September/October 2025
By: Jonathan Bratanata, Romano Meijer, Mikhail Korobko, Daniela Trani, Conor Mow-Lowry, Gregory Iaquaniello, Martine Oudenhoven
A lot of things are happening that are relevant for ETO's work. For example, in the gravitational wave community, in the Einstein Telescope Collaboration and in politics. Have a look at these snippets of information on various relevant developments.
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Ten years ago, on 14 September 2015, LIGO made the first-ever detection of gravitational waves: GW150914. This breakthrough has allowed us to study cosmic events not only through light waves or neutrinos, but through the gravitational warping of space itself. Since then, the LVK collaboration (LIGO, Virgo, and KAGRA) has recorded around 300 black hole mergers in total. In the current O4 observing run, the network has already identified over 200 merger candidates — more than twice the number detected across the first three runs combined. The 10-year anniversary of the first gravitational wave detection has been celebrated throughout the community. Read more in the article 'Ten Years Later, LIGO is a Black-Hole Hunting Machine' on the LIGO website, or 'Ten Years of Gravitational Waves' on the EGO website.
The improved sensitivity of the LIGO detectors is exemplified in a recent discovery of a black hole merger referred to as GW250114. This event shows two colliding black holes at approximately 1.3 billion light-years away and 30 to 40 Solar masses. It produced the clearest gravitational-wave signal ever recorded. This clarity let scientists confirm Stephen Hawking’s Black Hole Area Theorem, showing with 99.999% confidence that the total surface area of a merged black hole increases, just as theory predicts. The result also provides further support for Einstein’s theory of general relativity. And perhaps most importantly, it demonstrates how gravitational-wave astronomy now enables deeper tests of the laws of the universe and opens new pathways to studying spacetime itself - an exciting prospect for the Einstein Telescope’s scientific potential. Read more about this signal on the LIGO website, or in LIGO magazine issue 27.
Gravitational wave detectors are not always ‘switched on’ and collecting signals. They follow a long term schedule, during which the so-called Observing Runs are alternated with down time for construction and commissioning, and transitional Engineering Runs in between. The current (second generation) detectors — LIGO, Virgo & KAGRA, have been in the fourth observing run (O4) since May 2023, continuously improving on the sensitivity and stability of the detectors. In summer 2025, a short engineering break was completed and all detectors are now in the final stretch of O4, which will last until the middle of November 2025. Then the detectors will go into a long upgrade period to significantly improve the detectors for O5. Read more about the observing run O4 on the LIGO website.
The cosmic events that are detected through gravitational waves, are registered in the Gravitational Wave Transient Catalog (GWTC). The LIGO-Virgo-Kagra collaboration has now released a new version of this catalog: GWTC 4.0. It contains 128 new significant gravitational wave signal candidates. The LIGO-Virgo-Kagra collaboration is also working on scientific papers to summarise the implications of these detections. Read more about this catalog and the process in the article GWTC 4.0 Updated Gravitational Wave Catalog Released on the LIGO website.
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Germany has confirmed the Einstein Telescope as a national priority by including it in the shortlist of the country’s most promising large-scale research infrastructures. The shortlist, comprising nine selected projects, was announced on 8 July by Federal Research Minister Dorothee Bär, the German Council of Science and Humanities, and representatives of the evaluation committees. The inclusion of the Einstein Telescope marks a significant milestone, as it reflects formal federal-level support for the project and its international relevance. An official statement from the German Einstein Telescope community was published on 9 July to highlight this important development. Read more about the German support on the European Einstein Telescope website.
After their meeting in June 2025, the Einstein Telescope Board of Governmental Representatives (BGR) confirmed that Lusatia in Saxony, Germany is now considered to be an official candidate location for the Einstein Telescope. This follows Lusatia’s earlier expression of interest for becoming an official candidate. Conversations and collaborations with the Lusatia team were already ongoing for some time. This confirmation by the BGR can be seen as a formal step to fully include Lusatia in the procedures, next to Sardinia and the Euregio Meuse-Rhine.
Read: Lusatia officially third candidate location for the Einstein Telescope