The international collaboration of the LIGO, Virgo, and KAGRA gravitational wave observatories has reached an extraordinary milestone, detecting its 200th candidate gravitational wave signal during its latest observation run, O4.
This record-breaking discovery, which occurred on 19 March, is believed to result from a merger between two black holes – a celestial event that underscores the tremendous advancements in gravitational wave astronomy.
Compared to previous observational periods (O1, O2, and O3), which collectively identified 90 gravitational waves, the current surge in detections is unprecedented.
The dramatic increase is attributed to significant technological enhancements made between the O3 and O4 observation periods, boosting the sensitivity of the detectors and allowing them to perceive more distant and subtle cosmic phenomena.
Black hole mergers dominate signal detection
Of the 200 recorded signals, the majority are attributed to the merging of black hole pairs millions or even billions of light-years from Earth.
These high-energy events create ripples in spacetime that the upgraded observatories can now detect with greater precision.
While black hole mergers dominate the dataset, detections involving neutron stars – either in neutron star-neutron star mergers or mixed binaries with black holes – remain relatively rare due to the weaker gravitational signals they emit.
The science behind the discovery
Since the commencement of the O4 observation period in May 2023, the network of gravitational-wave detectors has been continuously scanning the Universe for signs of cosmic collisions.
A brief operational pause in early 2024 allowed for the Virgo detector to rejoin the LIGO observatories, further enhancing the network’s detection capabilities.
The current phase is set to continue until October 2025, with another scheduled technical break in the spring to refine equipment and increase sensitivity further.
The scientific community is now deeply engaged in analysing the vast dataset accumulated over the past year and a half. These findings will provide crucial insights into the nature of black holes, neutron stars, and the evolution of the cosmos.
This influx of new information is expected to refine existing astrophysical models and potentially lead to groundbreaking discoveries about the fundamental forces governing the Universe.
A global effort for multimessenger astronomy
In addition to detecting gravitational waves, the LVK Collaboration is dedicated to sharing its findings swiftly with the global scientific community.
Through NASA’s GCN Circulars, astronomers worldwide receive near-instantaneous alerts regarding newly detected signals.
This rapid dissemination enables multimessenger astronomy – coordinated observations using gravitational waves, electromagnetic radiation, gamma rays, neutrinos, and cosmic rays – to capture a comprehensive picture of these cataclysmic events.
A specialised group known as the Rapid Response Team (RRT), comprising over 600 researchers, is responsible for immediately assessing candidate signals.
Their role is to determine whether a detected signal originates from an astrophysical event or terrestrial interference. Using advanced algorithms, they estimate the masses of the merging objects and their approximate location in the sky.
This information is typically made publicly available within just 30 minutes of detection, facilitating real-time collaboration between observatories worldwide.
Validating and refining gravitational wave signals
While each detection is initially classified as a candidate event, further analysis is required to confirm its authenticity.
Scientists employ sophisticated and time-intensive computational techniques to distinguish genuine gravitational wave events from background noise. In some cases, previously detected signals may be reclassified, but overall, the number of confirmed events remains largely stable after a thorough examination.
The future of gravitational wave astronomy
As the O4 observation period progresses, researchers anticipate even more detections, further enriching our understanding of the Universe.
The success of LIGO, Virgo, and KAGRA highlights the significance of international collaboration and technological advancements in detecting gravitational waves.
With future upgrades and expansions planned, the ability to probe the depths of the cosmos will only continue to improve, potentially unveiling new astrophysical phenomena beyond our current comprehension.
