New Black Hole Record
In the third observation run, the researchers of the LIGO Virgo team caught a big fish: the most massive black hole to date with 142 solar masses. The discovery of this gravitational-wave event GW 190521 raises new questions.
Two orbiting black holes emit gravitational waves that propagate through the universe at the speed of light. Sooner or later the two must collide, and at that moment the tremors of space-time are particularly violent. For a few years now, physicists have routinely observed such gravitational-wave events. However, the new signal, which the LIGO and Virgo detectors based in the USA and Italy received on March 21,Registered May 2019 was different. The event, called GW 190521, was shorter at 0.1 seconds and, at 60 Hertz, reached a lower maximum frequency than the gravitational wave pulses received to date, as the researchers report in the journal Physical Review Letters. It wasn't like the "chirp" that scientists usually detect, explained Nelson Christensen of France's Center National de la Recherche Scientifique and a member of the Virgo Collaboration in a press release. The researchers use the term "chirp" to describe the characteristic signal with increasing amplitude and frequency, which exponentially falls silent at the moment of the collision - as did the first LIGO event GW 150914, which marked a breakthrough (see SuW 4/2016, p. 24). "This time it reminded us more of a 'bang'; it's the most powerful signal LIGO and Virgo have seen so far." (see picture on next page).
The black holes that triggered this signal were 85 and 66 times the mass of the Sun, respectively, making them more massive than any black hole observed by LIGO and Virgo to date. The researchers conclude this from the signals recorded with LIGO and Virgo. Nine solar masses were converted to gravitational-wave energy in the collision; this is the only reason why the event could be perceived by the detectors. It happened so far from our galaxy that the gravitational waves took about seven billion years to get to us. The associated cosmological redshift is z=0.82.
