The extraordinary seismic silence makes the Nuoro site particularly suitable for hosting the gravitational wave observatory designed for the study of the universe
In order to create a third generation gravitational wave observatory, the Einstein Telescope - ET, capable of observing cosmic processes with sensitivity never before achieved, a multidisciplinary team, led by researchers from the National Institute of Geophysics and Volcanology ( INGV), the National Institute of Nuclear Physics (INFN) and the University of Sassari, conducted a study on the now abandoned metal mine of Sos Enattos in Sardinia, thanks to the support of IGEA SpA, the company that now manages it . Sos Enattos, which is immersed in a landscape of rare beauty in the province of Nuoro a short distance from Monte Albo, declared a "site of community interest" (SIC) by the European Union, is, in fact, the Italian site candidate to host the new observatory.
The multidisciplinary study, in which researchers from INGV, INFN, the Universities of Sassari, Padua, Sapienza of Rome, "Federico II" of Naples, the Gran Sasso Science Institute (GSSI) and the European Gravitational Observatory of Pisa, which had the objective of seismologically characterizing the Sos Enattos site, has demonstrated its full suitability for hosting ETs.
The results of the study “A Seismological Study of the Sos Enattos Area - the Sardinia Candidate Site for the Einstein Telescope” have just been published in the international journal Seismological Research Letters.
Einstein Telescope (ET) will be a highly sensitive instrument that will make a decisive contribution to improving our knowledge of the universe and the physical processes that govern it. For this reason it will be able to play a key role worldwide in research activity in the field of gravitational waves, from both a scientific and an infrastructural point of view.
Therefore it is considered a strategic project by the European scientific community and is supported by various countries including Italy which last September, through the Ministry of University and Research, nominated it for the next ESFRI Roadmap 2021 European Strategy Forum on Research Infrastructure, the strategic European forum that identifies which will be the future major research infrastructures in which to invest at European level.
To operate to the best of its potential, the ET observatory will have to be built in a geologically stable and sparsely inhabited area: ground vibrations (of both artificial and natural origin) can, in fact, mask the weak signal generated by the passage of a gravitational wave. There are two candidate sites to host it: Sardinia with Sos Enattos, in fact, and Limburg - a region on the border between Belgium, Germany and the Netherlands.
“To characterize a site seismologically”, explains Carlo Giunchi, INGV researcher “it means identifying the background noise caused by natural vibrations and human activity. We have therefore installed, in collaboration with the INFN and the University of Sassari, some seismometers at the Sos Enattos mine to analyze, down to the minimum values, the amplitude and frequency of the vibrations and understand their main sources. From the recordings made it emerged that we are in one of the quietest sites in the world, a feature that makes it particularly suitable for the installation of the ET telescope since only in these conditions does it maximize its ability to detect cosmic events. Furthermore, one of the sensors installed has become part of the INGV National Seismic Network, which is thus enriched with a high-quality measurement station".
“The study of gravitational waves”, continues Luca Naticchioni, INFN researcher, “it is very important because it allows us to shed light on cosmic phenomena such as the merger of binary systems of black holes and neutron stars, providing valuable information, both for fundamental physics and for the study of the evolution of the universe. These phenomena, which occur at enormous distances, cause perturbations in the "fabric" of spacetime which can be observed from the ground using laser interferometry with extremely sensitive and complex detectors. The study of the Sos Enattos site, candidate to host ET, involved bodies with different disciplinary characteristics but with interesting complementarities, such as INFN and INGV”.
“The Next Step”, adds Domenico D'Urso of the University of Sassari, “will be to characterize the subsoil of the site in question because the large gravitational wave detector will consist of a system of underground tunnels arranged in a triangular arrangement which will host very high precision laser interferometers. These surveys will be necessary to understand how to fine-tune the tunnel system, while identifying the sources of noise and minimizing its effects".
“We expect finally”, concludes Gilberto Saccorotti of INGV, “the installation of a large number of seismometers which, functioning as an antenna, will make it possible to measure the directions of propagation of the elastic waves which constitute the seismic noise, in order to better understand the phenomena which generate it. The collaboration put in place for this study has produced an exceptional synergy between the various research institutions and universities, providing solid foundations for a wide-ranging and long-term project such as ET, and offering, among other things, results that can be used immediately for seismic monitoring constantly implemented by INGV throughout the national territory”.
Link to the article: https://doi.org/10.1785/0220200186
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From the Mine to Gravitational Waves: Sos Enattos in Sardinia identified as the ideal site for the ET observatory
The extraordinary seismic silence makes the Nuoro site particularly suitable for hosting the gravitational wave observatory designed for the study of the universe
In order to implement a third - generation gravitational wave observatory, the Einstein Telescope – ET, able to observe cosmic processes with unprecedented sensitivity, a multidisciplinary team led by researchers from the National Institute of Geophysics and Volcanology (INGV), the National Institute of Nuclear Physics (INFN) and the University of Sassari conducted a study on the dismissed metal mine of Sos Enattos, in Sardinia, thanks to the support of IGEA SpA, the company that now manages the mine. Sos Enattos which is surrounded by a landscape of rare beauty in the province of Nuoro, is also close to Monte Albo, declared a site of community interest by the European Union (SIC). The site is now the Italian candidate to host the new observatory.
