Update: a telescope designed to study a mysterious dark energy keeps the hopes of Russian space science | Science

* Update of July 15th at 9:55 am: At 18:31 The Russian Spektr-RG X-ray Observatory was launched on July 13th from the Baikonur Cosmodrome in Kazakhstan. He will begin a 4 year study of the x-ray sky.

The beleaguered space science program in Russia hopes to win a rare triumph this month. Spektr-RG, an X-ray satellite to be launched on June 21 from Kazakhstan, aims to map all of the more than 100,000 clusters of galaxies visible in the universe. Containing up to 1000 galaxies and the mass of a million billion suns, clusters are the largest gravity-bound structures in the universe. Their study is expected to better understand the evolution of the universe and the nature of black energy that accelerates its expansion.

Proposed for the first time more than 30 years ago as part of a Soviet plan providing for a series of ambitious "big observatories" inspired by NASA's Hubble Space Telescope, Spektr-RG was the victim of a large number of "big observatories" inspired by NASA's Hubble Space Telescope. a cost reduction in post-Soviet Russia, short of money. But about 500 million euros of satellites, which will carry German and Russian X-ray telescopes, are reborn at the beginning of the last decade with a new mission: not only looking in the sky for interesting X-ray sources, such as only supermassive black holes gorging themselves with infallible materials. , but to map enough clusters of galaxies to discover what makes the universe vibrate. The new goal meant additional delays. "There have been a lot of ups and downs," said Peter Predehl, head of the team at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, which built the 39, one of the two telescopes of the satellite. "Every time we thought we were out of the wood, a new one happened to us."

Spektr-RG was born in the late 1980s. Glasnost encouraged Soviet researchers to collaborate with their Western colleagues, and studies of SN 1987A, the closest supernova of modern times, had demonstrated the power of X-rays for traceability of such violent events. Rashid Sunyaev of the Moscow Space Research Institute (IKI) has proposed the launch of an X-ray observatory above the Earth's atmosphere, which blocks X-rays. Is rapidly bristling with five telescopes and has involved 20 institutes in 12 countries, including the United States. But after the collapse of the Soviet Union, Roscosmos struggled to keep its Mir space station high and contribute to the growth of the International Space Station (ISS). "They told us that the spacecraft was too big for Russia and too ambitious," said Sunyaev, currently at the Max Planck Institute of Astrophysics Garching. "He just died."

The resurrection began in 2003 with the idea of ​​a smaller mission with an all-sky X-ray monitor built by the UK and the MPE's X-ray telescope, called ROSITA, intended for use in the United States. ISS but blocked by the Space Shuttle Challenger disaster. The new impulse was cosmology. Studies of distant supernovae in the 1990s had revealed that the expansion of the universe was accelerating. The researchers wanted to know more about the dark energy, the mysterious force that provoked it and its variation in space or time. Clusters of galaxies are among the best indicators, says X-ray astronomer Andrew Fabian of the Institute of Astronomy (IoA) of Cambridge, UK. "Clusters are the most massive objects in the universe, the pinnacle of galaxy formation. models."

They are best seen in X-rays because empty spaces between galaxies are filled with gas heated to millions of degrees when galaxies jostle to form a cluster. By mapping the clusters, explains Esra Bulbul of the Harvard-Smithsonian Astrophysical Center in Cambridge, Massachusetts, who recently joined the MPE team, Spektr-RG "will study the evolution of the structure of the universe."

The challenge was to strengthen the capabilities of the existing ROSITA telescope, which could only have 10,000 galaxy clusters. The discussions culminated in an "extended" eROSITA of 90 million euros, funded by MPE and the German Aerospace Center, DLR. It is a set of seven identical telescopes having an effective collection area five times greater than that of the original instrument. Russia and Germany signed an agreement in 2007 with a launch scheduled for 2012.

But the development of the mission has not been smooth. The British instrument has failed to secure funding and has been replaced by a Russian telescope called ART-XC, which will complement eROSITA in detecting the rarer high-energy X-rays. Although harder to collect, high-energy photons are particularly useful for seeing supermassive black holes in the center of the galaxy as they pierce the clouds of gas and dust enveloping them.

The manufacture of mirrors for eROSITA has also proved to be much more difficult than expected. X-rays penetrating into a traditional flat-telescope mirror, their focusing requires cylindrical mirrors that collect X-ray photons as low-angle reflections on internal surfaces. EROSITA's seven scopes each contain 54 gold-plated cylindrical mirrors, nested inside each other, which must be precisely shaped for the photons to focus. Their manufacture proved so difficult that the MPE team had to fire their main contractor at mid-term. "It almost killed us," says Predehl.

The decision to place the telescope in a quiet, gravitationally balanced location beyond the moon, away from the earth's magnetic field, involved hardening the electronics against solar radiation. The incompatibility between German and Russian electronics delayed the launch, as well as problems with the spacecraft's communication system and a modification of the launch rocket.

Now that Spektr-RG is finally ready, the expectations are great. "The numbers are going to be revolutionary," says IoA astronomer George Lansbury, analyzing x-rays in "the big data regime."

It may also be a rare highlight for Russia's major observatory program. Previously, only one had been put into orbit: Spektr-R, a 2011 radioastronomy mission that did not meet expectations and could not be reactivated after a malfunction earlier this year.

Astronomers will face a long wait for the successors of Spektr-RG: the Spektr-UV and Spektr-M ultraviolet telescope, a millimeter-wave radiotelescope. Spektr-UV survived moments of imminent death, the last time in 2014 when Russia's annexation of the Crimea peninsula by Ukraine forced major Ukrainian partners to withdraw. The mission is now to be launched in 2025, but some staff, including a German team providing a spectrograph, have left school, Sunyaev added. Spektr-M, who will come next, is not yet fully funded, he says. And in the meantime, competing telescopes launched by other countries could strengthen the scientific knowledge that Russian missions aim to make.

"Russia is doing everything in its power with the available budget," said Mikhail Pavlinsky, head of Spektr-RG of IKI. He notes that Roscosmos' reduced budget, worth $ 20.5 billion over 10 years, faces many demands. Russia is building the landing system of the European ExoMars rover, which should be launched next year. Like other countries, he hopes to return to the moon with the LG Luna 25 in 2021. For Russian astrophysicists, Pavlinksy says, "It means slow progress. "