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Brazilians build a telescope to detect gamma rays from the universe (17 notícias)

Publicado em 04 de agosto de 2022

Astronomers from Brazil, Italy and South Africa have begun installing the first of nine Cherenkov telescopes in the network at the Observatório del Teide in Tenerife, Spain. ASTRI mini-array. Together, they will be able to detect the highest energy radiation produced in the Universe: gamma rays.

Installation of the complete instrument array should be completed by the second half of 2023, and the first astronomical images should be taken in 2024. The group is responsible for building three of the nine telescopes.

Brazilian researchers have participated in all stages of the first telescope, supported by Fapesp.

“Brazil’s participation in this project is of great strategic importance for Brazil because it allows the country to enter the development of instrumentation for multifrequency astronomy”, says Elisabete de Gouveia Dal Pino, professor at the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo. Paulo (IAG-USP) and coordinator of the project.

“The country already has a certain tradition in developing instrumentation for optical and radio telescopes and is now starting to participate in gamma-ray astronomy. In this way, we are covering the frequencies of the spectrum from radio to gamma-ray.”

The ASTRI Mini-Array is a set of nine Cherenkov telescopes, with a diameter of four meters each, whose structure will be the same used in the “small size telescopes” (SSTs) that will make up the Cherenkov Telescope Array (CTA), the largest world’s gamma-ray astronomical observatory — a collaboration in which Dal Pino’s group also participates.

What are gamma rays?

With an estimated cost of 400 million euros (R$ 2.1 billion) and the participation of 31 countries (including Brazil), the CTA should be formed by a network of about 100 Cherenkov-type telescopes, capable of detecting and generating images of showers of highly energized light particles produced when gamma rays from space strike the atmosphere.

Upon reaching Earth, gamma rays collide with air molecules and give rise to subatomic secondary particles (electrons and positrons), which fall in the form of cascades, also known as particle showers.

These high-energy particles can travel faster than the speed of light, giving rise to a blue flash similar to a shock wave produced by a supersonic plane as it breaks the sound barrier.

The effect was named “Cherenkov radiation or light”, in honor of the Russian physicist Pavel Cherenkov (1904-1990), who discovered it experimentally. That’s why the telescopes were so named.

“The possibility of looking at the Universe in this extreme range of the spectrum was only possible recently through Cherenkov radiation sensitive water tanks installed at the HAWC Gamma Ray Observatory in Mexico and the LHAASO [sigla em inglês de Grande Observatório de Chuveiros Aéreos de Alta Altitude, situado na China]. But the signals obtained by these means are of low resolution. Therefore, it is not possible to be sure about the source of the captured signal,” said Dal Pino.

higher resolution

According to the researcher, the CTA will increase the resolution of these sources by up to ten times. This will be possible due to the collection area of ??the telescope array and a combination of three classes of Cherenkov telescopes of different sizes, spread over two sites — the largest of which is at Cerro Paranal, at the European Southern Observatory (ESO) in the Atacama (Chile), and another at the Los Muchachos Observatory, in La Palma, Canary Islands, Spain.

At Cerro Paranal, in the first phase of construction, 14 medium-sized telescopes, measuring 12 meters in diameter, and 37 small-sized telescopes, measuring 4 meters in diameter, will be distributed over an area of ??approximately three square kilometers. This set will be aimed, above all, at recording more energetic and very luminous events in the Milky Way.

In La Palma, in the Canary Islands, in this first stage, along an area of ??about 0.5 km², four large telescopes, with a diameter of 23 meters, and another nine medium-sized ones, focusing on observation of less energetic and less luminous extragalactic events.

Larger telescopes will be aimed at capturing the phenomena that produced lower, low-light energies. The smaller ones will have the opposite function, of observing extremely energetic and luminous events. And those of intermediate size will bridge the gap between the two extremes.

extreme energy

Through a project also supported by Fapesp, another group of Brazilian researchers, led by Luiz Vitor de Souza Filho, a professor at the São Carlos Institute of Physics at USP, developed the metallic structure used to position the camera of the medium telescopes.

“With this configuration of telescopes with three different sizes, it will be possible to observe gamma radiation in a very wide energy range, between 20 gigaelectron volts (GeV) and 300 teraelectron volts (TeV)”, explains Dal Pino.

According to the researcher, all the testing, which is now beginning with the ASTRI telescope array being installed in Tenerife, in collaboration with Italian and South African astronomers, will be very useful for CTA. “The testing will make it possible to make changes to correct any small structural errors.”

The construction of CTA Norte, on Cerro Paranal, began before the Covid-19 pandemic and that of the South, in Spain, was scheduled to start this year. The health crisis, the eruption of the Cumbre Vieja volcano in the Canary Islands in September 2021, and, more recently, the war in Ukraine, however, contributed to delaying the project.

“In recent years, a series of events have taken place that have affected the CTA’s schedule. The war in Ukraine, for example, has reduced supply and contributed to increasing the price of steel, since much of the metal used in Europe comes from the country “, explained Dal Pino.