Immediately after the Big Bang, when the Universe was nothing more than a hot sea of subatomic particles, photons crashed into and scattered off of everything they encountered. Then, as space expanded and time elapsed, various different regions of higher energy began to have the same pressure as regions of lower energy. Gradually, certain sectors of the Universe were able to collapse into the seedlings of primordial Black Holes. Eventually, these structures were compressed into such a dense state that they achieved a critical surface limit with an escape velocity equal to the speed of light, thus giving rise to the first generation of Black Holes. About 13.2 billion years ago, the supermassive black hole that exists at the center of the Milky Way Galaxy was born. They call it Sgr A*.
Since light is unable to reflect off of a Black Hole, it’s only possible to measure a small number of properties like the mass, electric charge, and rate of rotation of these otherwise mysterious celestial bodies. It is said that most physical quantities take on infinite values under the extreme conditions of absolute pressure, so the ordinary laws of physics do not apply to the scale at which a singularity exists. This occult point at the center of a Black Hole contains the entire mass of the object. In many ways, Sgr A* is the heart of the Milky Way, or the stomach maybe.
These seemingly insatiable, voracious, beasts of nature are capable of devouring anything in their grasp, and they can grow to an incomprehensible size. As an example, Sgr A* is about 3.5 million times the mass of the Sun with a diameter of 10 million miles, whereas the unimaginably vast Black Hole at the center of Galaxy M87 is around 6.5 billion times the mass of the Sun and 20 billion miles in diameter. This is important because, the size of a Black Hole is determined by the diameter of its event horizon, and the diameter of an event horizon is directly related to a Black Hole’s mass, such that for each solar mass of material the diameter of an event horizon increases by about six kilometers.
As enormous and unstoppable as this may seem, these astronomic objects are not at all indestructible. Although most Galaxies are being pushed away from each other by levity, there are a few Galaxies that are being pulled toward each other by gravity. Those Galaxies become locked in a collision course until they attract and merge with one another. Because the Milky Way and the Andromeda Galaxies are so big and close to each other, they will eventually experience this about 4 billion years from now, ejecting a number of Stars in the process. Then, after the Universe has evolved for trillions of years, entropy will finally bring about the breakdown of all matter through the systematic evaporation of Black Holes into loosely bound particles that eventually decay, leaving nothing behind. In the end, Sagittarius A* will vanish out of existence, just as bizarrely as it emerged.