Astronomers have been tracking it for a quarter of a century: the background noise emitted by the whirlwind of gigantic black holes has been identified thanks to a novel technique for detecting gravitational waves, which opens “a new window on the Universe”. These results, unveiled on Thursday, are the result of a vast collaboration of the largest radio telescopes in the world. They managed to capture this vibration of the Universe with “the precision of a clock”, enthuse the authors of the work published simultaneously in several scientific journals.
Predicted by Einstein in 1916 and detected a hundred years later, gravitational waves are tiny distortions of spacetime, 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.
A much more time-stretched signal betrays a larger-scale phenomenon, captured by a network of radio telescopes (from Europe, North America, India, Australia and China) of the International Pulsar Timing Array consortium (IPTA). We are talking here about gravitational waves generated by black holes of “several million to several billion times the mass of the Sun”, Gilles Theureau, astronomer at the Paris Observatory-PSL, who coordinated the work, told AFP. on the French side.
To detect these waves, scientists used a novel tool: Milky Way pulsars. These stars have the particularity of having a mass of one to two Suns, compressed in a sphere of about ten kilometers in diameter. At each turn, the pulsars send out ultraregular “beeps”, which make them “remarkable natural clocks”, explains Lucas Guillemot, from the Physics and Chemistry of the Environment and Space Laboratory (LPC2E) in Orléans.
What is the source of these waves? The preferred hypothesis points to pairs of supermassive black holes, each larger than our solar system, “ready to collide”, develops Gilles Theureau. Antoine Petiteau describes two colossi that “circle around each other before merging”, a dance that causes gravitational waves of “a period of several months to several years”.
Continuous background noise that Michael Keith of the European network EPTA (European Pulsing Timing Array) likens to a “noisy restaurant with lots of people talking around you”. The measurements do not yet allow us to say whether this noise betrays the presence of a few pairs of black holes or of an entire population. Another hypothesis suggests a source at the very earliest ages of the Universe, when it experienced a so-called period of inflation.
“We are opening a new window on the Universe”, welcomes Gilles Theureau. “We are adding a new range of information vectors”, complementary to the research of Ligo and Virgo, which operate on different wavelengths, abounds Antoine Petiteau. This could in particular clear up the mystery of the formation of supermassive black holes.
The studies will however have to be deepened to claim a fully robust detection, hoped for within a year. The absolute criterion being “that there is less than a one in a million chance of this happening by chance”, point out the Paris Observatory, the CNRS, the CEA and the universities of Orléans and Paris-Cité in a communicated.
