2023-07-09 06:00:09
Black holes are among the most captivating celestial objects in the cosmos. Their gravitational force is so strong that not even light can escape. The groundbreaking detection of gravitational waves in 2015, caused by the merger of two black holes, opened up new fields of exploration (Exploration is the act of searching with the intention of discovering something unknown.). Since then, dozens of similar observations have prompted astrophysicists to probe their origins.
A 31.5 solar mass black hole and 8.38 solar mass companion black hole, seen in front of their stellar nursery (computer generated) before the merger.
© Aaron M. Geller/Northwestern CIERA & NIGHT-RCS; ESO / S. Brunier
Thanks to recent advances in the code POSYDON, used to simulate populations of binary stars, a team from the universities of Geneva (UNIGE), Northwestern and Florida (UF) predicted the existence of massive black holes in fusion, of thirty solar masses, in galaxies similar to the OUR. These results, which challenge previous theories, are published in Nature Astronomy.
Black holes are celestial objects born from the collapse of stars whose mass can reach up to several hundred times that of our Sun. Their gravitational field is so intense that neither matter nor radiation can escape them, which makes their detection extremely difficult. Therefore, when the tiny ripples in spacetime produced by the merger of two black holes were detected in 2015, by the Observatory of gravitational waves by laser interferometry (Interferometry is a method of measurement that exploits interference…) (LIGO), these observations have put the scientific world (A scientist is a person who is dedicated to study of a science or sciences and who…) in turmoil. According to astrophysicists, the two black holes from which the signal originated were about 30 times the mass of the Sun and located 1.5 billion light-years away.
Bringing theory and reality closer together
What mechanisms produce these black holes? Are they the product of the evolution of two stars, similar to our Sun but much more massive, evolving within a binary system? ? Or are they the result of black holes in densely populated star clusters meeting by chance? Could a more exotic mechanism be involved? These questions are hotly debated.
The POSYDON collaboration, which includes scientists from the universities of Geneva (UNIGE), Northwestern and Florida (UF) has made significant advances in the simulation of binary star populations. This work provides more precise answers and reconciles theoretical predictions and observational data. “Since it is impossible to directly observe the formation of binary black holes, it is necessary to rely on simulations that reproduce their observational properties. We do this by simulating binary star systems from their birth to the formation binary black hole systems”, explains Simone Bavera, post-doctoral fellow at the Department of Astronomy of the UNIGE Faculty of Sciences and main author of this study.
Pushing the boundaries of simulation
Interpreting the origins of merging binary black holes, like those observed in 2015, requires comparing the predictions of theoretical models with actual observations. The technique used to model these systems is known as “binary population synthesis”. It simulates the evolution of tens of millions of binary star systems in order to estimate the statistical properties of gravitational wave sources results.
“However, to achieve this in a reasonable timeframe, scientists have so far relied on models that use approximate methods to simulate the evolution of stars and their binary interactions. Thus, the oversimplification of star physics single and binary leads to less accurate predictions”, explains Anastasios Fragkos, assistant professor in the Department of Astronomy of the UNIGE Faculty of Science.
POSYDON made it possible to overcome these limitations. Designed as open source software, it uses a large pre-computed library of detailed single and binary star simulations to predict the evolution of isolated binary systems. Each of these detailed simulations can take up to 100 CPU hours to run on a supercomputer (A supercomputer (or supercomputer) is a computer designed to achieve the most…), which makes this simulation technique not directly applicable for binary population synthesis.
“However, by precomputing a library of simulations that span the entire initial condition space, POSYDON can use this dataset with machine learning methods to predict the full evolution of binary systems in less than a minute. second. This speed is comparable to previous-generation fast population synthesis codes, but with improved accuracy,” says Jeffrey Andrews, assistant professor in the UF Department of Physics.
Introduction of a new model
“Preceding POSYDON models predicted a negligible formation rate of merging binary black holes in galaxies similar to the Milky Way (The Milky Way (also called “our galaxy”, or sometimes…)), and they did not anticipate the existence of molten black holes as massive as 30 times the mass of our Sun. POSYDON has demonstrated that such black holes could exist in galaxies similar to ours”, explains Vicky Kalogera, professor in the Department of Physics and Northwestern Astronomy, Director of the Center for Interdisciplinary (Interdisciplinary work integrates concepts from different disciplines.) Astrophysics (from the Greek astro = star and physiqui = physics) is a branch…) (CIERA), and co-author of this study.
Previous models overestimated certain aspects, such as the expansion of massive stars. This led to an overestimation of their mass loss, which directly impacts binary interactions. These elements are key ingredients that determine the properties of molten black holes. Through fully self-consistent simulations of detailed stellar structure and binary interactions, POSYDON obtains more accurate predictions of the properties of molten binary black holes, such as their masses and spins.
This study is the first to use the POSYDON software. It brings new perspectives on the mechanisms of formation of black holes in fusion in galaxies like ours. The research team is currently developing a new version of POSYDON, which will include a larger library of detailed stellar simulations, capable of simulating binaries in a wider variety of galaxy types.
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