He heard background noise from the universe for the first time

Astronomers have been tracking it for a quarter of a century. The background noise emitted by a whirlwind of giant black holes has been identified thanks to an unprecedented technique for detecting gravitational waves, according to research published simultaneously in several scientific journals, Thursday, June 29.

These results are the result of an extensive collaboration of the world’s largest radio telescopes, part of the International Puslar Timing Array Consortium (IPTA). They succeeded in capturing this vibration of the universe by “clock accuracy”the authors of the work got excited.

Predicted by Einstein in 1916 and discovered a hundred years later, gravitational waves are small distortions in space-time, similar to ripples of water on the surface of a pond. These oscillations, which propagate at the speed of light, are generated by violent cosmic events, such as the collision of two black holes. They may be associated with massive phenomena, but their signals are very weak.

A new window on the universe

In 2015, the gravitational-wave detectors Ligo (USA) and Virgo (Europe) revolutionized astrophysics by detecting the very short tremor — less than a second — of collisions between black holes. This time, the signal extended for an even longer period refers to gravitational waves generated by black holes in “several million to several billion times the mass of the sun”Gilles Theureau, astronomer at the Paris-PSL Observatory, who coordinated the work on the French side.

To detect these waves, scientists used a new tool: the Milky Way’s pulsars. Very compact, these stars run themselves at high speed. At every turn, it sends out pulsars “beep” making it super regular “Wonderful natural hours”explains Lucas Guillemot, of the Laboratory of Physics and Chemistry for the Environment and Space (LPC2E) in Orléans. Scientists have included groups of pulsars to get “celestial web” in the meanders of space-time. This allowed them to measure a small perturbation in this ticking property of gravitational waves.

What is the source of these waves? The preferred hypothesis points to pairs of supermassive black holes “ready to crash”Generation of Thoreau develops. Continuous background noise Michael Keith, of the European Network EPTA (European Pulse Timing Array) compares to “Noisy restaurant with lots of people talking around you”. The measurements do not yet make it possible to determine whether this noise is indicative of the presence of a few pairs of black holes, or the presence of an entire population. We open a new window on the universe.Welcome to the Thoreau generation. These studies, which must be deepened, can clarify in particular the mystery of the formation of supermassive black holes.