LVK announces an update of the observing schedule

As the third portion of the fourth observing run, O4c, is starting the LIGO – Virgo – KAGRA Collaboration is announcing an upcoming break from observing to dedicate some time to maintenance and commissioning work, and therefore an extension of the O4 run, that was previously planned to end in June. The break will go from April 1st 2025 to June 4th 2025, and the end of the run will be postponed to October 7th 2025.

This break in observation is prompted by the importance of repairing a faulty beam tube gate valve at LIGO Livingston site before this year’s hurricane season and other work on the other detectors of the network that will reduce risk related to the O4-O5 transition. The extension of O4 to early October yields approximately the same amount of calendar observing time as was planned to obtain with the previous June 2025 end date. This new end date accounts for the time lost from this April/May 2025 break, plus that lost from some unplanned interruptions that occurred in 2024, such as a shutter failure at LIGO Livingston and output Faraday damage and laser glitch issues at LIGO Hanford.

“During the fourth observational run, O4, which began in May 2023, 186 significant event candidates were observed, bringing the total number of observed events since September 2015 to 276.” said Virgo spokesperson Gianluca Gemme “The groundbreaking discoveries made in these ten years, from the first detection to the multimessenger observation of 2017, have opened up new avenues for studying the universe and understanding the fundamental physics of black holes and neutron stars. This is a very exciting time for gravitational wave science, we are proud to be part of this effort and we look forward to the new results that the O4 data will bring us.”

At present LIGO detectors can detect the ‘standard’ merger of two neutron stars (BNS range) up to a distance of 160-170 Mpc, and are working with a duty cycle of 65-80%, which represents the percentage of time spent in optimal working conditions, therefore observing. Virgo currently has a duty cycle around 70% and a 50-55 Mpc BNS range.

KAGRA continues noise hunting and cooling the main mirrors. The laser input to the main interferometer is planned to be increased to 10 W to reduce shot noise, in order to improve sensitivity in the high-frequency range. KAGRA expects to rejoin the observing run before the end of O4 with a sensitivity of around 10 Mpc.

Currently, the LIGO – Virgo – KAGRA Collaboration is reassessing its plans for O5, this work is progressing and the current best guess is that O5 could start at the end of 2027, but we expect the plans for O5 to be defined in the first quarter of 2025.