The scientific collaboration that operates the global network of gravitational wave detectors (LIGO in the USA, Virgo in Italy and Kagra in Japan) has in recent days updated the timetable for the start of the new observing run, previously scheduled for the end of March 2023.
The start will be delayed by a few months, as all the detectors are facing challenges in achieving the expected levels of stability and sensitivity, after the major technological upgrades carried out on them. Researchers are aiming to reach the targets set to ‘switch on’ the experiments within a few months, i.e. by the end of May this year. Moreover, the new observing run, called O4 (it is the fourth since 2015) will last 18 months instead of the initially planned 12 ones.
Since the discovery of gravitational waves, the LIGO and Virgo interferometers have in fact always alternated between data-taking periods of about one year and downtimes for the implementation of technological upgrades, in order to significantly increase sensitivity and thus the rate of observations, which, for example, increased 10-fold from the second (O2) to the third (O3) run.
O4 will be extended to 18 months in order to finalize the development of new mirror coatings to be used in the next upgrade. However, this will also provide the opportunity to increase scientific observations and the probability of relevant discoveries, such as the so-called multi-messenger events, i.e. a joint observation of gravitational waves and electromagnetic signals produced by the same phenomenon. This has been performed so far only once, in the case of the famous neutron star merger detected on 17 August 2017 by LIGO and Virgo.
The targets for detector sensitivity remain unchanged: LIGO aims for a sensitivity of 160-190 Mpc for binary neutron stars, Virgo aims at a sensitivity of 80-115 Mpc, and KAGRA is expected to operate with a sensitivity above 1 Mpc at the beginning of O4 and will work to improve sensitivity to around 10 Mpc around spring 2024.
Achieving this goal will mean a 50% improvement in sensitivity for Virgo compared to the previous cycle of observations (O3), which corresponds to observing a cosmic volume three times larger and switching from weekly to daily detections.
“The new window on the universe is going to be opened again soon by LIGO, Virgo and KAGRA – said the Virgo spokesperson and INFN researcher, Giovanni Losurdo- We are excited to take a further step in our understanding of the cosmos and look forward to the many detections expected in O4”