Orbiting in Mystery - The Dark World of Black Holes
1915 - the year Albert Einstein first predicted the existence of black holes in his theory of general relativity. Since then, science has developed at an exponential rate, creating groundbreaking discoveries that continue to revolutionise the world of modern science. However, scientists have been striving to understand the truth behind black holes for more than a century, with many mysteries still waiting to be uncovered. Then there’s the overarching question: what really is a black hole, and what goes on inside of it? Why did scientists take so long to capture a single image of a black hole in 2019, and if black holes cannot be seen with the naked eye, how were they discovered to begin with?
How They Form: The Birth of a Black Hole
Stars are constantly in a battle against gravity. Gravity naturally tries to collapse stars, which retaliate by creating pressure from the heat generated in their core. This constant pushing and pulling creates peace between the two forces, allowing the star to maintain its form. However, the heat in a star’s core is generated by chemical reactions, meaning that when the star runs out of the material required for those reactions, it cannot maintain its form - a supernova explosion occurs.
Image Credits: NASA/CXC/M.Weiss https://spaceplace.nasa.gov/supernova/en/
Whilst smaller stars convert into dense neutron stars, larger stars around three times the mass of the Sun turn into black holes. There are four types of black holes that we know of:
Miniature/Primordial: Born within a mere second of the Big Bang. Can range from a size of 0.00001 times the mass of a paperclip to 100,000 times the mass of the Sun.
Stellar: The imploding star is between eight to 20 times the mass of the Sun.
Intermediate: As the name suggests, a black hole with a size between that of a stellar black hole and a supermassive black hole. Rare, formed by having multiple stellar black holes merging with one another.
Supermassive: There are many theories about how supermassive black holes can form, but one of the theories is that the black hole consumes so much material (including fellow black holes) that it reaches its supermassive size.
In summary, the reason black holes are formed is due to the gravity of a star overpowering the star’s ability to add pressure back, resulting in a collapse onto itself.
Death of Black Hole: Is it possible?
Black holes don’t exactly die. Rather, it is believed that they evaporate by losing mass and slowly disappearing, but the evaporation process is so slow that it would take billions of years for them to fully disappear.
Black holes have long been believed to only maintain or increase in mass, as they inescapably absorb everything. So how is it possible that black holes evaporate and "die"? The answer is something called Hawking radiation, named after Stephen Hawkings, a famous English theoretical physicist. Hawking radiation is a theory that changes the way black holes are perceived. It is when black holes lose particles and mass, making them slowly evaporate. Then how did those particles escape the black hole’s gravitational pull - a pull always thought to have been so powerful that not even light could escape it? It turns out that this theory alo shows that black holes radiate thermal energy and consequently lose mass.
This happens when pairs of particles get split near the event horizon. One particle gets stuck in the gravitational pull of the black hole whilst the other escapes. The particle that escapes takes some of the black hole’s mass with it, which causes the black hole to lose mass. Although the net loss of mass cannot be measured with the technology we have now, and the amount of mass lost widely depends on the size of the black hole, it is still theorized that mass is lost. The process is just painstakingly slow, which is why it is hardly noticeable and has only recently been detected.
Black holes’ deaths are detected using gamma-ray detectors, as evaporation results in an explosion of gamma rays. Although many of these bursts have been detected, none match the pattern of what would theoretically occur if a black hole were to evaporate. It just takes so long that no scientists have ever even detected any black hole evaporations. Meanwhile, scientists were busy trying to take a picture of a black hole for the first time ever, and they actually succeeded!
Why Can’t We See: Reflection of light
Only recently, a team of scientists was able to take a picture of a black hole. In fact, it was only 2 years ago, on April 10th, 2019, when the first image was captured by Katie Bouman.
Image Credits: Jason Major
People around the world were amazed by how this phenomenon had been achieved. Why? Well, they had never known what a black hole looked like until that day. All we could do was simply imagine what a black hole looked like. But why can’t black holes be seen with the naked eye? Before explaining why, we first need to understand the basic concept of seeing objects. Light from a source (such as the Sun, fire, light bulb, etc.) shines at an object, and reflects back into our eyes - allowing us to see that object. However, a black hole does not reflect any light from any source. The reason for this is, once again, because black holes don't let anything - including light - escape from their powerful gravitational force. Therefore, you cannot see a black hole because it doesn’t reflect any light for our eyes to receive
So if black holes cannot be seen, how did scientists discover them? Read on to find out!
Discovery of the First Black Hole: Cygnus X-1
Geiger–Müller counters: An instrument used to detect the presence of gamma, alpha, or beta radiation. Invented in 1911 by Hans Geiger and Walther Müller.
