Einstein telescope, so we will study the “dark age” of the Universe

It will be the largest gravitational wave detector ever built and will serve to push us to study the universe before the formation of stars

(Image: Einstein Telescope)

It European strategy forum on research infrastructures (ESFRI), the agency responsible for indicating scientific research priorities to European governments, has just entered the Einstein telescope, a huge next-generation detector of gravitational waves the cost of which should be around 1.9 billion euros, in road map of the projects considered valid and to be continued.

Although the operational phase, at the moment, is still quite far away, it is still a first step towards the actual construction of the instrument, which should be the largest gravitational wave detector never built, equipped with a sensitivity up to 10 times higher than its predecessors and potentially able to help us seek answers to the great still open questions of cosmology and physics, including the existence and nature of dark matter and energy and the reconciliation of general relativity e quantum mechanics.

What are gravitational waves

Small review of physics. The gravitational waves I’m a perturbation of space-time which originates as a result ofacceleration of one or more bodies with mass (two black holes or two stars in rotation, for example), propagates at the speed of light and locally modifies the geometry of space-time itself.

Their existence derives directly from the equations of general theory of relativity formula da Albert Einstein over a century ago, but it was necessary to wait until 2015 to observe them directly: their effect is extremely weak, and therefore almost always hidden by other external perturbations. The detection of gravitational waves requires extremely sophisticated and sensitive measuring devices, the so-called interferometri, tools capable of measuring the temporal discrepancy in the path traveled by two waves of light.

In particular, an interferometer it is a structure composed of two arms of equal length, one perpendicular to the other, to form one L. When a gravitational wave hits the instrument, the associated perturbation is expected to cause light to take longer to travel one arm than the other. When the instruments register a time difference of this type, the alert is launched possible passage of a gravitational wave. To give an idea of ​​how weak these perturbations are, consider that the interferometers must be able to detect a time difference equal to the displacement of the diameter of a hair over a distance between the Sole e Alpha Centauri, that is, over four light years.

The discoveries of interferometers

Despite these enormous difficulties, in 2015, as we said, the two interferometers of the experiment aLigo (of Hanford e Livingstone), whose collaboration also includes the Italian scientists of the experiment Virgo, in Cascina, they managed to reveal the first gravitational wave signal ever picked up by humans, issued by two black holes that have merged with each other.

This first historical revelation was followed by others: two years later, the eyes of aLigo, Virgo and the Eso observatory in Chile again observed a signal of gravitational waves, generated however this time by the collision of two neutron stars. In some ways, this was an even more important discovery, since, unlike black holes – which emit no radiation – neutron stars are accompanied by the emission of light radiation and heavy elements, including gold, platinum and uranium, and thus provide an invaluable mine of data useful for improving our understanding of the Universe.

The scientific community, far from paying, has continued to look forward: in truth, as early as 2004, more than ten years before the 2015 revelation, two scientists, the German Harald Lück, of Max Planck Institute for Gravitational Physics, and Italian Michele Punturo, research manager ofInfn of Perugia, they began to think of a new generation detector, even bigger, more powerful and sensitive than his colleagues. The Einstein telescope, precisely.

“With the detectors we have today”, says Punturo, who is co-chair of the management committee of the Einstein telescope and the Italian project manager, “We can only see a ‘slice’ of the Universe, at a relatively limited time distance. Current tools have a physiological limit that does not allow us to look further than 8 billion years after the Big Bang [circa 6 miliardi di anni fa, nda]; the Einstein telescope, on the other hand, will allow us to push us up to the so-called dark age, just 100 million years after the Big Bang, before of the star formation.

A triangle structure

The new detector, Punturo explains, will be a little different from the existing interferometers: it will have triangular shape, rather than a L, and at each vertex of the triangle will be placed two interferometers, for a total of six “Eyes”. Currently they have been identified two possible sites for its construction: one in northern Europe, on the border between Belgium, Holland and Germany, and another in Sardinia, in an area with very low seismic activity and population density, which represents a significant strength because it minimizes external “noise”.

“The Einstein telescope – says the expert – Sara multi-detector e multi-interferometro: in this way it will be possible to locate the source more precisely e decompose the signal into its polarizations. Sensitivity will also greatly increase, which will allow us to study signals in a much higher level of detail than what has been possible up to now, and in this way we can continue to test the theory of general relativity in increasingly extreme conditions. “, which is important to understand if the theory has limits, what are these limits and if and how it can be reconciled with quantum mechanics.

“And to return to the themes of dark matter anddark energy – says Punturo again – the Einstein telescope could help us learn more. There are theoretical models, for example, which predict that space-time, after the Big Bang, has undergone quantum fluctuations that have given rise to non-stellar black holes, and these black holes may have something to do with dark matter. The telescope will also be able to investigate the presence of any assionic fields, another entity that could be related to dark matter. And again: by characterizing gravitational waves with more precision, some modified theories of gravitation could be verified that would make it possible not to introduce dark energy into cosmological models “. In short, there is a whole new physics to be discovered out there. “We have just entered a phase similar to that in which Galileo brought the telescope to his eyes – Punturo concludes -. And we can’t wait to do it “.

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