutic tools for medicine, and even generating new materials from exotic matter.
For scientists such as Prof Rosner, the ultimate prize will be unravelling why we are here in the first place. "We owe our existence to supernovae and other events deep in outer space," he says. "All of the heavy atoms and radioactive atoms we rely upon, like uranium, were created in these processes. Life would not exist if they had not been created.
"Radioactive decay generates a large fraction of the heat that keeps the surface of the Earth from freezing over, so understanding how these atoms were created could give us the ultimate answer to how we came to be here."