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Virgo will join O4 early 2024

The Virgo Collaboration updated the scientific community last week on the progress of the Virgo detector commissioning, in view of joining the fourth observing run (O4) already undertaken by the two US LIGO interferometers in mid-2023.

Over the summer months, Virgo researchers successfully completed important and delicate hardware work, including the replacement of the mirror located at the end of the interferometer’s north arm. These interventions succeeded in eliminating some well-identified excess noise, but failed to mitigate the broadband noise, which significantly limits the sensitivity of the interferometer, particularly around 100 Hz.

Furthermore thanks to a strenuous and painstaking work of noise hunting and commissioning, the sensitivity of the detector has steadily increased and reached 35 Megaparsecs with the interferometer in a stable set-up. 

The Scientific Collaboration has therefore decided to extend the commissioning phase of the experiment until the end of 2023. The aim is to more clearly identify the origin of the noises that continue to limit Virgo’s sensitivity, and therefore maximize it. 

In any case Virgo will  join the fourth run of observations within March 2024. The exact date will be defined taking into account LIGO and KAGRA’s plans, to allow all interferometers in the network to operate together and to maximize the scientific output. 

“On the one hand we would like to get as close as possible to the sensitivity target of 60 Mpc that we had set ourselves,’ said Gianluca Gemme, INFN researcher and spokesperson of the Virgo Collaboration, ‘but on the other hand we cannot give up the scientific contribution that Virgo could already make by jointly taking data with LIGO and KAGRA. In our opinion, ending the commissioning phase by March 2024 is the best compromise between these two different requirements.”

Although scientific data are currently provided by the two US LIGO detectors, these are shared and analyzed jointly by hundreds of LIGO, Virgo and KAGRA researchers who are actively engaged in this work as well as in processing the scientific results.  

“We are confident” declared Gemme “that with the contribution of Virgo’s data, we will be able to better define and localize possible events of particular astronomical interest next year. These events may have electromagnetic counterparts that can be detected with optical telescopes. The nature and distance from Earth of such events are, of course, unpredictable.”

While the commissioning and preparation phase for O4 continues, the Virgo collaboration is also engaged in preparations for the next O5 science run, scheduled to start in 2027. “The difficulties we encountered during the preparation for O4 and the lessons we learned will be very useful for us to better prepare for O5,” Gemme emphasizes “ and hopefully ensure an even greater impact of Virgo on gravitational wave science”