The Physics World top 2017 Breakthrough of the Year awarded by the prestigious magazine Physics World has gone to the international team of astronomers and astrophysics that made the first ever multi-messenger observation involving gravitational waves and electromagnetic radiation from the merger of two neutron stars in a binary system in the galaxy NGC 4993 located about 130 million light-years from Earth. The Pierre Auger Collaboration contributed to this effort by searching for ultra-high energy neutrino emission from this remarkable source (Astrophysical Journal Letters 848 (2017) no.2, L12; Astrophysical Journal Letters 850 (2017) no. 2, L 35). The latter publication illustrates the outstanding directional sensitivity of the Observatory for Earth Skimming Neutrinos. In addition, the Auger Collaboration has been awarded one of the Physics World top 10 breakthroughs of 2017, for the recent unveiling of the 50 year-old mystery about the origin of the highest energy cosmic rays, subatomic particles with energies about millions of times greater than the protons accelerated in the Large Hadron Collider. By studying the distribution of the arrival directions of more than 30,000 cosmic particles, the Pierre Auger Collaboration discovered that the ultra-high-energy cosmic rays have an extragalactic origin (Science 357, 1266-1270 (2017)).
The Astroparticle Physics group at IGFAE led by Prof. Enrique Zas contributed directly to these two breakthroughs. In the 90’s the group proposed to use the Surface Detector of the Auger Observatory to search for ultra-high energy neutrinos. Since then many members of the group have been leading this effort. “In this new era of the Multi-messenger Astronomy, exciting years await us in Astrophysics, Astronomy and Physics and the Pierre Auger Collaboration will keep contributing to this worldwide collaborative effort” says Jaime Alvarez-Muñiz who coordinates the search for neutrinos in Auger. The Astroparticle Physics group at IGFAE has also played a fundamental role in the second breakthrough achieved by the Auger Collaboration. By analysing inclined showers induced by ultra-high energy cosmic rays that arrive at Earth at large angles with respect to the vertical to the ground, the field of view of the Auger Observatory was extended towards the Northern hemisphere allowing the collaboration to compare the rates of cosmic rays from most directions in the sky and finding a dipolar anisotropy incompatible with a galactic origin. “We are very proud to have contributed to this exciting result that solves one of the open questions in modern Astrophysics. Our next step will be to identify the actual sources of cosmic rays thanks to the data collected with the upgrade of the observatory, the AugerPrime” says Inés Valiño, IGFAE researcher who coordinates the work devoted to the reconstruction and analysis of inclined air showers in Auger and to the measurement of the energy spectrum of ultra-high energy cosmic rays.
The Astroparticle Physics group is composed of five senior members (Jaime Alvarez-Muñiz, Gonzalo Parente, Inés Valiño, Ricardo Vázquez and Enrique Zas) and three young researches (Aida López Casado, Francisco Pedreira and Guillermo Torralba). The group participates in the Pierre Auger Observatory since 2002 when Spain became a full member of the Pierre Auger Collaboration consisting of more than 400 scientists from 20 countries.