Black Holes Explained | They are not what you think they are! | Dhruv Rathee
Hello, friends! If you remember, in 2014, there was a blockbuster film by Director Christopher Nolan, Interstellar. In this film, space-related concepts such as wormholes, black holes, and alien planets were depicted in a scientifically accurate way. But perhaps the most shocking scene was at the end of the film.
In the climax, the main character of the film, Cooper, falls into a black hole. The black hole in the film is named Gargantua. Cooper, along with his spacecraft, plunges into the darkness of this massive object. Initially, everything around him is black—complete darkness. But as he falls deeper, he begins to notice some grain-like particles.
These particles hit his spacecraft, causing scratches. There are flashes of light, sparks, and eventually, his spacecraft catches fire. Forced to eject, Cooper continues to fall deeper into the black hole, until suddenly, he finds himself in a five-dimensional space—a tesseract. It was a mind-boggling experience, a place where he could communicate with his past self using gravity.
Seeing these scenes, you might have wondered: Is this actually possible? Does such a thing exist inside a black hole? What would we see if we were to fall into one?
“Black holes remained largely unknown until the 20th century. A black hole is a region in space where the force of gravity is so strong that not even light can escape.”
“From the outside, you can’t tell what is inside a black hole. Black holes haunt our universe—dark centers of gravity that swallow everything in their path.”
Einstein’s Theory of Relativity
Let’s begin with the story of black holes, friends. The history of black holes isn’t very long. A hundred years ago, no one knew about black holes. It was because of Einstein’s Theory of Relativity that black holes were later discovered.
Einstein’s theory consists of two parts: the Special Theory of Relativity and the General Theory of Relativity. The Special Theory of Relativity, published by Einstein in 1905, explains how speed influences time. If you’re in a spaceship traveling at an extremely high speed, time will slow down for you compared to those on Earth. This concept is known as Kinematic Time Dilation.
Not only speed, but gravity can also result in time dilation, as shown by Einstein in his General Theory of Relativity, developed in 1915. The more gravitational force you experience, the more time slows down for you. This phenomenon, called Gravitational Time Dilation, was depicted brilliantly in Interstellar when Cooper and his team land on the Aqua Planet, where one hour equals seven years on Earth due to the planet’s proximity to the Gargantua black hole.
To visualize this, Einstein wanted us to imagine space-time as a fabric, like a mesh on which all planetary objects are placed. The space-time fabric bends due to the mass of these objects. This bending not only attracts physical objects more but also leads to time dilation. Other forms of energy, such as sound, heat, or light, are also affected by gravity.
This led to the conclusion that objects could exist in the universe with such high gravitational force that they could completely absorb light, making them invisible to us. These objects are what we call black holes. But when Einstein first presented his Theory of General Relativity, the concept of black holes was merely theoretical.
Einstein knew that gravity could influence light and that theoretically, objects that could absorb light were possible. However, he did not believe that black holes existed in reality. In fact, when Einstein was alive, the concept of black holes seemed strange to him. He knew they could exist theoretically, just as the existence of infinity is possible theoretically, but he did not believe they were real. By the time he passed away, the term “black hole” hadn’t even been coined yet.
An interesting fun fact is that a key point in Einstein’s theory is that the speed of light limits gravity’s influence. We don’t feel gravity’s force instantly everywhere; its upper limit is the speed of light. For example, if the sun suddenly disappeared, it would take us 8 minutes to notice its absence on Earth because it takes 8 minutes for sunlight to reach us. Similarly, according to Einstein, the gravitational impact of the sun’s disappearance would also be felt 8 minutes later.
After Einstein, many scientists continued to work on the Theory of General Relativity. They solved equations and theoretically proved that black holes could indeed exist. By the 1960s, researchers and scientists had finally agreed that black holes were not just theoretical; they likely existed in space. The term “black hole” was first used in a magazine in 1964 but gained popularity after 1967 when physicist John Wheeler popularized it.
