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How many black holes are there in the universe? 40,000,000,000,000,000,000

Large universe concept

With a new calculation method, SISSA researchers have been able to make the fascinating calculation. Moreover, according to their work, about 1% of the total common (baryonic) substance is trapped in star mass black holes.

How many black holes are there in the universe? This is one of the most relevant and pressing questions in modern astrophysics and cosmology. This intriguing issue has recently been addressed by SISSA Ph.D. student Alex Sicilia, supervised by Prof. Andrea Lapi and Dr. Lumen Boco, together with other partners from SISSA and from other national and international institutions. In the first paper in a series just released in The Astrophysical Journal, the authors have studied the demographics of stellar mass black holes, which are black holes with masses between a few to a few hundred solar masses that occurred at the end of massive star life.

"The innovative nature of this work lies in the coupling of a detailed model of stellar and binary evolution with advanced recipes for star formation and metal enrichment in individual galaxies. This is one of the first and one of the most robust ab initio. -calculations of the star black hole mass function across cosmic history. "- Alex Sicilia, first author of the study

According to new research, a remarkable amount of about 1% of the universe's total common (baryonic) matter is trapped in star mass black holes. Amazingly, scientists have found that the number of black holes in the observable universe (a sphere with a diameter of about 90 billion light-years) is currently about 40 billion billion (ie about 40 x 10 billion).18, i.e. 4 followed by 19 zeros!)

A new method of calculating the number of black holes

As the authors of the research explain: "This important result has been achieved thanks to an original approach that combines the advanced star and binary evolution code SEVN developed by SISSA scientist Dr. Mario Spera with empirical recipes for the properties of relevant physical galaxies, especially the rate of star formation, quantity of stellar mass and the metallicity of the interstellar medium (all of which are important elements in defining the number and masses of the star's black holes). By utilizing these crucial ingredients in a self-consistent approach, the black holes of the stars and their mass distribution throughout the history of the universe. Alex Sicilia, first author of the study, comments: "The innovative nature of this work is the coupling of a detailed model of stellar and binary evolution with advanced recipes for star formation and metal enrichment in individual galaxies. . This is one of the first and one of the most robust ab initio calculations of the mass function of the star's black hole throughout cosmic history. "

What is the origin of the most massive star-black holes?

The estimate of the number of black holes in the observable universe is not the only question that scientists have examined in this piece of research. In collaboration with Dr. Ugo Di Carlo and Prof. Michela Mapelli from the University of Padova, they have also explored the different formation channels for black holes with different masses, such as isolated stars, binary systems and star clusters. According to their work, the black holes of the most massive stars originate mainly from dynamic events in star clusters. Specifically, the researchers have shown that such events are necessary to explain the mass function of coalescing black holes as estimated from gravitational wave observations of LIGO/ Virgin cooperation.

Lumen Boco, co-author of the paper, comments: "Our work provides a robust theory for generating light seeds for (super) massive black holes at high redshift and can provide a starting point for investigating the origin of 'heavy seeds'', which we will pursue in a forthcoming paper.

An interdisciplinary work carried out in connection with "BiD4BESt - Big Data Application for Black Hole Evolution Studies"

Prof. Andrea Lapi, Sicily's supervisor and coordinator of Ph.D. in astrophysics and cosmology at SISSA, adds: "This research is truly multidisciplinary and covers aspects of and requires expertise in stellar astrophysics, galaxy formation and evolution, gravitational waves and multi-messenger astrophysics; as such it requires collaborative efforts from various members of SISSA The Astrophysics and Cosmology Group and a strong network of external partners. "

Alex Sicilia's work takes place in connection with a prestigious Innovative Training Network Project "BiD4BESt - Big Data Application for Black Hole Evolution Studies" co-PIeret by Prof. Andrea Lapi from SISSA (H2020-MSCAITN-2019 Project 860744), which has been funded by the European Union with around € 3.5 million in total; it involves several academic and industrial partners to provide Ph.D. training for 13 early researchers in the formation of black holes and evolution by utilizing advanced computer science techniques.

Reference: "The Black Hole Mass Function Across the 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

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