Black Holes 101

Black holes are extremely intriguing celestial objects that continue to baffle scientists. These enigmatic entities are regions in space where gravity is so overpowering that even light, the fastest-known entity in the universe, cannot escape their grasp.

The black hole's boundary, known as the event horizon, marks a point of no return. Once an object crosses this boundary, it collapses into the black hole's singularity. This singularity is an infinitesimally small and infinitely dense point where the normal laws of physics, time, and space no longer apply.

Scientists have proposed various types of black holes, but the most common ones are stellar and supermassive black holes.

Stellar black holes form when massive stars reach the end of their lives and implode. These black holes typically have a mass 10 to 20 times greater than that of our sun and are scattered throughout the universe. It is possible that the Milky Way alone harbors millions of these stellar black holes.

Supermassive black holes, on the other hand, are colossal in size, measuring millions or even billions of times the mass of our sun. Although their formation remains a mystery, we do know that they exist at the centers of many large galaxies, including our own. For instance, Sagittarius A, the supermassive black hole residing at the heart of the Milky Way, has a mass roughly equivalent to four million suns and a diameter comparable to the distance between the Earth and the sun.

Since black holes are invisible, scientists rely on observing their influence on nearby matter to detect and study them. This includes observing accretion disks, which form when gases and dust fall toward a black hole, as well as quasars, which are jets of particles emitted by supermassive black holes.

It wasn't until the 20th century that black holes started to be better understood, thanks to advancements in scientific knowledge. In 1916, a German physicist named Karl Schwartzschild, utilizing Einstein's general theory of relativity, calculated that any sufficiently compressed mass could become a black hole.

However, it wasn't until 1971 that the existence of black holes was confirmed. Astronomers discovered the first black hole while studying the constellation Cygnus. These captivating objects, scattered throughout the universe, continuously warp space and time, influencing entire galaxies and captivating the imagination of scientists and the general public alike.

In their core, nuclear fusion crushes hydrogen atoms into helium releasing a tremendous amount of energy This energy, in the form of radiation, pushes against gravity, maintaining a delicate balance between the two forces.

As long as there is fusion in the core, a star remains stable enough. But for stars with way more mass than our own sun the heat and pressure at the core allow them to fuse heavier elements until they reach iron.

Unlike all the elements that went before, the fusion process that creates iron doesn't generate any energy. Iron builds up at the center of the star until it reaches a critical amount and the balance between radiation and gravity is suddenly broken. The core collapses. Within a fraction of a second, the star implodes.

Moving at about the quarter of the speed of light, feeding even more mass into the core. It's at this very moment that all the heavier elements in the universe are created, as the star dies, in a super nova explosion. This produces either a neutron star, or if the star is massive enough, the entire mass of the core collapses into a black hole. If you looked at a black hole, what you'd really be seeing is the event horizon.

Anything that crosses the event horizon needs to be travelling faster than the speed of light to escape. In other words, its impossible. So we just see a black sphere reflecting nothing. But if the event horizon is the black part, what is the "hole" part of the black hole? The singularity. We're not sure what it is exactly.

A singularity may be indefinitely dense, meaning all its mass is concentrated into a single point in space, with no surface or volume, or something completely different. Right now, we just don't know. its like a "dividing by zero"error. By the way, black holes do not suck things up like a vacuum cleaner, If we were to swap the sun for an equally massive black hole, nothing much would change for earth, except that we would freeze to death, of course what would happen to you if you fell into a black hole?

The experience of time is different around black holes, from the outside, you seem to slow down as you approach the event horizon, so time passes slower for you. at some point, you would appear to freeze in time, slowly turn red, and disapear. While from your perspective, you can watch the rest of the universe in fast forward, kind of like seeing into the future.

Right now, we don't know what happens next, but we think it could be one of two things: One, you die a quick death. A black hole curves space so much, that once you cross the event horizon, there is only one possible direction. you can take this - literally - inside the event horizon, you can only go in one direction. Its like being in a really tight alley that closes behind you after each step.

The mass of a black hole is so concentrated, at some point even tiny distances of a few centimeters, would means that gravity acts with millions of times more force on different parts of your body. Your cells get torn apart, as your body stretches more and more, until you are a hot stream of plasma, one atom wide. Two, you die a very quick death. Very soon after you cross the event horizon, you would hit a firewall and be terminated in an instant.

Neither of these options are particularly pleasant. How soon you would die depends on the mass of the black hole. A smaller black hole would kill you before you even enter its event horizon, while you probably could travel inside a super size massive black hole for quite a while. As a rule of thumb, the further away from the singularity you are, the longer you live.