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Study Investigates the Demographics of Stellar Mass Black Holes

The existence of the number of black holes in the Universe has been considered the most appropriate and pressing question in the field of modern astrophysics and cosmology.

Study Investigates the Demographics of Stellar Mass Black Holes.

Image Credit: International School for Advanced Studies.

The interesting problem has recently been discussed by the International School for Advanced Studies (SISSA) Ph.D. student Alex Sicilia. It was monitored by Professor Andrea Lapi and Dr. Lumen Boco, collectively with other collaborators from SISSA and from other national and international institutions.

In the first paper of a series recently reported in The Astrophysical Journal, the authors have analyzed the demographics of stellar mass black holes, which are known as black holes having masses between a few to some hundred solar masses. They originate from the end of the life of massive stars.

As per the new study, a notable amount of around 1% of the overall ordinary (baryonic) matter of the Universe has been closed in stellar mass black holes.

Surprisingly, the scientists have discovered that various black holes inside the observable Universe (a sphere of diameter around 90 billion light years) at present time is nearly 40 trillions, 40 billion billions (that is., nearly 40 × 1018, that is, 4 followed by 19 zeros).

A New Method to Calculate the Number of Black Holes

As the authors of the research explain, “This important result has been obtained thanks to an original approach which combines the state-of-the-art stellar and binary evolution code SEVN developed by SISSA researcher Dr. Mario Spera to empirical prescriptions for relevant physical properties of galaxies, especially the rate of star formation, the amount of stellar mass and the metallicity of the interstellar medium (which are all important elements to define the number and the masses of stellar black holes).

Utilizing these vital ingredients in a self-consistent approach along with the novel computation approach, the scientists later derived the number of stellar black holes and their mass distribution across the whole history of the Universe.

The innovative character of this work is 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 computation of the stellar black hole mass function across cosmic history.

Alex Sicilia, Study First Author, International School for Advanced Studies

What is the Origin of Most Massive Stellar Black Holes?

The evaluation of the various black holes in the observable Universe is not the only problem that has been examined by the researchers in this study.

Jointly with Dr. Ugo Di Carlo and Professor Michela Mapelli from the University of Padova, they have also discovered various formation channels for black holes of different masses, including isolated stars, stellar clusters and binary systems. As per their work, the enormous stellar black holes originate primarily from dynamic events in stellar clusters.

Particularly, the scientists have displayed that there is a necessity for such events to describe the mass function of coalescing black holes as estimated from gravitational wave observations made by the LIGO/Virgo collaboration.

Our work provides a robust theory for the generation of light seeds for (super)massive black holes at high redshift, and can constitute a starting point to investigate the origin of ‘heavy seeds’.

Lumen Boco, Study Co-Author, International School for Advanced Studies

A Multidisciplinary Work Carried Out in the Context of “BiD4BESt — Big Data Application for Black Hole Evolution studies”

This research is really multidisciplinary, covering aspects of, and requiring expertise in stellar astrophysics, galaxy formation and evolution, gravitational wave and multi- messenger astrophysics; as such it needs collaborative efforts from various members of the SISSA Astrophysics and Cosmology group, and a strong networking with external collaborators.

Andrea Lapi, Professor, International School for Advanced Studies

Andrea Lapi is also a supervisor and coordinator of the Ph.D. in Astrophysics and Cosmology at SISSA.

Alex Sicilia’s work comes in the context of a renowned Innovative Training Network Project entitled, “BiD4BESt — Big Data Application for Black Hole Evolution Studies” and co-PIed by Professor Andrea Lapi from SISSA (H2020-MSCAITN-2019 Project 860744).

The study has been financially supported by the European Union with nearly 3.5 million Euros overall; it involves various academic and industrial collaborators, to offer Ph.D. training to 13 early-stage scientists in the area of black hole formation and evolution, by using up the latest data science methods.

Journal Reference:

Silica, A., et al. (2022) The Black Hole Mass Function Across Cosmic Times. I. Stellar Black Holes and Light Seed Distribution. The Astrophysical Journal.

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