First detection of gravitational waves from colossal black holes

2023-06-29 02:00:04
The Nançay radio telescope, in Cher. CNRS

Nestled in the heart of merging galaxies, invisible couples of supermassive black holes make space-time vibrate. European astronomers working with Japanese and Indian researchers have just provided proof of this by detecting, alongside American, Australian and Chinese teams, the gravitational waves produced by these pairs of colossal objects.

In a series of articles published Thursday, June 29, in the journal Astronomy and Astrophysicsscientists from the EPTA (European Pulsar Timing Array) network, which brings together the six largest radio telescopes on the Old Continent, including that of Nançay (Cher), explain how they arrived by diligent observation of a handful of dead stars, to create a detector the size of the Milky Way, sensitive to these signals!

At the origin of this tour de force which opens the way to a better understanding of the origin of black holes and galaxies: the father of the theory of general relativity, Albert Einstein himself, who in 1915 predicted the existence gravitational waves. According to his thesis, any acceleration of a mass in the Universe can generate – if conducted asymmetrically – “waves” which propagate at the speed of light through the cosmos. Vibrations that distort space as they pass, first stretching it, then contracting it before returning it to its original dimensions.

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Ces « rides » of space-time are not a view of the mind. They have been detected more than a hundred times since their discovery in 2015 by the Franco-Italian and American facilities Virgo and LIGO. Giving astronomers the opportunity to confirm the nature of some of the phenomena that produce them: the merger of two stellar black holes or two neutron stars or the absorption of a neutron star by a stellar black hole.

Timing with precision

But if they validated a concept for accessing unobservable events by other means – a black hole emits neither light nor radiation and no matter escapes from it! – , the LIGO and Virgo interferometers – whose results were hailed by a Nobel Prize in Physics in 2017 – were not designed to go further.

“Only sensitive to high frequency gravitational waves, these instruments are blind to others”, explains Ismael Cognard, CNRS research director at the Laboratory of Physics and Chemistry of the Environment and Space (LPC2E) in Orléans. And, in particular, to those created, everywhere in the Universe, by the meeting of duos of other black holes, millions of times more massive than the first: those occupying the center of the galaxies.

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