Gravitational waves (GW) are ripples in spacetime that travel at the speed of light. They are predicted in Albert Einstein's theory of General Relativity. On September 14th, 2015 the LIGO Scientific Collaboration and the Virgo Collaboration observed them for the first time, using data from the two LIGO detectors. That first gravitational wave signal is known as GW150914.
The GW project at CIEMAT takes place within the Divisions of Astroparticle Physics, High Energy Particle Physics and Scientific Computing, of the Basic Research Department. The areas of focus of our research group are the measurement of cosmology parameters using the EM spectrum; the study of extreme and exotic objects of the universe using high energy gamma rays and with neutrinos in the future; or the search for dark matter through the production in accelerators, direct detection in underground laboratories, and indirect detection in space detectors and with high energy gamma rays. Our research team has a track of more than 30 years of direct involvement in the development and exploitation of accelerator instrumentation (L3, CMS), particle space instrumentation (AMS-02), dark matter underground instrumentation (DEAP-3600, DarkSide), and very high energy gamma-ray instruments (MAGIC, CTA). An important capability of our group is the expertise in computing for scientific exploitation: our group manages the Port d'Informació Científica (PIC) together with IFAE, a scientific data centre in Barcelona that specialises in data-intensive research and operates production data services for several large experiments such as the LHC, MAGIC and CTA; and we host and manage a Tier-2 data centre for CMS. One of the members of the research team has been directly involved in these projects. Also, the research team has demonstrated experience in Artificial intelligence and has applied it in the data analysis of a variety of particle and astroparticle physics experiments using GPU computing.
The detection of gravitational waves in 2015, announced in 2016 by LIGO, was a major breakthrough in the field of observational fundamental physics. Beyond its intrinsic scientific value, it opened a new messenger to study the universe in ways that were not previously possible and are complementary to methodologies used until now. In particular, we identified the research lines of CIEMAT dealing with Cosmology, the study of extreme objects and the search for dark matter can greatly profit from this new channel, building up a multimessenger approach to these topics.
The gravitational wave interferometers Ligo, Virgo and Kagra are being upgraded to start a new run covering 2023 and 2024 (O4) with enhanced sensibility with respect to previous runs. It is expected that there would be about 1000 new sources detected in one year compared with a total of 100 sources in the previous three runs, representing a shift from the discovery regime to the statistical analysis regime. In addition, a new upgrade is planned to take place for the following 2026 run (O5) with another 10-fold increase in the number of sources detected per year.
Our group is a member of the Virgo collaboration, which has welcomed the expertise of CIEMAT and accepted the contribution in developing hardware to increase the sensibility of the Virgo interferometers for O5; developing and deploying an off-site computing cluster for the low latency pipeline for O4 and O5; and contribute on the detector characterisation in O4.
Regarding our scientific goals during O4 we will focus on: the search for primordial black holes as dark matter candidates, by searching for mergers where one of the members of the pair is a (near spinless) black hole with a mass close to the Chandrasekar limit; the determination of cosmological parameters using gravitational waves, in particular dark sirens, during O4; and the search follow up of extreme event counterparts with very high energy telescopes. In order to contribute efficiently to these topics, we have already started a collaboration with the gravitational waves group of IFT (CSIC-UAM) which is already a member of the Virgo collaboration. With the expected statistics for O4, the outcome in the case of dark matter will be the discovery of a candidate or setting of a stringent limit in the models for the formation of primordial black holes; and together with O5, the expected error in the determination of the Hubble constant will be competitive enough to provide a handle in solving the current tension between the local and cosmological scale determinations.
We also participate in the Einstein Telescope, planned to be operative in the early 2030s. This next-generation gravitational-wave detector has recently been designated as a European Strategy Forum on Research Infrastructures facility, highlighting its importance in the scientific community, and has started its Preparatory-Phase. Our main contributions to the project will be in the design of the computing model together with PIC, as well as the design of mechanical elements for the interferometer, drawing on our experience from our previous participation in the Virgo project. Additionally, we will work closely with CIEMAT's Technology Department to prepare for production, and we will start developing the next generation of scientists who will be involved in the project.