How Black Holes are Formed
Even though the term “black hole” sounds sensational, it is somewhat misleading. It might sound like there’s an actual hole in space, but that’s not the case. Black holes are formed by stars, meaning there is some material at their center. Our Sun is also a star, and at the center of stars, there are continuous nuclear fusion reactions that produce heat and light. This heat creates an outward force, while gravity pulls inward, keeping the star intact and alive.
Stars maintain this equilibrium throughout their lives, but when the fuel for these reactions (such as hydrogen or helium) runs out, the outward force ceases, and gravity causes the star to collapse in on itself. The fate of the star depends on its mass. If it was a small or average-sized star, it might turn into a Red Giant and then a White Dwarf or a planetary nebula. But if it was a massive star, it could become a Red Super Giant and then explode in a supernova, leaving behind a tiny core.
If the core is small, it becomes a Neutron Star, but if it’s larger, it can turn into a black hole. Essentially, a black hole forms when a star’s mass becomes so compressed that its volume shrinks dramatically. For example, if our Sun were to become a black hole, its diameter would be only 50 kilometers. However, our Sun is not massive enough to become a black hole. This was proven by the Indian-American astrophysicist Subrahmanyan Chandrasekhar, who developed the Chandrasekhar Limit. According to this limit, a White Dwarf’s maximum mass can be 1.4 times that of our Sun. Anything larger would become a Neutron Star or a black hole.
Types of Black Holes
There are mainly three to four types of black holes. The first is the Stellar Black Hole, the most common type, formed from stars. Scientists estimate that there are between 10 million to 1 billion such black holes in our Milky Way Galaxy.
The second type is the Primordial Black Hole, which is as small as an atom but with the mass of a mountain. These black holes are still hypothetical, and we don’t know much about them.
The third type is the Supermassive Black Hole, which is enormous, with a mass greater than 1 million Suns combined, fitting into a ball the size of our Solar System. Scientists believe that at the center of every major galaxy, including our Milky Way, there is a Supermassive Black Hole. The one in our galaxy is called Sagittarius A*.
In Interstellar, the black hole named Gargantua was depicted as a supermassive black hole. Additionally, scientists suspect the existence of a fourth type of black hole, the Intermediate Black Hole, which lies between the sizes of Stellar and Supermassive black holes, though no evidence has been found yet.
One thing to note is that black holes aren’t like giant black balls that suck everything in. The appearance of a black hole is more complex. The black hole in Interstellar was depicted in HD and with more three-dimensional detail than the first photo ever captured of a black hole.
The most notable feature is the orange-colored ring around the black hole, known as the Accretion Disk. This disk is formed from gaseous matter and debris attracted to the black hole by its immense gravity. The material in the disk heats up as it spins around the black hole, emitting electromagnetic radiation, mainly X-rays.
This accretion disk was depicted accurately in Interstellar, except for the color. The real color would be closer to blue, as X-rays are outside the visible light spectrum, but they are represented in orange-yellow for visual purposes.
In 2019, the first photo of a black hole was taken, showing a blurred image with a brighter side. The brighter side is due to the Doppler Beaming effect, where particles spinning towards us appear brighter than those spinning away.
The movie also depicted the accretion disk creating an optical illusion due to gravity, making it appear to cover the top and bottom of the black hole. This illusion is caused by gravity bending light. The area hidden behind the disk is revealed by the bending of light, creating a unique visual effect when viewed from the side.
Inside the black hole, there is a region known as the Photon Sphere, where the gravity is so strong that light orbits the black hole. If you were in this area, it might theoretically be possible to see the back of your head as light travels in a circle. Beyond this is the Event Horizon, the boundary where gravity is so strong that even light cannot escape.
If you fall into a black hole and cross the Event Horizon, there’s no chance of escape. In Interstellar, Cooper’s spacecraft crosses the Event Horizon, and he finds himself in a five-dimensional space. This part of the movie is purely speculative, as we have no idea what lies inside the Event Horizon.
