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Space: about 40,000,000,000,000,000 black holes make up 1% of the observable universe

Have you ever wondered how many black holes there are? About 40,000,000,000,000,000,000,000,000 make up 1% of the observable universe, study estimates

  • This calculation comes from the International School for Advanced Studies, Italy
  • They took into account data on properties such as stellar evolution and formation rates
  • The finding could help us better understand the evolution of supermassive holes



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The observable universe contains 40,000,000,000,000,000,000,000 black holes of stellar mass — that’s 40 trillion, or 40 billion billions, a study estimates.

Stellar-mass black holes are those that form at the end of the life of giant stars and have masses between a few and a few hundred times that of the Sun.

Experts from the International School for Advanced Studies (SISSA) used a new computational approach to estimate how many of these holes should have formed.

In addition, they said, these black holes account for 1 percent of all ordinary or “baryonic” matter in the observable universe, which is 93 billion light-years across.

The findings, the team said, pave the way for a better understanding of how stellar and intermediate black holes might evolve into supermassive black holes.

The observable universe contains 40,000,000,000,000,000,000,000 black holes of stellar mass — that's 40 trillion, or 40 billion billions, a study estimates.  Pictured: A simulated image of a black hole in front of the Large Magellanic Cloud

The observable universe contains 40,000,000,000,000,000,000,000 black holes of stellar mass — that’s 40 trillion, or 40 billion billions, a study estimates. Pictured: A simulated image of a black hole in front of the Large Magellanic Cloud

THE ‘OBSERVABLE UNIVERSE’

In their study, astrophysicist Alex Sicilia and colleagues calculated the number of stellar-mass black holes in the entire universe — not the “observable” part.

This is the spherical region, centered on Earth, bounded by the furthest distances we could possibly see with our ground and space telescopes, given the speed of light and the amount of time that has passed since the cosmological expansion.

Beyond this boundary – also called the ‘particle horizon’ – nothing can be detected. The observable universe is currently about 93 billion light-years across.

The calculation was performed by theoretical astrophysicist Alex Sicilia of Trieste, Italy-based SISSA and his colleagues.

‘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,’ explains Mr. Sicilia.

‘This is one of the first and one of the most robust ‘ab initio’ [from first principles] calculation of the mass function of the stellar black hole in cosmic history.’

To calculate their estimate of the number of black holes in the observable Universe, the team combined models of how single and binary star pairs evolve — and thus how many black holes become — with data on other relevant galactic properties.

The latter contained information about star formation rates, the masses of stars and the metallicity of the interstellar medium – all of which influence the formation of stellar black holes. They also took into account the role of black hole mergers.

From this, the team was also able to calculate the mass-mass distribution of these black holes over the entire history of the observable universe.

In addition to estimating the total number of stellar black holes in the observable universe, the researchers also investigated different routes through which black holes of different masses can form.

This included looking for possible origins in isolated stars, binary star systems and more densely populated stellar clusters.

The team found that the largest stellar-mass black holes usually form from the collision of smaller black holes in stellar clusters — an idea that agrees well with the observational gravitational wave data collected so far on black hole collisions.

‘Our work provides a robust theory for light generation’ [stellar-mass] seeds for (super)massive black holes with a high redshift’, says author and astrophysicist Lumen Boco, also of SISSA.

Such, he added, “could provide a starting point to investigate the origin of ‘heavy seeds'” [intermediate-mass black holes], which we will pursue in a future paper.’

Now that this initial study has been completed, the researchers now want to perform similar calculations, focusing instead on medium-mass black holes and then on their supermassive counterparts.

The full findings of the study were published in The Astrophysical Journal.

BLACK HOLES HAVE A GRAVITY SO STRONG EVEN LIGHT CAN’T ESCAPE

Black holes are so dense and their gravitational pull so strong that no form of radiation can escape them – not even light.

They act as intense sources of gravity that suck up dust and gas around them. Their intense gravitational pull is believed to be what stars in galaxies revolve around.

How they are formed is still poorly understood. Astronomers think they could form when a large cloud of gas up to 100,000 times larger than the Sun collapses into a black hole.

Many of these black hole seeds then coalesce to form much larger supermassive black holes, found at the center of every known massive galaxy.

Alternatively, a supermassive black hole seed could come from a giant star, about 100 times the mass of the sun, which eventually forms into a black hole after it runs out of fuel and collapses.

When these giant stars die, they also go “supernova,” a massive explosion that expels matter from the star’s outer layers into deep space.

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