ESPRESSO spectrograph tests fundamental constant of physics

In an attempt to answer the apparently simple and colloquial question "are the laws of physics the same in all parts of the universe, and at all times?", an international team of researchers, which includes the participation of Portuguese researchers from the Institute of Astrophysics and Space Sciences (IAstro), has carried out the CosmoESPRESSO project, which aims to find out whether the alpha constant (α) - the so-called fine structure constant, considered one of the fundamental constants of physics and which corresponds, briefly, to the strength of the electromagnetic interaction between particles - undergoes variations in time and space, i.e. whether it is, in fact, constant.

Carlos Martins, from IAstro, said in a statement that "astronomers have made hundreds of measurements of alpha over the last two decades, some of which seemed to say that alpha varied over billions of years, and also with spatial location". Based on the hypothesis that these variations could be the result of problems in the measuring instruments, the team designed a spectrograph - ESPRESSO - which, in conjunction with the VLT (Very Large Telescope), constitutes a "perfect machine for measuring alpha", in the words of Paolo Molaro, coordinator of the research project. With this equipment, they were able to take measurements of the alpha constant with unprecedented accuracy, by observing the light of a quasar - an extremely luminous object, detectable from Earth, but very distant.

The results of the research, which have now been published in the form of an article in the journal Astronomy & Astrophysics, show variations of around 1.3 parts per million, significantly less than the 10 parts per million of some previous measurements. The team thus demonstrates that the accuracy of the measurements depends on the amount of light that can be collected with the measuring instruments used. The higher resolution of the VLT and ESPRESSO allows a greater approximation to the real value of alpha, and the new generations of telescopes and spectrographs, already under development, will lead to even more accurate results.

The project to design and build ESPRESSO involved several European research units. In Portugal, the Institute of Astrophysics and Space Sciences participated, with funding from FCT. In addition to measuring physical constants, the spectrograph is also used, famously, in the search for Earth-like planets located in the habitable zone of distant stars.