A deep dive into Black Holes - one of the most majestic, mysterious and yet absolutely terrifying objects in the universe
Black holes are some of the most fascinating and mysterious objects in the universe. They are regions of space where gravity is so strong that nothing, not even light, can escape. But how do they form, what do they look like, and what happens near them? In this article, we will try to answer these questions using colloquial language and easy-to-understand examples.
Stellar Black Holes
Black holes are classified by their mass into four types: stellar, intermediate, supermassive and miniature. The most common (and thereby well-known) category of black holes is stellar black holes, which form as a result of a dying star. Black holes can develop when an immensely massive star depletes its fuel and collapses under its own weight. The resulting black hole is termed a stellar black hole, with a mass that can be several tens of times that of the sun.
The Anatomy of a Black Hole
According to Einstein’s equations, every black hole should possess what is known as a ‘singularity’ at its center — a theoretical point of infinite mass and zero volume. It is currently the subject of much scientific controversy; if the singularity truly has infinite density, then it would be a place where all laws of physics known to man should cease to apply. While physicists maintain that singularity exists, others disagree, asserting that such a point should be physically impossible. One thing for sure, however, is that if the singularity really does exist, that will be a place where all laws of physics known to man break down, implying we would not be able to predict what happens at the singularity.
The singularity is surrounded by a spherical boundary called the event horizon, which marks the point of no return for anything that crosses it. This is the ‘black’ part of a black hole, an absolute darkness where nothing, not even light, can escape to reach our sensors once it crosses over the event horizon. The event horizon can provide us with some intriguing insights about the black hole. For instance, in all black holes, the radius of their event horizon is directly proportional to their mass. This suggests that if we know how heavy the black hole is, we can reliably predict how wide its event horizon will be, and vice versa. For example, a black hole with the mass of the sun would have an event horizon radius of about 3 kilometers.
Accretion disks
‘Hold up,’ you say. ‘Didn’t they release a photo of a black hole a while back? If black holes are truly dark due to no light escaping, how’d they take a picture of it?’ That is a great question! Turns out, black holes are not actually completely dark. They can emit radiation and glow, but this is not the black holes themselves glowing; it is the matter that falls into them from their surroundings. The immense gravity of the black hole accelerates matter to speeds approaching the speed of light, resulting in superheating and radiation emission. This superfast matter also tends to form a disk around the black hole, called an accretion disk, because it gradually spirals inward due to friction and gravity. The accretion disk is very hot and bright because the matter in it is heated up by collisions and compression. This corresponds to the bright orange section visible in the photograph of the black hole shown above, Sagittarius A*(pronounced ay-star), a supermassive black hole that is in the center of our Milky Way galaxy.
Warping of the space-time continuum
The awesome gravitational wells of black holes have a profound impact on the fabric of spacetime around them. Due to their extreme gravity, they have the capability to bend light around themselves and distort the images of distant objects in a process called gravitational lensing. This is part of the reason why the accretion disks mentioned earlier actually look like they surround the black hole rather than intersect it: light from behind the black hole is warped around to form the image above, where the accretion disk seems to surround the black hole. Not only this, but black holes also slow down time near their event horizon, as predicted by Einstein's theory of general relativity. This means that an observer outside a black hole would actually see time pass more slowly than someone near a black hole. Time is not absolute.
Not only are black holes fascinating objects to study, but they also teach us a lot about physics and astronomy. They are natural laboratories for testing theories of gravity, such as general relativity and quantum gravity. They are also important for understanding how stars evolve and die, how galaxies form and grow and how matter behaves under extreme conditions. Black holes also inspire us to wonder about what lies beyond their event horizons, where our current knowledge fails. Who knows? There may be more to black holes than we ever imagined. Even the renowned astrophysicist Stephen Hawking once stated, "Black holes ain't as black as they are painted. They are not the eternal prisons they were once thought to be. Things can get out of a black hole both on the outside and possibly into another universe. So if you feel you are in a black hole, don't give up — there's a way out."