:: OSEL.CZ :: – How many star-sized black holes are there in the universe?

Calculating black holes is not easy at all. They are not visible. But astrophysicists usually have other options. Based on models and observed data, the Italian team estimates that we have about 40 trillion black holes of stellar origin in the observable universe. They should contain about 1 percent of the normal mass of the universe.

How many black holes are there? Credit: Alain r / Wikimedia Commons.

As everyone knows, black holes are black, and you wouldn’t normally see it, even if you had it in front of your nose. Yet astrophysicists are very interested in how many black holes there are in space. The answer to this question actually represents the demographics of black holes created by the collapse of massive stars. This results in their maximum mass, which is a maximum of a few hundred Suns.

Logo.  Credit: SISSA.

Logo. Credit: SISSA.

Alex Scilla of the Italian SISSA Institute (Scuola Internazionale Superiore di Studi Avanzati) and his colleagues embarked on the “counting” of such black holes. Their calculations show that in the observable universe, a sphere about 90 billion light-years across, there are about 40 billion billion, or 40 trillion (ten to eighteen) star-sized black holes. They also show that these black holes contain about 1 percent of all baryon, that is, ordinary, non-dark matter in the universe.

The researchers combined advanced SEVN star and binary evolution models with relevant galaxy physical properties, including star-forming velocity, star mass, and interstellar metallicity.

The largest stellar black holes form in star clusters.  Credit: NASA, ESA / Wikimedia Commons.

The largest stellar black holes form in star clusters. Credit: NASA, ESA / Wikimedia Commons.

From these ingredients, they derived the number of black holes and the distribution of their mass throughout the history of the universe.

Scilla and colleagues also studied different trajectories of the evolution of black holes of different masses, such as the formation of solitary stars, the formation in binary systems, or the formation in star clusters. They have found that the largest black holes of stellar origin typically arise during star cluster events.

Scientists believe that such events can explain the existence of black holes of unexpected sizes, whose collisions have detected gravity observatories and with which we do not know much.


SISSA 18. 1. 2022.

Astrophysical Journal 924: 56.

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