ESPRESSO spectrograph tests fundamental constant in physics

In an attempt to answer the seemingly simple and colloquial question "are the laws of physics the same everywhere in the universe, and at all times?", an international team of researchers, including Portuguese researchers from the Institute of Astrophysics and Space Sciences (IAstro), has developed the CosmoESPRESSO project, which aims to investigate whether the alpha constant (α) – the so-called fine structure constant, considered one of the fundamental constants of physics and which corresponds, succinctly, to the strength of the electromagnetic interaction between particles – varies in time and space, that is, whether it is, in fact, constant.

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

The results of the research, which are now published in the form of an article in the journal Astronomy & Astrophysics, report variations in the order of 1.3 parts per million, significantly lower 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 for a closer approximation of the true value of alpha, and the new generations of telescopes and spectrographs, already under development, will lead to even more accurate results.

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