Black Hole

A **black hole** is a region of spacetime exhibiting gravitational fields so strong that nothing, not even electromagnetic radiation such as light, can escape. As a result, they do not emit light, hence their name. Supermassive black holes of billions of solar masses are at the centre of most galaxies, while black holes made out of collapsed dark matter are known as primordial black holes.

Black holes have had important roles in the *Hyperion* Saga, as the singularities within them act as portals to other locations in spacetime, similar to wormholes; unlike wormholes, singularities can only be traversed through lightfolding, and, unless the ship has enough energy to break back through the opposing white hole, are only one-way.

## Properties & Structure

Once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, electric charge, and angular momentum; the black hole is otherwise featureless; therefore, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another. These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law (through the ADM mass), far away from the black hole.

When an object falls into a black hole, any information about the shape of the object or distribution of charge on it is evenly distributed along the horizon of the black hole, and is lost to outside observers. The behavior of the horizon in this situation is a dissipative system that is closely analogous to that of a conductive stretchy membrane with friction and electrical resistance—the membrane paradigm. This is different from other field theories such as electromagnetism, which do not have any friction or resistivity at the microscopic level, because they are time-reversible. Because a black hole eventually achieves a stable state with only three parameters, there is no way to avoid losing information about the initial conditions: the gravitational and electric fields of a black hole give very little information about what went in. The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including approximately conserved quantum numbers such as the total baryon number and lepton number.

### Event Horizon

The defining feature of a black hole is the appearance of an event horizon, a boundary in spacetime through which matter and light can pass only inward towards the mass of the black hole. Nothing, not even light, can escape from inside the event horizon unless it is moving at FTL speeds. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine whether such an event occurred.

To a distant observer, clocks near a black hole would appear to tick more slowly than those farther away from the black hole. Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it. At the same time, all processes on this object slow down, from the viewpoint of a fixed outside observer, causing any light emitted by the object to appear redder and dimmer, an effect known as gravitational redshift. Eventually, the falling object fades away until it can no longer be seen. Typically this process happens very rapidly with an object disappearing from view within less than a second.

## Traversal

Unlike wormholes, black holes only connect to one constant place in space-time, and can only be traversed by a ship going faster than the speed of light. Missing the singularity by even a few meters will pull the ship into the black hole, destroying it for eternity due to the time dilation. This is a process called spaghettification.

## Notable Black Holes

* Charybdis - supermassive black hole at the centre of the Whirlpool Galaxy
* Cetus - supermassive black hole at the centre of the Andromeda Galaxy
* Gaping Maw - a primordial black hole located in the Aschere System
* M51b Gateway - a black hole that serves as a one-way link to the Prison Dimension
* Sagittarius - supermassive black hole at the centre of the Milky Way