Scientists estimate the number of black holes in the universe. It's a lot.
spotting black holes is not the easiest task, so it might seem impossible to calculate this number. The light swallowing Cosmic goliaths can only be seen under the most extraordinary circumstances, like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling.
Scientists are still finding ways to guess the number. A new method for estimating the number of stellar-mass black holes in the universe was outlined in The Astrophysical Journal.
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According to the new estimate, 40,000,000,000,000,000,000, or 40 quintillion, stellar-mass black holes make up approximately 1% of all normal matter.
How did the scientists arrive at that number? Alex Sicilia, an astronomer at the International School of Advanced Studies (SISA) in Trieste, Italy, said that they estimated how often stars would transform into black holes by tracking the evolution of stars in our universe.
"This is one of the first, and one of the most robust, computations of the stellar black hole mass function across the history of the universe," Sicilia said in a statement.
To make a black hole, you need a star with a mass five to 10 times that of the sun. As big stars reach the end of their lives, they begin to add heavier elements to their fiery cores. The star is on a path to violent self-destruction once the fusion process begins. The star loses its ability to push out against the enormous force of its mass when iron takes in more energy than it gives out. It collapses in on itself, packing first its core and then all the matter close to it, into a point of infinitesimal dimensions and infinite density. The star becomes a black hole, and beyond a boundary called the event horizon, nothing can escape its pull.
The pre-lives of the universe's stars were modeled by the astrophysicists to arrive at their estimate. The team built a model of the universe that accurately reflected the different sizes of stars that would be made, and how often they would be created.
After pinning down the rate of formation for stars that could eventually transform into black holes, the researchers modeled the lives and deaths of those stars using data such as their mass and metallicity. The researchers made sure that they didn't double-count any black holes in their survey by looking at stars and calculating the rate at which black holes can meet each other. They figured out how the mergers and snacking by black holes on nearby gas would affect the size of the universe.
The model the researchers designed tracked the population and size distribution of stellar-mass black holes over time to give them their eye-watering number. The researchers confirmed that their model was in agreement with the data when they compared it to the estimate.
Astrophysicists hope to use the new estimate to investigate some questions that arise from observations of the very early universe, such as how the early universe became so quickly populated by supermassive black holes, often with millions, or even billions, of times greater than the stellar-mass holes.
The researchers hope that a better understanding of how small black holes formed in the early universe could help them to discover the origins of their supermassive cousins.
"Our work provides a robust theory for the generation of light seeds for supermassive black holes at high redshift, and can constitute a starting point to investigate the origin of "heavy seeds", that we will pursue in a forthcoming paper," said Lumen Boco.
It was originally published on Live Science.
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