This sound emitted by the whirlwind of gigantic black holes has been identified thanks to an unprecedented technique for detecting gravitational waves.
Astronomers had been tracking it for a quarter of a century. The background noise emitted by a whirlwind of gigantic 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 (IPTA) consortium. They succeeded in capturing this vibration of the universe with “the precision of a clock”enthuse the authors of the work.
Predicted by Einstein in 1916 and detected a hundred years later, gravitational waves are tiny distortions of space-time, similar to ripples in water on the surface of a pond. These oscillations, which propagate at the speed of light, are born under the effect of violent cosmic events, such as the collision of two black holes. They may be linked to massive phenomena, but their signal is extremely tenuous.
“A New Window to the Universe”
In 2015, the gravitational wave detectors Ligo (United States) and Virgo (Europe) revolutionized astrophysics by detecting the ultra-short quivering – less than a second – of collisions between black holes. This time, a much more time-stretched signal betrays gravitational waves generated by black holes of “several million to several billion times the mass of the Sun”specifies Gilles Theureau, astronomer at the Paris-PSL Observatory, who coordinated the work on the French side.
To detect these waves, the scientists used a novel tool: Milky Way pulsars. Ultra-compact, these stars turn on themselves at high speed. At each turn, the pulsars send “beep” ultra-regular, which make them “remarkable natural clocks”, explains Lucas Guillemot, from the Physics and Chemistry of the Environment and Space Laboratory (LPC2E) in Orléans. Scientists have listed groups of pulsars, to obtain a “celestial mesh” in the meanders of space-time. This allowed them to measure a tiny disturbance in this ticking, characteristic of gravitational waves.
What is the source of these waves? Favored hypothesis points to pairs of supermassive black holes “ready to crash”, develops Gilles Theureau. A continuous background noise that Michael Keith, of the European network EPTA (European Pulsing Timing Array), compares to a “noisy restaurant with lots of people talking around you”. The measurements do not yet make it possible to say whether this noise betrays the presence of a few pairs of black holes, or of an entire population. “We open a new window on the universe”, welcomes Gilles Theureau. These studies, which will have to be deepened, could in particular clarify the mystery of the formation of supermassive black holes.