Black hole hunters prove Stephen Hawking was right
The discovery, which comes ten years after the detection of the first gravitational waves, helps to understand these matter-eaters.
GenevaBy analyzing gravitational waves from the merger of two black holes located 1.3 billion light-years away, scientists from the international LIGO collaboration (from the English laser interferometer gravitational-wave observatory) have been able to prove a theory developed by Stephen Hawking more than forty years ago. The British physicist, who died in 2018, hypothesized that the black hole resulting from the merger of two matter-guzzling black holes would necessarily be larger than the sum of the sizes of the two originals.
According to gravitational wave observations detected on January 14, the initial black holes would have a combined total mass of about 240,000 square kilometers, equivalent to the surface area of the United Kingdom. After the merger, the resulting black hole was observed to have a surface area of about 400,000 square kilometers, thus confirming Hawking's prediction. "This is a very important discovery, as it is the most precise test we have made of Einstein's theory of general relativity," explains Giada Caneva, a doctoral student at the Institute of High Energy Physics (IFAE) and one of the lead authors of the study published in the journal Physical Review Letters.
The discovery came ten years after the detection of the first gravitational waves, on September 14, 2015, and seven years after Hawking's death. Following the discovery, the leaders of the LIGO collaboration, Reiner Weiss, Kipp Thorne, and Barry Barish, received the Nobel Prize in Physics in 2017. Since the gravitational wave detectors began operating, some 300 signals have been identified from the merger of two black holes, a merger of two black holes, and two neutron stars. This has allowed us to better understand these types of processes, apparently so common in our universe.
"Gravitational wave detectors allow us to better understand the population of black holes in the Universe," explains Mario Martínez Pérez, an ICREA researcher at IFAE, one of the leading research centers involved in the study. Over the past decade, scientists and engineers have progressively refined detectors, opening a window to the observation of a large number of new phenomena. Detectors like LIGO are now capable of detecting changes in space-time one ten-thousandth the width of a proton, equivalent to about 700 trillion times smaller than a human hair.
Simple and at the same time complex
This discovery also suggests that black holes, despite their apparent complexity, are actually very simple astronomical objects. "You can describe a black hole only with its mass and spin, or rotational speed," explains Caneva, who adds that these characteristics are closely linked to gravitational wave vibrations and can be easily measured. "If you know the mass and spin of a black hole, you know its size," concludes Martínez.
Although there had been indications since 2019 that Hawking's law of black holes was correct, it was an increase in the detector's precision that finally confirmed it. This discovery could have important implications for understanding how gravity works at the microscopic level, or even for developing a quantum theory of gravity. "With gravitational waves, we have opened a window to the possibility of detecting quantum effects of gravity," says Martínez.
A multi-colored window into the unknown universe
Despite still being in its infancy, the detection of gravitational waves has become an essential source of information about the Universe. The IFAE, located at the Autonomous University of Barcelona, is one of the main coordinating centers for the project. "We are preparing the third generation of interferometers with the European Einstein Telescope," explains Martínez. "With this telescope, we will be able to detect a million black holes every year," he concludes.
Thanks to all this information, astronomers and astrophysicists are a little closer to answering some of the most fundamental questions about the origin, composition, and future of the Universe. The window into the cosmos has just opened.
