How Many Black Holes Are There In Total? How Do We Estimate This Number?

Black holes are older than many objects in the universe and their number is simply colossal. Their origin and formation tells about our past and future.

Stephen Hawking would be so delighted to see the growing interest and advancement in the field of Science pertaining to black holes. It was his dream and vision to be able to not just understand the entirety of a black hole’s functioning and also view it in all its glory.

After all, his role in redefining pre-existing assumptions and solidifying mere guesswork surrounding black holes is pivotal in taking the human race to where we are today. The term black hole might trigger a series of thoughts in your mind that make you think of it as something deadly and potentially catastrophic but its true beauty and sheer might are still uncharted. Let’s try and map out some portion of this otherwise extensive area of the cosmos.

supernova

A supernova (Photo Credit : Pixabay)

What is a black hole?

Just about the only thing that sci-fi movies have got right over the years is the meaning of a black hole. A black hole  typically refers to an area in space where the gravitational force is so ginormous that no matter or radiation can escape it. Even light can’t break this cycle which amounts to us being unable to see them.

The most common cause behind the birth of a black hole is the death of a star. So while it is impossible to see black holes, very advanced telescopes are used to observe the structure and behaviour of stars that are thought of being close to one owing to the fact that they behave differently when in vicinity of this ‘Cosmic titan’.

Constituents of a black hole

  • Inner and outer event horizons – The boundary of the black hole beyond which we the mass disappears. Can be thought of as the last pit stop before one individual entities become one mass. Concept proposed by John Michell and term coined by Wolfgang Rindler.
  • Singularity – The singularity of a black hole is that one point in space and time where the entire mass  of the black hole is concentrated. The meaning of individual entities is lost at this point. Discovered by Ezra Newman.

cosmic rays, prostar

Black hole with event horizon and nebula (Photo Credit : Wikimedia Commons)

How do black holes form and what is their range of size?

While most scientists argue that the first black holes emerged when the universe initially started expanding, its the ‘Stellar’ black holes that are formed when the core of an extremely big star collapses on itself. But, supermassive black holes are thought to have come into existence at the very same time as the galaxies they are part of.

The one thing that is common to most if not all black holes is the path they take after the parent star has died. When the fuel of the star reaches its end, the first process that takes place is the conversion of hydrogen to helium followed by the further burning of helium once the hydrogen runs out too.

The wide array of sizes of black holes is insane to the say the least!! Some black holes (micro black holes) are as tiny as an atom while some are so big, they can engulf entire galaxies in a single go and capable of holding around 1 million suns together.

An artist's depiction of a black hole in interstellar space pulling in gas and dust that start to heat(Marc Ward)s

Singularity of a black hole being visualised (Photo Credit : Marc Ward/Shutterstock)

How do we locate black holes??

This question at first seems absurd because one would say “even light doesn’t escape a black then how can we locate one” but on closer look into the characteristics of black holes, there are a few ways in which they can be remotely and precisely located.

  • The first method is to pay close attention to the gravitational aspects of a black hole. Any black hole would cause the neighbouring entities to come closer to it and cluster around it, ultimately falling into the dense one way path. As simple as this method sounds, it is not very practical because of it depending a lot on chance. It is a hit and trial method since numerous other phenomena also cause a similar effect on stars and planets.
  • The second method includes looking out for possible X-ray emissions. When matter falls into the black hole, it gets collected in a dense ring like structure, just at the horizon and the unparalleled energy is converted to light on some occasions, making it feasible to locate a one of these big boys.

How many black holes are there?

The density of black holes varies over a wide range of properties of space like the type of galaxy, type of stars found in it etc. To estimate the number of black holes in a certain galaxy, the dust and gas formations need to be keenly observed. The behaviour of two nearby black holes is affected greatly by the gravitational pull of the other. This very fact puts a limit on the closeness two black holes can have.

In just the observable universe, the extent to which we can perceive it, there are some 100 trillion black holes. While this number is huge, only 100-200 of these have actually been discovered after pin pointing their exact location.

Supermassive black holes and quasers like 1ES 2344+514 and Fornax A exist while intermediate black holes like HLX-1 and stellar black holes like GX 339-4/V821 Ara have also been discovered.

In addition to this, there is something known as black hole systems that point to more than one black hole in close vicinity. These systems have distinctive properties which either stem from the properties of the largest black hole in the system or are a culmination of all.

How do we estimate the number of black holes?

The first step towards finding the approximate number of black holes in the universe is segregating areas according to certain characteristics such as closeness to a galaxy, star etc. On observing the same set of attributes and applying them to different points of the same area, an average number of black holes comes up with 10-20 holes as buffer.

The next step is to find similarities between the multiple key areas and categorise the black holes as supernova, quasers etc. Because each type pf black hole entity has very polar characteristics, it is somewhat possible to locate more of the same type in a range bounded area.

The scope of research about black holes is ceaseless. It would take more then a lifetime to comprehend them in all their glory but what remains a difficult venture to undertake could also tell us so much more about our future and past. Only time would tell whether the fiction portrayed in movies like Interstellar and The Arrival could be factual!

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About the Author

Seerat Gill is currently pursuing Computer Science Engineering from Chitkara University, Punjab. In her free time, she loves to read novels and write about topics on varied levels of the spectrum. Being a space travel enthusiast, she loves to read up on articles pertaining to futuristic approaches to space travel in the time to come.

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