Latest Update on Start of Next Observing Run (O4)
News Release • June 17, 2022
By Kimberly Burtnyk
After over two years of upgrades and maintenance work, LIGO is projecting that its next observing run, O4 (the fourth since the Advanced LIGO instrument came online in 2015) will begin in March 2023. O4 was originally planned to begin in December 2022, but unanticipated delays in completing upgrades and commissioning the instruments is necessitating this later start date.
But the wait will be worth it. LIGO's two detectors in Washington State and Louisiana will be joined by Virgo in Italy and KAGRA in Japan. Virgo has observed alongside LIGO in the past, and was instrumental in localizing the source of the binary neutron star merger in 2017. KAGRA technically joined the LIGO-Virgo network in 2020, but the abrupt end to O3 in March of that year meant that it was not actively observing with LIGO and Virgo for very long.
Importantly, the last 2+ years of major upgrades to LIGO and Virgo instruments in particular will result in much more sensitive detectors, capable of sensing even ‘fainter’ gravitational waves than before—this also means detecting more events than ever before. LIGO projects a sensitivity goal of 160-190 megaparsecs (Mpc) for binary neutron star mergers (that’s how far away LIGO can expect to detect two neutron stars colliding). Virgo projects a target sensitivity of 80-115 Mpc. KAGRA, which employs some unique forward-looking but challenging detection technology, should be running with greater than 1 Mpc sensitivity at the beginning of O4, and will work to improve its sensitivity toward the end of O4. Of course, more violent or larger events, such as black hole collisions, are detectable from much deeper reaches of the Universe, but we use the distance at which we can detect neutron star mergers as a means to describe our sensitivity to all gravitational waves.
LIGO, Virgo, and KAGRA are closely coordinating to start O4 together. One month prior to beginning O4, all sites will engage in a collaborative engineering run to test the upgraded instruments in real time, and test systems required for observing together. There’s always a chance that a detection will be made during an engineering run, so if any candidate events occur, they may be released to the scientific community and studied further. (In fact, LIGO’s very first detection in September 2015 came during an engineering run.)
O4 is expected to last one full year with a one-month break for maintenance in the middle. KAGRA is expected to start observing alongside Virgo and LIGO, and then at some point, step away for commissioning and return to observing with a greater sensitivity toward the end of O4.
Everyone at LIGO (and Virgo and KAGRA!) is eager to start detecting gravitational waves once again and sharing our discoveries with the world. We eagerly await March 2023.
For more detailed descriptions of what's expected in O4, please visit the LIGO Observing Plans page.