How many black holes are there in the universe? The latest number: 400 billion billion!

How many black holes are there in the universe? This is one of the most pressing questions in modern astrophysics and cosmology, and scientists have finally given the answer!

Scientists from the International School for Advanced Studies (SISSA) in Italy and other institutions wrote in the latest issue of "The Astrophysical Journal" that they have counted the number of stellar black holes for the first time and calculated their distribution throughout the universe. Based on this, they calculated that the number of black holes in the currently observable universe is about 400 trillion.

Image source: Tuchong Creative

In the latest study, scientists have integrated the most advanced stellar and binary evolution algorithm SEVN developed by SISSA researcher Dr. Mario Spera with empirical formulas for galaxy-related physical properties (especially the star formation rate, the number of stellar-mass black holes, and the metallic content of the interstellar medium), and developed a unique calculation method to reach the above conclusions.

Stellar-mass black holes have masses ranging from a few to hundreds of solar masses and originate from the end of the life of massive stars. New research indicates that about 1% of ordinary matter in the universe is "locked" in stellar-mass black holes.

The researchers explained: "Properties such as the rate of star formation are important elements in defining the number and mass of stellar black holes. With the help of new calculation methods, we have obtained the number of stellar black holes and their mass distribution throughout the history of the universe, and based on this, we have obtained the number of black holes in the entire observable universe."

Dr Alex Cecilia, lead author of the study, commented: "This is the first time scientists have calculated the number of stellar-mass black holes, and the conclusions they have drawn are the most robust yet."

This research covers various aspects of stellar astrophysics, galaxy formation and evolution, gravitational waves and multi-messenger astrophysics, and lays a solid foundation for further research on stellar-mass black holes and their origins.”

You can also learn about black holes

Black holes can absorb even light, so they themselves are invisible, but we can see the luminous matter around them, which can be brighter than the sum of all the stars in their host galaxy.

The formation of black holes is closely related to the collapse of stars. There is a record in ancient China that one day a particularly bright star suddenly appeared in the sky. Later we learned that the star collapsed under its own gravity because it was overweight, accompanied by strong radiation, so we saw the bright light it emitted.

In 1783, British geologist and astronomer John Michell discovered while studying Newton's gravity: when the density of a celestial body is large enough, its gravity will be extremely strong and all matter close to it will be attracted in.

In 1915, Einstein proposed the theory of general relativity. A few months later, Schwarzschild, who was on the battlefield in Germany, obtained the exact solution of Einstein's field equations after making a spherical approximation to the field equations. This solution reflects a non-rotating black hole, which is the Schwarzschild black hole we know today. In the real universe we know, almost all celestial bodies have angular momentum and are in a state of rotation, so people do not believe that the non-rotating solution obtained by Schwarzschild really exists.

In the following decades, due to the constant war, relevant astronomical observations were very scarce. In terms of theory, Oppenheimer and his students made the only discovery in the late 1930s: when a massive star finally dies, if it collapses spherically, it will eventually form a singularity, which is what we call a black hole.

In 1979, scholar Jean-Pierre Luminet used computer calculations and hand-painted the first black hole rendering.

From then on, human imagination of black holes entered the visual stage.

The first black hole rendering

In 1989, Jean-Alain Marck used computers to simulate black holes from various angles. They looked like flying saucers or lanterns looking down.

Simulating a black hole

After 2000, with the advancement of science and technology, scientists simulated the distorted image of a galaxy passing through a black hole. In 2014, director Nolan even gave the most "real" black hole image in the science fiction film "Interstellar".

Black hole in the movie Interstellar

In 2015, humans detected gravitational waves for the first time, providing the first concrete evidence for the existence of black holes. Scientists described it as the first time humans "heard" a black hole.

On April 10, 2019, the Event Horizon Telescope (EHT) collaboration coordinated a global collaboration to release the first photo of a black hole. This has since verified Einstein's theory of general relativity from the perspective of a strong gravitational field.

The first black hole photo taken by humans is an image of the supermassive black hole (M87*) at the center of the M87 galaxy. The dark area in the center of the photo is the "black hole shadow", and the surrounding annular asymmetric structure is caused by the strong gravitational lens effect and the relativistic beaming effect. Due to the rotation effect of the black hole, the image shows an asymmetry between the top (north) and the bottom (south).

What is the significance of black hole research to the development of science?

For scientists, the study of black holes not only helps us better understand the natural laws of celestial evolution, but more importantly, it helps us understand the relationship between quantum mechanics and gravitational theory and the role of black holes in the evolution of the universe.

What is known so far is that there is still time and space inside a black hole. It is possible that black holes are truly immortal and will grow bigger and fatter. So what will happen if a person "falls" into a black hole? Will he fall into the central singularity of the black hole? Hopefully, one day, scientists can give us the answer.

Comprehensive sources: Science and Technology Daily, Institute of High Energy Physics, Chinese Academy of Sciences, Xinhuanet, China Science Expo, etc.