With 12 domes, the Bure plateau radio telescope is complete

And 12 for the domes of the most powerful millimeter radio telescope in the northern hemisphere, located on a high plateau in the Alps, whose observations promise discoveries ranging from the composition of nearby comets to the origin of life in the universe. .

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Employees work near the domes of Iram’s NOEMA radio telescope on September 20 on the Bure plateau in the Hautes-Alpes.

Every visitor to the NOEMA (Northern extended millimeter array) observatory completes the journey on foot and at an altitude of 2,550 meters, leading to an alignment of domes sparkling in the sun in a mineral setting dotted with rare tufts of grass and still virgin snow.

The installation has already allowed “significant advances in astronomy, such as the vision of the hearts of galaxies“, explains Frédéric Geth, astronomer and deputy director of the Institute for millimetric radio astronomy (Iram), in the slight icy wind that sweeps over the Bure plateau (Hautes-Alpes).

Iram was established in 1979 at the initiative of the German Max Planck Institute and the National Center for Scientific Research (CNRS), and was later joined by the Spanish National Geographic Institute (IGN). Its flagship has long been the large Pico Veleta radio telescope in Spain, with a dome 30 meters in diameter.

Size matters in millimeter radio astronomy to pick up extremely weak electromagnetic wave signals. A galaxy, for example, emits these waves in frequencies ranging from X-rays, the most energetic, through visible light, to radio waves, the lowest in energy (millimeters and centimeters).

Radio waves are the universe’scold”, That means “everything but the stars”, and this is the kingdom of NOEMA. Bure’s aluminum domes are only fifteen meters in diameter, but their resolving power lies partly in their number, which has increased from six in 2014 to twelve since this year, and partly in their configuration.

Virtual dome

Mobile, despite their 120 tons each, they are arranged on two tracks that form a T. This is the trick of the observational technique of interferometry: it consists in pointing at the exact same moment the same object in space with several domes that form a virtual dome as large as the distance separating the furthest from each other.

It is then up to the correlator, a modest-looking supercomputer housed in a small room in the observatory, to combine the received signals using skillful calculations to reconstruct a single image.

Winter sees the arrangement of domes stretching out in its wide configuration with a maximum distance of 1.7 km. It is “most important moment of observation when the atmosphere is ideal, with dry, cold and stable air”, explains Frédéric Geth.

Domes of Iram’s NOEMA radio telescope on the Bure plateau, 20 September.

The installation revolves around an impressive maintenance hall, which houses NOEMA’s small control room. A cable car, reserved for equipment, carries the equipment needed to maintain the domes and supply the permanently inhabited base.

“Bricks of Life”

Access to the base is via a corridor that protects against bad weather and snow that will soon cover the plateau. The domes are monitored like milk on a fire, with a heating system so that neither ice nor dew interferes with their observations.

In the control room, André Rambaud, an operator, steers their pointer in front of a bank of monitors. “Let’s go to observe eight galaxies that are ten or twelve billion light years away and that the domes will follow for five hours“, he says with a smile.

The astronomer on duty, Edwige Chapillon, from Iram, chooses the observation order of the projects that have been accepted – up to almost 500 per year -“depending on their nature and weather”. NOEMA’s science is not the most “sexy“, its astronomers agree. Hard to compete with the general public with the breathtaking images of the new James Webb Space Telescope, for example.

But this “amazing time machine“, as Edwige Chapillon, a specialist in extra-galactic observations, calls it, brings decisive progress to the understanding of the universe.

Iram observatories have discovered almost half of the known interstellar molecules, “the brick of life in the universe”, notes the astronomer. And it is thanks to NOEMA that astrophysicists have precisely determined the temperature of the young universe less than a billion years after the Big Bang.

And the IRAM network is part of the Event Horizon Telescope (EHT) collaboration, which brings together the most important radio telescopes in the world (including Alma in the Southern Hemisphere), which produced the first images of black holes. NOEMA joined the network in 2021 and will easily find its place there.


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