How many black holes are out there in the universe?

The number of black holes in the observable Universe (a sphere with a diameter of about 90 billion light years) is currently about 40 trillion, that is, 40 followed by 18 zeros. It is the figure obtained from a new computational approach to calculate the number of black holes, presented in The Astrophysical Journal.

The research has been undertaken by SISSA (Scuola Internazionale Superiore di Studi Avanzati) doctoral student Alex Sicilia, supervised by Professor Andrea Lapi and Dr. Lumen Boco, together with other collaborators from this Italian center and from other national and international institutions. .

The authors investigated the demographics of stellar-mass black holes, which are black holes with masses between a few and hundreds of solar masses, that originated at the end of the lives of massive stars.

“This important result has been obtained thanks to an original approach that combines the state-of-the-art stellar and binary evolution SEVN code developed by SISSA researcher Dr. Mario Spera with empirical prescriptions for relevant physical studies. 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 masses of stellar black holes)”, reports SISSA in a release.

Alex Sicilia, first author of the study, comments: “The innovative character 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 most robust ab initio calculations of the stellar black hole mass function throughout cosmic history.”

Also, according to the new research, a remarkable amount of about 1% of the overall ordinary (baryonic) matter in the Universe is locked up in stellar-mass black holes.

Estimating the number of black holes in the observable Universe is not the only topic investigated by scientists in this research. In collaboration with Dr. Ugo Di Carlo and Professor Michela Mapelli from the University of Padua, they also explored the various formation channels of black holes of different masses, such as single stars, binary systems and star clusters.

According to their work, the most massive stellar black holes originate mainly from dynamical 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 the LIGO/Virgo collaboration gravitational-wave observations.

A super massive black hole

A team led by the Andalusian Institute of Astrophysics (IAA-CSIC), has observed the central regions of the galaxy OJ 287, revealing the existence of a unique duo of black holes.

Analysis of the data revealed that this spectacular source exhibits a highly curved plasma jet containing several knots, or brighter regions, the nature of which is unknown. Comparison of space-based and ground-based observations revealed a progressive curvature of the jet with increasing angular resolution, consistent with theoretical predictions that OJ 287 harbors not one, but two supermassive black holes, with the secondary orbiting the primary and piercing its surface. accretion disk twice every 12 years.

In addition, the team found that, while the energy in the innermost regions of the jet arises from the plasma particles, at greater distances it comes from both the particles and the local magnetic field. They also found evidence that the magnetic field, in the innermost regions, is coiled into a helical structure that is consistent with models of jet formation.

The discovery has been possible thanks to the technique known as very long-baseline interferometry (VLBI), which allows multiple geographically separated radio telescopes to work in unison, functioning as a telescope with a diameter equivalent to the maximum distance that separates them.

In this case, the science team observed OJ 287 with antennas on the ground and in space. The participation of the antenna in orbit of ten meters Spektr-R (RadioAstron mission, of the Moscow Astro Space Center and supported by the Russian Space Agency), allowed to create a radio telescope with a diameter 15 times greater than that of the Earth. The resulting image is equivalent to distinguishing, from the ground, a 20-cent coin on the surface of the Moon. “We have never looked at the inner workings of the jet in OJ287 in such fine detail,” Traianou notes.