A new study led by astrophysicist N.V. Krishnendu from the University of Birmingham suggests that next-generation gravitational wave detectors could detect the first black holes formed shortly after the Big Bang. These primordial black holes are thought to have originated from the collapse of Population III stars—massive, early stars formed from pure hydrogen and helium. These stars, which no longer exist today, are believed to have collapsed into the earliest black holes, some of which may have merged, producing gravitational waves. Current gravitational wave observatories, like LIGO in the U.S., Virgo in Italy, and KAGRA in Japan, have detected about 400 events since their first discovery 11 years ago. However, they are limited in detecting events older than 8 billion years due to their sensitivity to high-frequency gravitational waves. To detect signals from the earliest black hole mergers, new observatories such as the Cosmic Explorer (CE) in the U.S. and the Einstein Telescope (ET) in Sardinia are being planned. These future detectors will have longer arms and greater sensitivity, allowing them to pick up lower-frequency gravitational waves. Gravitational waves from the early universe would be stretched by the expansion of the universe, making ancient black holes appear more massive and their signals lower in frequency. For example, a pair of black holes each about 30 times the mass of the Sun merging shortly after the Big Bang would appear as a much larger binary system—around 1,100 times the mass of the Sun—to current detectors. The study used advanced Bayesian supercomputer simulations to model realistic Population III stars and assess the ability of CE and ET to detect mergers that occurred more than 13.54 billion years ago. The study found that a detector capable of measuring vibrations at 5 Hz could detect the early stages of black hole mergers, providing more detailed information about the process. A detector with a sensitivity of 10 Hz would only detect the final moments of the merger. The simulations also indicated that the new detectors could measure the actual mass of ancient black holes with an accuracy of about 12%, helping scientists better understand how supermassive black holes grew in the early universe. Additionally, these detectors could locate merging black hole pairs within about 60 square degrees in at least 60% of cases, which, when combined with data from radio telescopes like the Square Kilometer Array, could reveal connections between black holes and other early universe phenomena. However, building these advanced detectors will require overcoming major engineering challenges.