Around 1% of the ordinary (baryonic) matter in the universe is trapped in stellar-mass black holes, according to the estimate made by a team of Italian and English astrophysicists from the International School for Advanced Studies (SISSA) who have calculated how many black holes can be in a sphere of about 90,000 million light years in diameter , that is, the observable universe.
The figure is about 40 trillion (40 million million million, or a “4” followed by 19 zeroes). This finding paves the way for a better understanding of how stellar and intermediate-mass black holes might evolve into supermassive black holes, say the authors, whose study is published in The Astrophysical Journal.
What is a stellar-mass black hole?
Stellar-mass black holes are those that form at the end of the lives of giant stars and have masses between a few and a few hundred times that of the sun (range 5-150 solar masses). Supermassive black holes are in the range of 105-110 solar masses. The group of intermediate-mass black holes is the most confusing, as only tentative evidence for them has been identified. They are in the range of 103-106 solar masses.
“One of the most fundamental quantities for demographic studies of the population of black holes is constituted by the relic mass function, that is, the number density of black holes per comoving volume and unit mass of black hole, as a function of the displacement to the red ”, exposes Alex Sicilia of the Scuola Internazionale Superiore di Studi Avanzati.
a new method
The researchers used a new method that combines the state-of-the-art stellar and binary evolution SEVN code developed by SISSA researcher Mario Spera with empirical prescriptions for relevant physical studies, such as the properties of galaxies, especially the rate of galaxy formation. stars.
“We provide an estimate of the stellar black hole relic mass function over cosmic times, by coupling the latest-generation stellar and binary evolutionary code SEVN to redshift-dependent galaxy statistics and empirical relationships. of scale that involve metallicity, star formation, speed and stellar mass”, the experts continue.
Thanks to this new computational approach, they were able to determine the number of stellar black holes and their mass distribution throughout the history of the universe. “This is one of the first and most robust ab initio calculations of the stellar black hole mass function throughout cosmic history,” they explain in their paper.
They found that the largest stellar-mass black holes typically form from the collision of smaller black holes within star clusters, a notion that agrees well with the gravitational-wave observational data on black hole collisions collected to date.
This is an important milestone in astrophysics, since it could help us determine the number of black holes that should be in any volume of space that we consider; which, in turn, would provide substantial information on the growth and evolution of the holes that make up the nuclei of galaxies, supermassive black holes.
This work has been the first of a series. The following will investigate intermediate-mass black holes and supermassive black holes to get a more complete picture of the distribution of black holes throughout the universe.
Referencia: “The Black Hole Mass Function Across Cosmic Times. I. Stellar Black Holes and Light Seed Distribution” by Alex Sicilia, Andrea Lapi, Lumen Boco, Mario Spera, Ugo N. Di Carlo, Michela Mapelli, Francesco Shankar, David M. Alexander, Alessandro Bressan and Luigi Danese, 12 January 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac34fb
