The detection of gravitational waves in 2023 revealed a cosmic event that seemed to overturn known laws of astrophysics, leaving scientists puzzled by a collision between massive objects.
These waves, captured by ground-based observatories, came from the merger of two black holes located about seven billion light-years away, whose masses and high rotation contradicted established models. According to current theories, such black holes, with masses of 100 and 140 times that of the Sun and spinning nearly at the speed of light, should not form from massive stars, whose only known end is an explosion as a "pair-instability supernova" that scatters all the star's matter.
Artist's representation of two black holes orbiting before their merger. Scientists have solved the mystery of a collision considered impossible.
Credit: NASA Researchers at the Flatiron Institute undertook to solve this mystery by developing simulations that trace the evolution of progenitor stars, from their formation to their death in supernovae. They integrated an often overlooked element: magnetic fields, which play a key role in post-collapse dynamics. This approach made it possible to model how rotation and magnetic forces influence the residual matter around nascent black holes.
The simulations showed that, in the case of rapidly rotating stars, magnetic fields can expel part of the matter at speeds close to that of light, thereby reducing the final mass of the black hole. This mechanism explains why intermediate-mass black holes, previously considered forbidden, can actually form without requiring prior mergers, which would have disrupted their rotation.
This discovery establishes a link between the mass of black holes and their rotation rate, depending on the strength of magnetic fields. Strong fields lead to lighter and slower black holes, while weak fields favor more massive and faster-spinning objects. This correlation opens new perspectives for testing astrophysical models through observations of gamma-ray bursts associated with these formations.
The work, published in
The Astrophysical Journal Letters, offers an elegant explanation for a previously inexplicable phenomenon, highlighting the importance of magnetic factors in stellar evolution. This advance could help better understand the formation of compact objects in the Universe.
Diagram illustrating the formation of "forbidden" black holes leading to an "impossible" collision.
Credit: Lucy Reading-Ikkanda/Simons Foundation Gravitational waves
Predicted by Einstein's theory of general relativity, gravitational waves are disturbances in spacetime caused by violent cosmic events, such as mergers of black holes or neutron stars. They propagate at the speed of light and can be detected using interferometers like LIGO and Virgo, which measure tiny variations in distance. These observations have opened a new window on the Universe, making it possible to study otherwise invisible phenomena, such as collisions of compact objects.
The detection of gravitational waves has revolutionized astronomy by providing direct evidence of the existence of black holes and confirming key aspects of fundamental physics. These data help refine our understanding of the dynamics of binary systems and extreme processes in the cosmos.
Future missions, like the space-based detector LISA, promise to extend this capability to lower frequencies, exploring older or more massive events. This continuous progress enriches our knowledge of the evolution of the Universe and the laws that govern it, linking observations to more robust theories about gravity and matter.