The multidisciplinary study, in which researchers from INGV, INFN, the Universities of Sassari, Padua, Sapienza of Rome, "Federico II" of Naples, the Gran Sasso Science Institute (GSSI) and the European Gravitational Observatory of Pisa participated, had the aim of seismologically characterizing the Sos Enattos site. It has demonstrated its full suitability to host ET. The results of the study"A Seismological Study of the Sos Enattos Area - the Sardinia Candidate Site for the Einstein Telescope” have just been published in the international journal Seismological Research Letters.
Einstein Telescope (ET) will be a highly sensitive instrument that will contribute decisively to improve our knowledge of the universe and the physical processes that govern it. For this, it will be able to play a key role worldwide in research in the field of gravitational waves, from both a scientific and infrastructural point of view.
Therefore, it is considered a strategic project by the European scientific community, and is supported by several countries including Italy, which last September, through the Ministry of University and Research, nominated it for the next ESFRI European Strategy Roadmap 2021 Forum on Research Infrastructure, the European strategic forum that identifies the future major research infrastructures in which to invest at European level.
To operate at its best, the ET observatory requires a geologically stable and sparsely inhabited area; the vibrations of the ground (of either artificial or natural origin) can in fact mask the weak signals generated by the passage of a gravitational wave. Sardinia and Limburg – a region at the borders between Belgium, Germany and Holland - are the candidate sites to host it.
"The seismological characterization of a site”, explains Carlo Giunchi, researcher at INGV, "means measuring the background vibrations of the soil caused by natural sources and anthropogenic activity. We have therefore installed, in collaboration with INFN and the University of Sassari, some seismometers at the Sos Enattos mine to analyse, down to the minimum values, the amplitude and frequency of vibrations and understand their main sources. From the recordings, it emerged that we are dealing with one of the quietest sites in the world, a feature that makes it particularly suitable for the installation of the ET telescope which only in such conditions maximizes its capabilities for detecting cosmic events. In addition, one of the sensors installed has become part of the INGV National Seismic Network, which is thus enriched with a high-quality measurement station".
“The study of gravitational waves”, continues Luca Naticchioni, INFN researcher, “is very important because it allows to shed light on cosmic phenomena such as the fusion of binary systems of black holes and neutron stars, providing valuable information for fundamental physics and for the study of the evolution of the universe. These phenomena, which occur at enormous distances, cause perturbations in the “fabric” of spacetime that can be observed from Earth by laser interferometry with extremely sensitive and complex detectors. The study of the Sos Enattos site, a candidate to host ET, involved entities with different disciplinary characterizations, such as INFN and INGV, but with interesting complementarity”.
“The next step”, adds Domenico D'Urso of the University of Sassari, “will be to characterize the subsoil of the site in question because the large gravitational wave detector will consist of a system of underground tunnels arranged in a triangular shape that will host very high precision laser interferometers. These measurements will be necessary to understand how to fine-tune the tunnel system, while identifying the sources of the noise and minimizing the related effects”.
“Finally”, concludes Gilberto Saccorotti of INGV, “we foresee the installation of a large number of seismometers which, functioning as an antenna, will allow to measure the propagation directions of the elastic waves that compose the seismic noise, thus allowing an improved understanding of its causative phenomena. The collaboration established for this study has produced an exceptional synergy between the various Research Bodies and Universities, providing solid foundations for a wide-ranging and long-term project such as ET, and offering results of immediate use for the seismic monitoring, constantly implemented by INGV throughout the national territory".
Link to the article: https://doi.org/10.1785/0220200186
Fig. 1 - Rendering of the Einstein Telescope. The underground infrastructure, with 10km long tunnels, will host 6 interferometers dedicated to the observation of gravitational waves
Fig 1 - Artistic rendering of the Einstein Telescope. The underground infrastructure, with10km-long tunnels, will host 6 interferometers for the observation of Gravitational Waves
Fig 2 - Probability distribution of the spectral power of the seismic noise for a station located at a depth of 84 meters, in one of the tunnels of the Sos Enattos mine. The colors indicate the probability of observing a given seismic signal strength, as a function of frequency. The gray lines correspond to the upper and lower seismic noise patterns
Fig 2 - Probabilistic Power Spectral Densities for a station located at a depth of 84 meters below the surface, within a tunnel of Sos Enattos' mine. Colors indicate the probability of observing a given spectral power, as a function of frequency. Gray lines correspond to the Low- and High-Noise Earth models. The blue line is the sensitivity bound of the seismometer.