Plasma 'fireballs' can now be generated in the laboratory
Researchers at the Institute of Plasmas and Nuclear Fusion (IPFN) are part of an international team of scientists who have developed a new method to experimentally produce plasma of matter-antimatter found in deep space, opening a new frontier in laboratory astrophysics.
Black holes and neutron stars are among the most dense and energetic objects known in the Universe. In these extreme astrophysical environments, there exist plasmas, the fourth fundamental state of matter, alongside solids, liquids, and gases.
Specifically, plasmas under these extreme conditions are known as relativistic electron-positron pair plasmas or 'plasma fireballs' because they consist of electrons and positrons – all moving almost at the speed of light. Although these plasmas are pervasive in deep space conditions, their production in the laboratory has proven to be a challenge.
Now, for the first time, an international team of scientists, including researchers from the IPFN /Instituto Superior Técnico, has experimentally generated high-density relativistic electron-positron pair plasma beams, producing two to three orders of magnitude more pairs than previously reported. The team's results were published in the journal Nature Communications. This discovery opens the door to experiments that could lead to fundamental discoveries about the workings of the Universe.
'The generation of laboratory-produced plasma fireballs composed of matter-antimatter and photons is a research goal at the forefront of high-energy density science,' explains lead author Charles Arrowsmith, a physicist at the University of Oxford. 'But until now, the experimental difficulty of producing electron-positron pairs in sufficient numbers has limited our understanding to purely theoretical studies,' he adds.
Luís Oliveira e Silva, a professor in the Department of Physics at Instituto Superior Técnico and Coordinator of the Lasers and Plasmas Group/IPFN, along with PhD students Pablo Bilbao and Filipe Cruz, collaborated with Arrowsmith and other scientists in designing an innovative experiment that uses the HiRadMat facilities at the Super Proton Synchrotron (SPS) accelerator of the European Organization for Nuclear Research (CERN) in Geneva, Switzerland.
This experiment generated extremely high, almost neutral electron-positron beams using more than 100 billion protons from the SPS accelerator. Each proton carries a kinetic energy that is 440 times greater than its rest energy. Due to this high momentum, when the proton smashes into an atom, it has enough energy to release its internal constituents – quarks and gluons – which immediately recombine to produce a shower of elementary particles. In other words, the beam generated in the laboratory had enough particles to start behaving like an astrophysical plasma.
'This opens an entirely new frontier in laboratory astrophysics, making it possible to experimentally probe the microphysics of gamma-ray bursts or blazar jets,' says Arrowsmith.
The team also developed techniques to modify the pair beam emissions, making it possible to conduct controlled studies of plasma interactions on scales similar to those of astrophysical systems. 'Space and ground-based telescopes are not capable of seeing the smallest details of these distant objects, and until now, we could only rely on numerical simulations. Our laboratory work will allow us to test predictions obtained from very sophisticated calculations and validate how cosmic fireballs are affected by the tenuous interstellar plasma,' says co-author Gianluca Gregori, a professor of physics at the University of Oxford.
Additionally, he adds, 'this achievement highlights the importance of exchange and collaboration between experimental facilities worldwide, especially as they open new pathways in accessing increasingly extreme physical regimes.'
Apart from Instituto Superior Técnico, the University of Oxford, and CERN, the institutions that collaborated in this research include the University of Rochester, the Science and Technology Facilities Council Rutherford Appleton Laboratory (STFC RAL), the Atomic Weapons Establishment in the UK, the Lawrence Livermore National Laboratory, the Max Planck Institute in Germany, and the University of Iceland.
Full article:
https://www.nature.com/articles/s41467-024-49346-2
