Virgo detector postpones its new round of gravity wave observations for now

10 May 2023

The Virgo detector for gravitational waves in Italy will not yet participate in the fourth round of observations by the LIGO-Virgo-Kagra consortium starting end of May. The sensitivity of the instrument is not yet optimal.

This has been announced by Virgo’s management. The new observation round O4 will begin May 24 and continue for a year and a half. The two LIGO detectors in the U.S. and the Kagra detector in Japan will start taking data in O4. Virgo is planning to join later.

Technici aan het werk bij de Virgo-detector voor zwaartekrachtsgolven in Pisa, Italiƫ.

Virgo is an Italian-French-Dutch observatory that can measure vibrations from the universe with laser beams in two arms three kilometers long, perpendicular to each other. The instrument near Pisa has been undergoing a series of upgrades.

Despite the effort of the commissioning team and the collaboration, the desired sensitivity has not yet been achieved. More recent tests have given clear indications that the current limitation is related to technical problems on two of the interferometer’s main mirrors.

It was decided not yet to participate in the new round of measurements, but to first insert an extraordinary round of maintenance. This will involve opening the facility’s vacuum towers, in which the mirrors are suspended vibration-free. Preparing and opening the vacuum system is likely to take weeks of work.

“Until we break the vacuum to look directly at the components of the interferometer, we don’t know 100 percent what the problem is,” said Virgo spokesperson Gianluca Gemme.

According to Gemme, only after the intervention can it be indicated when Virgo will be able to start participating in the O4 observing round. To do so, the ultra-high vacuum must first be restored and numerous tests are required.

In the coming months, Virgo scientists will work on the technical issues, as well as co-study and analyze the new measurements from LIGO and Kagra. The detector in Japan is likely to stop taking data after some time for further improvements.

In 2017, the LIGO-Virgo collaboration recorded the first ever gravitational wave coming from colliding black holes in the universe. In the upgrades since 2020, Virgo has been fitted with a new so-called filter cavity. That complicated optical device, designed and partly funded by Nikhef, helps to reduce random and interfering quantum variations in the laser beam in the detector.