Supernovas: The Beginning
What exactly is a black hole? And how do we "see" black holes if they emit no light? And can a black hole really be a “wormhole” or “time machine” as the sci-fi authors claim?
Imagine you are a spectator in the cosmos, you have an all-seeing eye, and choose to zoom in your lens to the center of our galaxy at around 35,000 and 100,000 BCE. A star is nearly at the end of its life- it has depleted nearly all of its supply of hydrogen. It now sustains itself by fusing the heavier and heavier elements, up until it reaches iron. Iron is no longer able to supply enough energy to prop up the star's outer layers- and they start collapsing inward and then explode out. You are witness to a bright burst of light and color- a supernova.
The Black Hole
You shield your eyes from the brightness. Yet, a small part of the star remains behind. This remaining star's powerful gravitational force overwhelms everything else and it is crushed to an infinitely small point with infinite density, according to NASA.
In the words of astrophysicist Neta Bahcall, of Princeton University, a black hole is "Basically, an object or a point in space where the gravitational pull is so strong that nothing can escape from it".
The center of this point in space is known as the point of singularity, where all known laws of physics break down. The black hole then keeps increasing its mass by absorbing particles.
How Do You “See” a Black Hole?
Let us consider a cloud of gas that is around the black hole. The black hole's gravity causes the particles in space to orbit the black hole, black holes don't exactly “suck” them in, as popular narratives say. However, the gas particles constantly collide with each other, converting some of the kinetic energy into heat. With the loss of kinetic energy, the particles get closer to the black hole, until eventually, they fall in.
This kinetic energy is converted to thermal energy, and the particles heat up. Just before the gas actually enters the black hole, it heats up enough to begin glowing. Since this light is emitted by the gas before the gas enters the black hole, the light can escape the black hole, and reach our detectors. Therefore, we can indirectly "see" a black hole by seeing the glowing gas cloud that surrounds it.
Wormholes: Making Space Travel Possible
Now, you want to take that black hole and make it into a wormhole to travel through space-time. You know that theoretically and mathematically, they can be possible.
However, you doubt it, the way that it violates the causal structure of the universe, and the rules of space-time, causing several time travel paradoxes. But you want to try, anyway.
All you have to do to make that possible is take your black hole and connect it to a white hole. A white hole is a hypothetical object that expands outwards from a space-time singularity and emits energy- basically, a time-reversed black hole. Even if you somehow manage to connect the two in a tunnel, as soon as they form, their enormous gravitational strength rips them apart faster than the speed of light, making them terribly unstable to be of much use.
Exotic Matter
The only known way to stabilize a wormhole is to use some form of exotic matter, something with a negative mass. Put simply, a positive mass attracts things towards it, using gravity, while an anti-mass would repel things, hence providing repulsion to keep the black holes open as someone passes through it.
Initially, the closest known real representative of such exotic matter is a region of negative pressure density produced by the Casimir effect. The exotic matter will be able to counteract the massive effects of gravity, exerting a pressure greater than the pressure of the center of neutron stars, and thus prevent the wormholes from closing the instant they are formed.
Quantum Fluctuations: Fiction or Reality?
We might have a possible candidate for negative mass: the vacuum of space itself. Quantum Fluctuation in empty space is constantly creating a pair of particles and antiparticles only to be annihilated an instant later. And the vacuum of space is boiling with them. We can already manipulate them to create an effect similar to a negative mass.
Of course, there is a possibility that wormholes, although theoretically possible, might be impossible to exist in the real world. General Relativity is a mathematical theory that has a number of solutions, but it is not necessary for all of the solutions to describe reality. Coupled with the fantastic amount of energy required to warp the entire fabric of space-time and sculpt such a thing, the prospects of being able to create wormholes for time travel or space travel remains still in the minds of science fiction authors.
We might have a possible candidate for negative mass: the vacuum of space itself. Quantum Fluctuation in empty space is constantly creating a pair of particles and antiparticles only to be annihilated an instant later. And the vacuum of space is boiling with them.
We can already manipulate them to create an effect similar to a negative mass. Of course, there is a possibility that wormholes, although theoretically possible, might be impossible to exist in the real world.
General Relativity is a mathematical theory that has a number of solutions, but it is not necessary for all of the solutions to describe reality. Coupled with the fantastic amount of energy required to warp the entire fabric of space-time and sculpt such a thing, the prospects of being able to create wormholes for time travel or space travel remains still in the minds of science fiction authors.
We might not know what goes on in the center of black holes just yet, but wormholes and intergalactic travel will likely remain in speculations and popular science fiction just yet.