New Mexico, 1964. A pair of Geiger–Müller counters were launched to space via a rocket. The counters detected a blue supergiant star orbiting something massive around 7,200 light years away from Earth. As it orbited, the gas from the star was shown to be sucked into the mysterious object, emitting high-energy X-rays and gamma rays. This allowed the Geiger–Müller counters to detect a presence - Cygnus X-1, the first ever black hole discovered.
According to a recent study published by Science, Cygnus X-1 has a mass of 21 Suns, making it the largest black hole to ever be discovered without the use of gravitational waves. (Since then, scientists have found hundreds and hundreds!) Cygnus X-1 is also spinning at speeds never seen before in any other black hole since discovered.
Thus, although it’s been over half a century since its discovery, Cygnus X-1 continues to reveal more and more groundbreaking findings about the nature of black holes.
What’s Inside of a Black Hole?
We all know that black holes suck in almost everything that passes their way, but how do we know what happens to those things? What is actually inside of them? No one knows exactly what lies within a black hole because no astronauts have gone inside to explore and ever come out alive. The closest black hole to Earth is 1,500 light-years away (8 trillion miles!), which would be about 36,411,837,700 times the distance of the moon to the earth, which is 384,400 km. Even if we could find a way to travel that far and make it there alive, we would still face the challenge of communication which, in that context, isn’t possible with the knowledge that we have right now.
The black hole has an event horizon, which acts as a barrier between space and the hole. Anything that crosses the event horizon, including light, has no chance of returning.
YouTube: What's Actually Inside A Black Hole?
It is believed that within the black hole there is something called a singularity point. A singularity point is something that has no mass or size, so technically it is just space where everything has a density of infinity. Everything in the singularity point is so mutated that everything is equal and squeezed to become infinitely small. Anything that falls in the black hole gets pulled and stretched in all directions because of the very strong gravitational pull it has. This process is called spaghettification.
Image Credits: Katherine Streeter for NPR
No one knows what lies beyond the event horizon and what happens to anything that gets sucked into it, but what would happen if humans found a way to enter black holes? What fate would they meet?
Entering the Abyss: What happens when humans enter black holes
Even though scientists were successful in taking a picture of the black hole, we were never able to go inside. But what if one day, you fell into a black hole? Would you survive? What would you discover?
A black hole’s gravity is so strong, even light can’t escape. Scientists say that the gravity of black holes is approximately 4 times the gravity of the Sun. So if you fell into a black hole, feet first, your legs would feel a very strong gravitational pull compared to your head.
A common type of black hole found in our space is called the “stellar” black hole. They can stretch up to 9 miles (15 km). The gravity would be 20 times heavier than the Sun! If you entered one of these black holes, you would be completely torn apart. However, if you entered a larger black hole, your body would be unharmed. Since the gravity is too strong, it would suck in both your head and legs with the same strength. And how big would the black hole have to be? Well, the gravity would have to be about a million times heavier than our Sun. Here, you could pass the event horizon of the black hole. But this would just be the start. The next challenge would be the gravitational singularity, which is located at the center of the black hole. Here, sadly you wouldn’t be able to come back. There is absolutely no return from the event horizon, and even if there were, the gravity and stretching (spaghettification) at the singularity point would kill you.
And, just for fun, what if you saw a person falling into a black hole? A very realistic question to answer! As they fall into the black hole, you wouldn't see them stretching, but they'd slow down. They would also look dimmer and redder, and, in the end, frozen!
Preserving Time: Using Black Holes to Stop Time
Time travel has always been a fascinating topic throughout history until today. Many scientists have searched for a way to time travel but none have been successful yet… Could black holes possibly be the answer? According to the general relativity theory, gravity affects space and time. Black holes have very strong gravitational pull, which could allow them to be used to stop time.
The speed at which the time would slow would depend on the gravitational pull the black hole would have. For example, if you were to make it in a black hole or even get close to one, those watching from a distance would see you moving very slowly while actually, from your point of view, you would be moving at a perfectly normal speed. This would be similar to traveling in the future, except it wouldn’t speed up the time around you, but rather, slow you down.
To conclude, no matter how much science progresses, there are constantly new developments and mind-boggling mysteries that confound us. That’s part of the beauty that comes with the universe: there’s always something to explain, something to make sense of. Back when the idea of black holes was first established, scientists were baffled by how black holes defied so many theories that had been the bedrock of science. Since then, we've come a long way.
But as we delve deeper into the vastness of space, we continue to learn just how much we really don’t know!