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What is the total number of black holes in the universe?


A recent research looked at stellar mass black holes, which are black holes with masses ranging from a few to hundreds of solar masses that formed near the conclusion of huge stars’ lives. According to the findings, star mass black holes hold a tremendous quantity of stuff, accounting for around 1% of the universe’s total ordinary matter. Surprisingly, the researchers discovered that the current number of black holes in the visible universe is about 40 times 10 to the exponent 18.

What is the total number of black holes in the universe?

This is one of the most important and serious issues in current cosmology and astrophysics-

The fascinating problem was recently addressed by SISSA Ph.D. student Alex Sicilia, who was supervised by Prof. Andrea Lapi and Dr. Lumen Boco, as well as other SISSA and national and international colleagues. The scientists explored the demography of stellar mass black holes, which are black holes with masses ranging from a few to a few hundred solar masses that formed near the end of the lives of huge stars, in the first of a series of papers just published in The Astrophysical Journal. According to the latest findings, star mass black holes hold a significant portion of the Universe’s total ordinary (baryonic) stuff, roughly 1%. Surprisingly, the researchers discovered that the current number of black holes in the visible Universe is about 40 x 1018 (that’s four followed by 19 zeros!).

A novel approach for calculating the number of black holes has been developed

According to the research’s authors: “This significant result was achieved thanks to a novel approach that combines the state-of-the-art stellar and binary evolution code SEVN developed by SISSA researcher Dr. Mario Spera with empirical prescriptions for important physical properties of galaxies, particularly the rate of star formation, stellar mass, and interstellar medium metallicity (which are all important elements to define the number and the masses of stellar black holes). The researchers used their innovative computing technique to determine the number of star black holes and their mass distribution over the whole history of the Universe by combining these critical elements in a self-consistent manner. The study’s primary author, Alex Sicilia, had this to say: “The combination of a thorough model of stellar and binary development with sophisticated recipes for star formation and metal enrichment in specific galaxies is what makes our work unique. This is one of the earliest ab initio computations of the stellar black hole mass function in cosmic history, as well as one of the most reliable.”

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The origin of the vast majority of big stellar black holes

The quantity of black holes in the visible Universe isn’t the only problem that the researchers are looking at in their study. They’ve also looked at the many formation routes for black holes of various masses, such as single stars, binary systems, and stellar clusters, in partnership with Dr. Ugo Di Carlo and Prof. Michela Mapelli from the University of Padova. The most massive stellar black holes, according to their findings, are created mostly by dynamical processes in star clusters. The researchers have shown that such occurrences are necessary to explain the mass function of merging black holes as determined by the LIGO/Virgo collaboration using gravitational wave measurements.

Lumen Boco, one of the report’s co-authors, says: “Our findings give a solid foundation for the formation of light seeds for (super)massive black holes at high redshift, and may serve as a springboard for further research into the genesis of ‘heavy seeds,’ which we will explore in a future publication.

“This research is truly multidisciplinary, covering aspects of, and requiring expertise in stellar astrophysics, galaxy formation and evolution, gravitational wave and multi-messenger astrophysics; as such, it requires collaborative efforts from various members of the SISSA Astrophysics and Cosmology group, as well as strong networking with external collaborators,” says Prof. Andrea Lapi, Sicilia’s supervisor and coordinator of the Ph.D. in Astrophysics and Cosmology at SISSA.

Alex Sicilia’s work is part of the Innovative Training Network Project “BiD4BESt — Big Data Application for Black Hole Evolution Studies,” which is co-PIed by Prof. Andrea Lapi of SISSA (H2020-MSCAITN-2019 Project 860744) and is funded by the European Union with approximately 3.5 million Euros in total. It involves several academic and industrial partners, and aims to provide Ph.D. training to 13 early stage researchers in the area of black hole formation

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