In 1965, when she discovered that she could not access the Monte Palomar telescope, barred to women for – official reason – “the lack of female toilets in the observatory”, Vera Cooper Rubin he resolved the matter by hanging a figurine of a stylized woman at the entrance to the men’s restroom. To be fair, someone else claims that she handwrote “Wo” in front of the existing “Men” on the door.
Be that as it may, Rubin was not only the first astronomer to have since full access to the telescopeexploited it to the fullest by shattering not only the taboos, but also all astronomy: it is to her that we owe the discovery of the existence of galactic dark matter“one of the most extraordinary results of astrophysics of the last century” writes Patrizia Caraveo in hers Star Messenger 2.0.
“Thanks to his results we now know that 90% of the matter in our galaxy (and all others) does not emit radiation that can be measured by our instruments. We are dominated by matter that can be weighed but not seen. We do not know from which particles this so important, so pervasive and so dark mass is formed”.
To answer the unknowns raised by Rubin, tackling one of the major challenges of contemporary astrophysics – investigating energy and dark matter to understand their role in expansion dynamics of the Universe and why it is accelerating -, in July the European Space Agency (ESA) will send into orbit Euclidthe most complex scientific mission in progress.
A dark scrutiny
Rib 1.4 billion euroswill lead around the so-called Lagrangian point L2, 1.5 million kilometers from the Earth, a telescope with a 1.2-meter mirror in diameter and two scientific instruments, the VISible Instrument (or Vis) and the Near Infrared Spectrometer Photometer (Nisp), with the aim of produce a map large-scale view of the three-dimensional structure of the Universe by studying galaxies up to distances of 10 billion light years from us, to obtain information on the energy and dark matter that constitute it (70% and 25% respectively). In particular, it will make it possible to detect its distribution in extra-galactic space, i.e. outside the Milky Way.
“We will look at the invisible” – explains Giuseppe Racca, program manager of the mission for ESA. The engineer is in the facilities of the satellite prime contractor, Thales Alenia Spacein Cannes, where Euclid has just passed final acceptance trials before being shipped to Cape Canaveral, Florida, from where it will be propelled across the sky by a SpaceX Falcon 9.
“Euclid’s uniqueness lies in the ability to look with unprecedented precision 36% of the Universe”that is, the part not obscured by our own galaxy. “It means observing 15 thousand square degrees to understand what is happening outside our galaxy, an operation that will require six years – the nominal duration of the mission – and will use a wide angle which, unlike all the others, will not distort the images, but will restore them sharply. This is Euclid.”
It is difficult for those who are not experts to grasp the scientific relevance of these objectives. It would then be appropriate to remember that, at the moment, we do not know what dark matter and dark energy are. However, based on the dominant cosmological model, called “Standard”, it is suspected not only that they pervade most of the cosmic immensity, but can also explain some experimental evidence that is wholly or partly incomprehensible, for example why the Universe is in accelerated expansion.
In other words, and with a good deal of simplification, the existence of a mysterious type of matter and energy today is the only way to explain the differences between the behavior of some celestial bodies and the Standard Model.
“Ours will be indirect reliefs – explains Paolo Musi, Euclid program manager for Thales Alenia Space – the dark matter interacts with the visible Universe only through gravity. OWe will observe the deformations on the visible part of the Universe caused by the invisible.
This way we could figure out where dark matter is concentrated, in which direction and at what distance from the Earth, ie at what ‘temporal’ distance: in fact, the farther you look in space the more you go back in time.
The distribution will be the first clue as to what dark matter might be: is it evenly distributed? In bubbles? Is it in all galaxies? This characterization will allow us to discriminate between the various theories”.
Europe and Italy at their best
Results that can only be obtained thanks to a project that is innovative in many respects and the result of one of the most extensive cooperation at European level. Second “Medium” (M2) class mission of the ESA Science Programme, Euclid was approved by the Science Program Committee in June 2012 and developed thanks to the collaboration of 80 companies and a consortium of 300 scientific institutions, for a total of over 4 thousand people involved from 21 different countries. Together with France and Great Britain, Italy is the main protagonist of Euclid thanks to the involvement of its manufacturing excellence and the support, in the first place, of ASI, theItalian space agency.
Thales Alenia Space Italia (joint venture of Thales, 67%, and Leonardo, 33%) is prime contractor for the construction of the satellite – role, for the telescope, covered by the French Airbus – and heads an industrial consortium made up of the major European space companies. In collaboration with the National Institute of Astrophysics (Inaf) and with the National Institute of Nuclear Physics (Infn), the Italian Space Agency led the industrial team that designed and created the contributions to the instruments, a temporary association of companies with Ohb Italia as agent and Sab Aerospace and Temis as principals.
The agency, which has entrusted Altec with the creation of the Italian scientific data center for the mission, will also support research institutions for activities in the Science Working Groups, and will support INAF in leading the scientific ground segment (or SGS), for the development of the on-board software of the two instruments.
“As a wholethe car is new – specifies Musi, also recalling the participation of NASA, which supplied the detectors for the Nisp instrument – among the technological peculiarities of Euclid there are the silicon carbide optics, an extremely light and stable material, almost non-deformable by temperature. The same technology has been used in a few mirrors in the past, but Euclid’s is the largest. On the other hand, the system assigned to aiming the telescope is unprecedented, capable of guaranteeing a precision never reached before: it uses a ‘guide sensor’ and 12 micro-thrusters with cold nitrogen – both contributions by Leonardondr – which with small releases of gas (at 10 microNewtons) are able to contain the maximum oscillation of the telescope within 20 microdegrees and for 700 seconds. A kind of spatial ‘freeze image’ of more than 10 minutes”.
And an exhibition period capable of reaffirming another uniqueness of Euclid, clear in comparison with the two most famous prodigies of space observation, the more than thirty-year-old Hubble and its successor, the James Webb Space Telescope: “Jwst observes objects in the infrared and is aimed, reaches very far and with extreme precision – comments Racca – however it does not have the ambition to make a global map of the Universe. Which is what Euclid is proposing: observe dark matter not around stars, but around galaxies. Billions of galaxies”
With the same precision as Hubble but with a much wider field of view, in one month Euclid will collect the information that its predecessor has collected throughout its operational life. It is expected that between the end of 2024 and the beginning of 2025, it will start releasing one peta byte of data every year. Already impressive, the amount of information could grow to 26 byte request per year when considering the amount of data “scompounded, aggregated, reassembled, analyzed and finally distributed to centers for scientific analysis” Musi adds.
An invaluable treasure chest for the more than two hundred Italian scientists involved in the project, belonging to INAF (mainly the Iaps Institutes of Rome, Oas of Bologna and Iafs of Milan and the Astronomical Observatories of Bologna, Brera, Padua, Rome, Turin and Trieste), to the National Institute of Nuclear Physics and to numerous academic representatives, first and foremost the University of Bologna and Ferrara, the State University of Milan, La Sapienza University of Rome, Roma 3 University, the University of Trieste, Sissa and Cisas.
It is legitimate to ask what the scientific community should expect from the telescope departing in July: “Surprises” answers Musi almost without thinking, who combines his forty years of experience in space with a passion for philosophy. “NIt wouldn’t be the first time that physical theories have been completely revolutionized, which is happening more and more often. The fact that 95% of the Universe is dark suggests that, again, we didn’t understand much”. Vera Rubin would have no objection in this case.