The Noema telescope dedicates its 12 antennas to view the cold universe

For the uninformed hiker launching an attack on the Bure Plateau in the Dévoluy Alpine Massif, arriving at their destination can be surprising. After climbing a steep slope, he discovers at an altitude of 2,550 meters 12 parabolas of 15 meters in diameter facing the sky. If he waits a little, he will even be able to see them moving in unison, pointing at a new invisible target in the azure sky. They make up the Noema observatory (NORth Extended Millimeter Array), the most powerful millimeter radio telescope in the Northern Hemisphere. This Friday, September 30, 2022, it officially celebrates its transition from 6 to 12 departments after eight years of work.

Watch the stars be born or die

This flagship of Iram (Institute of Millimeter Radio Astronomy), which also has an antenna of 30 meters in diameter at Pico Veleta in southern Spain, observes the universe in a wavelength range from 0.8 mm to 3.5 mm, i.e. a frequency of 80 to 350 gigahertz. “This corresponds to the “light” emitted by the cold universe, just a few degrees above absolute zero [-273°C]summarized for Science and the Future Frédéric Gueth, Deputy Director of Iram. These are the huge molecular clouds that stretch between the stars. Noema, in its previous configuration, and Iram have thus discovered almost half of the 120 molecules identified in the interstellar medium. The millimeter domain also reveals nascent stars in their cocoon of gas, or dying after they have ejected their envelope of gas.” Noema also tracks very distant galaxies, even if they are not icy. As these move away from us, all the more rapidly as they are far away (a consequence of the expansion of the universe), their light is strongly shifted towards long wavelengths. Although they emit in the visible, we therefore see them within radio waves. The instrument thus aims to capture galaxies that are more than 13 billion light years away, which is very close to the Big Bang at 13.8 light years. Noema also observes denser galaxies whose gas she can map, thus studying their evolution and dynamics.

Timelapse of the Noema radio telescope. Credit: Xavier Cuvelier/IRAM

Upcoming images of M87* and Sgr A* black holes

Finally, Noema is part of the collaboration Event Horizon Telescope (EHT), which in 2019 published the first image of a black hole, M87* in the galaxy of the same name, and Sgr A* in the Milky Way. “In this context, the instrument participated in the measurement campaigns in April 2021 and April 2022continues Frédéric Gueth. It will take several months to analyze the results and combine them with results from other EHT instruments, but we already know that the data is of excellent quality.” By going from 6 to 12 antennas, Noema has multiplied its resolution by 4 and its sensitivity by 10. The instrument is thus able to distinguish smaller and darker objects than before. It could detect a mobile phone over 500 km away. For this, it uses the principle of interferometry. The 12 antennas observe the same target. A supercomputer made especially for Noema, “Polyfix”, is responsible for combining the data from each antenna, a titanic task. “In one day, Noema generates as much data as all the internet traffic in France at the same time”, illustrates Frédéric Gueth. The processing makes it possible to obtain the same image as that produced by a single antenna with a diameter equal to the distance between the two most distant antennas. In this little game, Noema can walk up to 1.7 km, because the 120-ton giants travel on rails thanks to electric motors. It is therefore possible to change their configuration according to the astronomers’ needs and zoom in on an object, for example by separating the antennas from each other.

A complementary instrument to James Webb

At a time when the whole world is contemplating the breathtaking images of the James Webb Space Telescope, radio astronomy provides spectra, density maps: not the kind we draw posters from. But Noema’s team is uninhibited. In the observation of the universe, the two instruments play on complementarity, as Frédérique Gueth explains. “When JWST observes a distant galaxy, it can only provide an estimate of the distance that separates us from it, which is called the redshift. Radio astronomy is needed to provide an accurate value of this fundamental datum.” At the beginning of autumn, Noema, who can observe day and night, impatiently awaits the arrival of winter and its long icy nights, the most conducive to observation. Hikers seduced by the majesty of the site will have no trouble imagining how much closer the universe must appear here, with or without a telescope…

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