CERN Courier December 2017 CERN Courier December 2017 Sciencewatch Astrowatch

C o m p i l e d b y J o h n S w a i n , n ortheaStern U n i v e r S i t y C o m p i l e d b y m e r l i n K o l e , d e pa r t m e n t o f pa r t i C l e p h y s i C s , U n i v e r s i t y o f G e n e va Superfluidity at room temperature Extreme cosmic rays reveal clues to origin

The energy spectrum of cosmic rays 90 A sky map in equatorial continuously bombarding the Earth spans 0.46 co-ordinates showing the Superfluidity, like superconductivity, is Interference fringes in a polariton many orders of magnitude, with the highest cosmic-ray flux above typically thought of as needing very low condensate as it transitions to a fluid with energy events topping 108 TeV. Where these km 8 EeV, revealing a clear –2

temperatures that alter the fundamental zero viscosity, from simulations. extreme particles come from, however, has sr dipole structure with a quantum-mechanical behaviour of materials. remained a mystery since their discovery 360 0 0.42 –1 significance of 5. 2σ. The yr Pierre Auger Collaboration

Surprisingly, Giovanni Lerario of CNR thin amorphous layer of fluorescent organic more than 50 years ago. Now the Pierre Auger –1 galactic centre is marked NANOTEC Institute of Nanotechnology in material between them. A laser pulse collaboration has published results showing with an asterisk and the Italy and colleagues now report what appears creates a polariton flow with well-defined that the arrival direction of ultra-high-energy galactic plane is shown by to be superfluidity at room temperature. The energy, revealing itself as a superfluid by 0.38 cosmic rays (UHECRs) is far from uniform, –90 a dashed line. “material” in question is a highly exotic state the disappearance of scattering around giving a clue to their origins. of bosonic quasiparticles called a polariton an obstacle. The discovery in 1963 at the Vulcano detectors spread over an area of 3000 km2 the sky known to have a large density of condensate, and the experiment comprised Ranch Experiment of cosmic rays with near the town of Malargüe in western galaxies, supporting the view that UHECRs an optical Fabry–Pérot microcavity made ● Further reading energies exceeding one million times the Argentina. Like the first cosmic-ray are produced in other galaxies. The lack of from two dielectric Bragg mirrors with a G Lerario et al. 2017 Nature Physics 13 825. energy of the protons in the LHC raised detectors in the 1960s, the array measures anisotropy at lower energies could be a result many questions. Not only is the charge the air showers induced as the cosmic rays of the higher deflection of these particles in Spiders and graphene Molecular assembler of these hadronic particles unknown, but interact with the atmosphere. The arrival the galactic magnetic field. Dog voting by sneeze the acceleration mechanisms required to times of the particles, measured with GPS The presented dipole measurement is based Spider silk famously has excellent mechanical Nano machines that could put together produce UHECRs and the environments receivers, are used to determine the direction on a total of 30,000 cosmic rays measured properties, having both high strength (around African wild dogs, Lycaon pictus, a highly social molecules mechanically one by one, also that can host these mechanisms are still from which the primary particles came by the Pierre Auger Observatory, which is 1.5 GPa) and toughness (around 150 J/g). and co-operative species, vote called molecular assemblers, typically being debated. Proposed origins include within approximately one degree. currently being upgraded. Although the Nicola Maria Pugno of the University of by sneezing, according to findings by Reena have been the stuff of futurists. Now, Salma sources in the galactic centre, extreme The collaboration studied the arrival results indicate an extragalactic origin, the Trento and colleagues have now found a Walker of the Botswana Predator Conservation Kassem and colleagues at the University of supernova events, mergers of neutron stars, direction of particles with energies in particular source responsible for accelerating way to dramatically improve on these by Trust and Brown University in Providence and Manchester in the UK have demonstrated an and extragalactic sources such as blazars. the range 4–8 EeV and for particles with these particles remains unknown. The feeding spiders aqueous dispersions of colleagues. The team reports that when the actual example. The assembler is a single large Unlike the case with photons or neutrinos, energies exceeding 8 EeV. In the former upgraded observatory will enable more data graphene or carbon nanotubes, which are then dogs meet in social rallies before collective molecule that can be switched via pH between the arrival