After three years of upgrades, the Ligo detector is once again picking up waves of spacetime and detecting black hole mergers. What to understand the genesis of the monsters of the cosmos. And maybe even detect small black holes, primordial black holes, which currently only exist on paper.
Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, talks to us today about a great scientific instrument which has just resumed service, the Ligo gravitational wave detector.
franceinfo: This Ligo detector is the one that made it possible to see, for the first time in 2015, black hole mergers?
Mathilde Fontez: Yes, it is a telescope that does not make beautiful images. It can produce sounds: what does it sound like, two black holes colliding? That’s it: not very impressive, compared to the violence of the event. We listen there, one of the biggest cataclysms of the universe. The clash of two monsters, black holes therefore, very massive stars, tens of times more massive than our star, the Sun, but which are concentrated in a much smaller volume: ultra-dense stars, so dense, that ‘they attract everything that passes near them, and do not let it out.
So to capture their presence, astrophysicists had the idea of trying to capture the vibrations they cause in space-time when they merge: the theory predicted that they must vibrate the fabric of the universe herself. It looks like SF, but it’s really serious. The first of these gravitational waves were discovered in 2015.
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And there, the gravitational wave detector resumes a new observation campaign?
Yes, between 2015 and 2020 it detected 90 “events”, that’s what astrophysicists call them. 90 black hole mergers, and also neutron star mergers – ultra-dense stars, but less than black holes. They also saw mergers of black holes AND neutron stars. In short, they began to draw up a bestiary of these cosmic monsters. With two detectors: Ligo, in the United States then Virgo, in Italy.
But there was still background noise that disturbed the observations. The detectors were turned off to reduce this background noise. This consists in lengthening the tunnels in which circulates the laser beam which makes it possible to capture this tiny vibration of space-time – these tunnels are several kilometers long, they are capable of highlighting a shift smaller than a particle, smaller than a proton. And that’s it: Ligo has just returned to service. And Virgo should go hunting again at the end of the summer, or in the fall.
Are we going to “see” black holes again?
Yes, and at a breakneck pace. Ligo should pick up signals every two – three days thanks to this increase in precision. What to study monsters, understand how they are formed. And perhaps even discover a new kind of black holes, smaller for example, primordial black holes, which would have formed at the very beginning of the universe.