Einstein’s General Theory of Relativity describes the center of a black hole as a Singularity, where the curvature of space-time becomes infinite. The space-time fabric stretches infinitely at this point, and time slows down infinitely.
What Happens if You Fall Inside?
But what does it mean for time to slow down infinitely? Does this mean that if you enter a black hole and somehow come out, the universe outside would have ended for the rest of us? We don’t know. We can only theorize. Some suggest that inside the Event Horizon, light reflects off multiple points before reaching Singularity, meaning that things might be visible inside.
The one thing we know for sure about black holes comes from the single photo taken by the Event Horizon telescope on April 10, 2019. This photo proved the existence of black holes about 100 years after they were theoretically proposed.
One thing is certain: if you fall into a black hole, the gravitational force will likely tear you apart within milliseconds. However, there’s no need to fear black holes. Earlier, people had the misconception that black holes would consume everything in the universe, but that’s not how they work.
Supermassive black holes at the center of galaxies, like Sagittarius A*, hold everything in their range in orbit, just as the Sun does with the planets in our Solar System. As long as you maintain a proper distance from a black hole, you’ll be safe.
“The concept of a five-dimensional space is purely theoretical and was used creatively in Interstellar to depict how time could be viewed as a physical dimension. The idea is that in a higher-dimensional space, you could potentially see all points in time simultaneously, like viewing an entire timeline from start to finish.”
“In the movie, Cooper experiences this when he finds himself inside the Tesseract, a construct that allows him to see different moments in time as if flipping through pages in a book. The depiction is fascinating but remains within the realm of science fiction.”
Hawking Radiation and the End of Black Holes
Stephen Hawking made a groundbreaking contribution to our understanding of black holes by proposing that they aren’t entirely black. Instead, they emit a type of radiation known as Hawking Radiation. This phenomenon suggests that black holes slowly lose mass and energy over time, eventually leading to their evaporation and disappearance.
Hawking Radiation arises from quantum effects near the Event Horizon, where particle-antiparticle pairs are generated. One particle falls into the black hole, while the other escapes, leading to a net loss of mass for the black hole. Over billions of years, this process could cause the black hole to evaporate completely.
While the concept of Hawking Radiation has not yet been observed directly, it is widely accepted in the scientific community and adds another layer of complexity to the nature of black holes.
Black Holes and the Future of Space Exploration
The study of black holes is crucial for understanding the fundamental laws of physics. They challenge our understanding of gravity, quantum mechanics, and the nature of space and time. As our technology advances, we may eventually be able to observe black holes more closely and unlock the secrets they hold.
Moreover, black holes have inspired countless works of science fiction and continue to capture the imagination of people around the world. The depiction of black holes in movies like Interstellar has brought these cosmic phenomena into the public eye, sparking curiosity and wonder.
As we continue to explore the universe, black holes will remain one of the most mysterious and intriguing objects in space. Who knows what future discoveries await as we peer deeper into the darkness, seeking to understand the very fabric of the cosmos?
Conclusion
Black holes are among the most fascinating and enigmatic phenomena in the universe. They challenge our understanding of physics and push the boundaries of what we know about space, time, and gravity. From their theoretical conception by Einstein to the stunning visualizations in films like Interstellar, black holes continue to captivate scientists and the general public alike.
The study of black holes is not just about understanding these mysterious objects themselves but also about gaining deeper insights into the nature of the universe. They offer a glimpse into the extremes of physics and provide a natural laboratory for testing our theories of gravity, quantum mechanics, and more.
As we continue to develop more advanced technology and methods for observing the cosmos, we may one day unravel the mysteries of black holes. Until then, they remain a profound reminder of how much there is still to discover in the universe.
Thank you for joining me on this journey through the wonders of black holes. If you’re fascinated by the cosmos and want to learn more about space, time, and the mysteries of the universe, I invite you to visit my other blogposts, where we delve into these topics in greater detail.
Until next time, keep exploring, keep questioning, and keep looking up at the stars!