EI2GYB > ASTRO 19.11.25 12:45l 55 Lines 5721 Bytes #200 (0) @ WW
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Subj: Collaboration completes richest observation run of gravitat
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Collaboration completes richest observation run of gravitational signals to date
The international LIGO-Virgo-KAGRA Collaboration has completed the fourth observation campaign (called O4) of the international network of gravitational wave detectors. Launched in May 2023, the campaign ends after a period of coordinated observations lasting over two years, during which the analysis of the data was also initiated in parallel.
Some 250 new signals were detected in this latest observation run, constituting a significant fraction (over two-thirds) of the approximately 350 gravitational signals detected to date by LIGO, Virgo and KAGRA. The increase in the number of events observed in each cycle is due to the progressive improvement of detector technologies and the resulting increase in their sensitivity.
These developments have led to numerous new discoveries in recent years. Also, some of the most significant results of this latest observational cycle have already been announced and published, contributing to a further deepening of our understanding of the nature of compact binary systems and certain fundamental physical processes in the universe.
"The completion of O4 marks a historic milestone: the longest observing run ever conducted by the global gravitational-wave network," said Gianluca Gemme, spokesperson for the Virgo Collaboration and researcher at the Italian National Institute for Nuclear Physics (INFN).
"Virgo has played a crucial role, contributing to the detection and characterization of numerous signals. The success of the O4 run reflects the strength of international collaboration and the relentless effort of our teams to push the boundaries of such precise and challenging measurements. Looking ahead, we are preparing for major upgrades that will significantly enhance the sensitivity of our detectors, ensuring a new and even greater scientific impact."
An analysis of some of the most interesting events of this latest campaign has already yielded particularly significant results. For example, the analysis of the event called GW250114 allowed scientists to "hear" with unprecedented accuracy two black holes as they merged into one, providing observational evidence for a theorem put forth by Stephen Hawking in 1971 that says the total surface areas of black holes cannot decrease. In this case, the initial black holes had a total surface area of 240,000 square kilometers, while the final area was about 400,000 square kilometers: a clear increase.
Another important outcome, already published in the past months, was the first detection of "second generation" black holes, GW241011 and GW241110, events that present unusual characteristics in terms of the size and rotational orientation of black holes, which can be explained by hypothesizing that they are themselves the result of previous mergers. In other words, these would be systems formed in extremely dense and 'chaotic' cosmic environments, such as star clusters, where black holes are more likely to collide and merge repeatedly.
A further significant detection, GW231123, marks the observation of the most massive black hole merger to date, which produced a final black hole more than 225 times the mass of our sun. An event that challenges our current models of stellar evolution and black hole formation. Of course, other significant results and discoveries are also expected from the analysis of the remaining hundreds of events collected over the last two years, which are currently being carefully examined and will be published in the coming months in a detailed collection: the O4 gravitational signal "catalog."
The LIGO, Virgo and KAGRA interferometers are preparing for a new phase of technological upgrades and testing over the next few years. However, this upgrade will likely be implemented in several stages, with periods of data collection in between and a new observation campaign starting in late summer/early fall 2026 and lasting approximately six months.
Provided by European Gravitational Observatory
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