Black holes are where God divided by zero.
블랙홀은 신이 0으로 나눈 곳입니다.
Comedian Steven Wright (and not Albert Einstein) once famously said that Black holes are where God divided by zero. What other title would have been best to describe these weird regions in space other than this one? Anyway, there are several mysterious objects in this universe that we haven't been able to understand so far. Black holes are one of them. For anyone who has no idea what black holes are, there are certain objects in space where gravitational attraction is so massive that nothing can escape from them, not even light. Such objects are called black holes. What we have known and understood so far about them is how they are formed, what are they made of, and how to detect them in space. But we do not exactly know what’s inside a black hole. Practically it’s nearly impossible to know so because even if we send a probe or a spacecraft inside a black hole, it won’t be able to come out of the influence of it, and nor will it be able to send us any signal from in there. So far, whatever predictions we have made about black holes are all theoretical. In this story, I shall share some fascinating facts about black holes and the science associated with them.
Black holes are not visible to us because the gravitational influence in the region is significantly high for photons to escape. They are formed as a result of stellar evolution when all the matter of stars is compressed to a small region of space. This happens when the mass of the remnant of a supernova is significantly greater than the solar masses.
Every matter can potentially create a black hole. This might sound like a crazy hypothesis but it is true. Let me explain. We know that every matter has a specific mass. If we could somehow compress the mass of the object within its Schwarzschild radius. Every object has a different Schwarzchild radius and it can be calculated by using a simple mathematical formula.
In the above formula,
G= Universal gravitational constant
M= Mass of the object
c= Speed of light in vacuum
For larger stellar masses, the Schwarzchild radius is significantly higher which makes it possible for them to compress their masses within the radius forming a singularity with infinite density. The infinite dense gravitational singularity results in the extreme gravitational influence. The concept of singularity is not a physical object. It’s an infinitesimally small mathematical dot.
The sizes of black holes differ according to their masses. They can, however, be divided into three major types. The first kind is called a primordial black hole. Such black holes are as small as the size of an atom. Cosmologists believe that the formation of primordial black holes took place during the early universe after the big bang. These black holes are as small as atoms but their masses are extremely high. The black holes that are most abundant and detectable are medium-sized or intermediate-sized black holes or stellar black holes. The masses of stellar black holes are nearly twenty times the mass of our sun. But mass gets compressed within the radius of the Schwarzchild sphere and their diameter is nearly 10 miles. Some black holes are insanely huge in size. They’re called supermassive black holes. The mass of a supermassive black hole is more than a million solar masses. But its mass is compressed to a relativity smaller size about as big as our solar system. Scientific observations prove that almost every galactic centers have supermassive black holes. Even our milky way has a central supermassive black hole called the Sagittarius A*. Recently an image of Sgr A* was released worldwide by the Event Horizon Telescope collaboration. I have already written a piece on this topic that you can read here:
There is a common myth about black holes that exist amongst the common non-scientific populace that black holes suck everything in even from large distances which aren’t true. Until and unless the object comes significantly close to a black hole, it cannot take the object in. If you have watched the movie Interstellar, then you must have noticed one planet named Miller that revolves around a massive black hole named Gargantua. Even if our sun somehow turns into a black hole, it shall not consume all the revolving planets. But of course, our sun isn't massive enough to form a black hole. After a few billion years, the sun will convert itself into a red giant and when all of its fuel will end, it will become a planetary nebula ending its fate with a white dwarf.
One of the greatest mysteries about black holes is that we do not exactly know what happens inside them. Current theories predict that all the matter consumed by a black hole gets squeezed into the infinitesimally small gravitational singularity. But we do not yet understand how these singularities work. Singularities are those regions in space where gravitational force gets reconciled with quantum mechanical phenomena and hence they require a quantum theory of gravity for a clear understanding. I have written a separate piece about the breaking down of laws of physics in spacetime singularities:
Some speculations predict that black holes function as potential wormholes in the universe. Wormholes are also known as Einstein-Rosen bridges and they are basically space-time shortcuts formed due to the immense warping of the space-time continuum. Wormholes were the predictions of the solutions of Einstein’s field equation from his general theory of relativity. Since we do not have any observational or experimental evidence of the existence of wormholes, they are only a matter of purely mathematical speculation so far. Even if somehow one could get inside a black hole, it would be impossible to survive near the singularity. As you approach the singularity of a black hole, your body would stretch to a great extent, including the molecules that make up your body. Such phenomenon caused due to the powerful gravitational influence of black holes is known as Spaghettification. Sounds like a fascinating food processing term but it is a deadly universal phenomenon.
Gargantua, the black hole as depicted in the 2014 Sci-fi film by Christopher Nolan, Interstellar. Image source and credit: Interstellar
According to the late Stephen Hawking, black holes do not always consume matter but they also emit a kind of radiation over time known as Hawking radiation. Such radiation evaporating process causes black holes to lose their energy and masses. The black holes that do not have any matter to consume eventually destroy themselves by evaporating their mass and energy in the form of radiation. Hence according to Hawking’s theory, black holes can be regarded as the universe recycling machines.
“The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time.”
— Subrahmanyan Chandrasekhar (1910–1995)
Understanding black holes mean understanding the mysteries of gravity and hence the mysteries of the entire universe. Black hole singularities are very similar to the big bang singularity hence their proper understanding can provide us with a great deal of information about the beginning of the universe.