Utilizzo dell’orbita lunare come potente rivelatore di nuove onde gravitazionali

I ricercatori dell’UAB, dell’IFAE e dell’University College di Londra propongono di utilizzare le variazioni di distanza tra la Terra e la Luna, che possono essere misurate con una precisione inferiore a un centimetro, come un nuovo rivelatore di onde gravitazionali all’interno di una gamma di frequenze che i dispositivi attuali non può rilevare. La ricerca, che potrebbe aprire la strada al rilevamento di segnali dall’universo primordiale, è stata pubblicata di recente in Lettere di revisione fisica.

Le onde gravitazionali, previste da Albert Einstein all’inizio del 20° secolo e rilevate per la prima volta nel 2015, sono i nuovi messaggeri dei processi più violenti in atto nell’universo. I rilevatori di onde gravitazionali scansionano diverse gamme di frequenza, in modo simile allo spostamento di un quadrante quando ci si sintonizza su una stazione radio. Tuttavia, ci sono frequenze impossibili da coprire con i dispositivi attuali e che possono ospitare segnali fondamentali per la comprensione del cosmo. Un esempio particolare può essere visto nelle onde microhertz, che potrebbero essere state prodotte all’alba del nostro universo e sono praticamente invisibili anche alla tecnologia più avanzata oggi disponibile.

In un articolo recentemente pubblicato sulla prestigiosa rivista Lettere di revisione fisica, Diego Blas del Dipartimento di Fisica dell’Universitat Autònoma de Barcelona (UAB) e dell’Institut de Física d’Altes Energies (IFAE), e Alexander Jenkins dell’University College London (UCL), sottolineano che un rilevatore di onde gravitazionali naturali esiste nel nostro ambiente immediato: il Sistema Terra-Luna. il[{” attribute=””>gravitational waves constantly hitting this system generate tiny deviations in the Moon’s orbit. Although these deviations are minute, Blas and Jenkins plan on taking advantage of the fact that the Moon’s exact position is known with an error of at most one centimeter, thanks to the use of lasers sent from different observatories which are continuously reflected upon mirrors left on the surface of the Moon by the Apollo space mission and others. This incredible precision, with an error of one billionth of a part at most, is what may allow a small disturbance caused by ancient gravitational waves to be detected. The Moon’s orbit lasts approximately 28 days, which translates into a particularly relevant sensitivity when it comes to microhertz, the frequency range researchers are interested in.

Similarly, they also propose using the information other binary systems in the universe may provide as gravitational wave detectors. This is the case of pulsar binary systems distributed throughout the galaxy, systems in which the pulsar’s radiation beam allows obtaining the orbit of these stars with incredible precision (with a precision of one millionth). Given that these orbits last approximately 20 days, the passing of gravitational waves in the microhertz frequency range affect them particularly. Blas and Jenkins concluded that these systems could also be potential detectors of these types of gravitational waves.

With these “natural detectors” in the microhertz frequency range, Blas and Jenkins were able to propose a new form of studying gravitational waves emitted by the distant universe. Specifically, those produced by the possible presence of transitions in highly energetic phases of the early universe, commonly seen in many models.

“What is most interesting perhaps is that this method complements future ESA/NASA missions, such as LISA, and observatories participating in the Square Kilometer Array (SKA) project, to reach an almost total coverage of the gravitational waves from the nanohertz (SKA) to the centihertz (LIGO/VIRGO) frequency ranges. This coverage is vital to obtaining a precise image of the evolution of the universe, as well as its composition”, Diego Blas explains. “Covering the microhertz frequency range is a challenge, which now may be feasible without the need of building new detectors, and only observing the orbits of systems we already know. This connection between fundamental aspects of the universe and more mundane objects is particularly fascinating and can eventually lead to the detection of the earliest signals we have ever seen, and thus change what we know about the cosmos”, he concludes.

Reference: “Bridging the μHz Gap in the Gravitational-Wave Landscape with Binary Resonances” by Diego Blas and Alexander C. Jenkins, 11 March 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.128.101103

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