direction of charged cosmic rays data set, no clear anisotropy was observed, to be acquired and allow a more detailed incorporated into their silk. Fracture strength motions, the probability of the success of a left- and right-handed mode. It can assemble does not point directly towards their origin whereas for particles with energies above investigation of the currently studied energy went up to around 5.4 GPa and the toughness rally is determined by the number of sneezes in four stereoisomers of a molecule depending because, despite their extreme energies, 8 EeV a dipole structure was observed (see ranges. It will also open the possibility to modulus to 1570 J/g. This is just a first step and the rally. The quorum was reduced if dominant on the order in which switches in handedness their paths are deflected by magnetic fields figure), indicating that more particles come explore even higher energies where the opens the door to a new class of artificially individuals initiated the rally, but such are made, making such machines promising both inside and outside our galaxy. Since from a particular part of the sky. Since magnetic-field deflections become even modified biological material, says the team. dominant individuals could also be “overruled” for future chemical synthesis and molecular the deflection reduces as the energy goes up, the maximum of the dipole is outside the smaller, making it possible to study the origin of UHECRs, their acceleration mechanism by a consensus of enough subordinates. manufacturing. however, some UHECRs with the highest galactic plane, the measured anisotropy is ● Further reading energies might still contain information consistent with an extragalactic nature. The and the magnetic fields that deflect them. about their arrival direction. collaboration reports that the maximum, E Lepore et al. 2017 2D Materials 4 031013. ● Further reading ● Further reading ● Further reading R Walker et al. 2017 Proc. Roy. Soc. B S Kassem et al. 2017 Nature 549 374. At the Pierre Auger Observatory, cosmic when taking into account the deflection of rays are detected using a vast array of magnetic fields, is consistent with a region in Pierre Auger Collaboration 2017 Science 357 1266. Self-interacting dark matter DOI: 10.1098/rspb.2017.0347. 3D metal printing In explaining the diversity of rotation Picture of the month curves measured for spiral galaxies, the Researchers have taken an important step simplest cold-dark-matter (CDM) models towards 3D printing of high-strength metals. This image might appear to show a large empty patch in the sky run into difficulties. It appears, however, Despite the huge growth of 3D printing without any stars, but in reality it shows a molecular cloud in our galaxy that self-interacting dark matter (SIDM) in recent years, the way metal grains obscuring our view. A high concentration of dust and molecular gas does better. Ayuki Kamada of the University are printed and incorporated can lead to absorbs almost all of the visible light emitted from the stars behind it, of California at Riverside and colleagues microstructures with large columnar grains producing the black patch. The molecular cloud shown in this image is assume only the halo concentration-mass and periodic cracks. John Martin of HRL known as Barnard 68, which is relatively nearby at about 500 light-years FORS Team/8.2m VLT Antu/ESO relation predicted by CDM and a fixed Laboratories and the University of California away and is half a light-year across. Molecular clouds are almost value for the self-interaction cross-section. and colleagues have shown that adding impenetrable for radiation in the visible part of the spectrum, but Although the specific nature or composition nanoparticles to the metallic powders used the stars behind them can be observed in the infrared. Furthermore, of the dark matter required still remains a as the “printer ink” results in crack-free and observations of these objects at submillimetre wavelengths can show puzzle, the team shows that the impact of regularly grained printed materials with stars forming in molecular clouds (CERN Courier September 2017 p15). baryons on the SIDM halo profile and the strengths comparable to wrought materials. The stars form as dense regions of the cloud collapse into themselves to scatter from the assembly history of halos More than 5500 alloys in use today could form areas dense enough to initiate the burning of hydrogen. can explain the diverse rotation curves. Specific behavioural mechanisms such as potentially benefit from the technique. sneezing may shape decision-making in a ● Further reading wild, socially complex animal society. ● Further reading A Kamada et al. 2017 Phys. Rev. Lett. 119 111102. J Martin et al. 2017 Nature 549 365.

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