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The Slow Zone, also known as the Ring Space or the Hub, is a location that can be accessed from the "normal" universe via the Ring network. It is a black, starless spherical space approximately one million kilometers across, with 1,373 individual Ring Gates spaced equally around its periphery. At the center of this space sits the Ring Station.
- Main article: Slow zone incident (Books)
The slow zone was named for its absolute speed limit of six hundred meters per second. Any object with non-zero invariant mass moving faster than this limit is locked down by an inertial dampening field and then begins to move towards the central Ring Station, forming a ring around it. Light still acts normally and adheres to the speed of light, but radiation made up of larger particles like alpha and beta radiation does not exist inside the slow zone.
After the flotilla succeeded in following The Investigator's advice and powered down their ships, the speed limit inside the slow zone was lifted and all rings that still had an active ring on the other side reactivated. Following this, the area became known as "the hub".
The retrofitted OPA ship Behemoth relocated permanently to the hub and became Medina Station. The slow zone is blockaded at the Sol Ring by the United Nations and the Martian Congressional Republic. Refugee Belters from Ganymede, however, break through the blockade, enter the slow zone, and rush out to the later-named Ilus system.
Communication from the Sol system to the Slow Zone and Medina Station is lost following the breakout of the Free Navy Conflict. This occurred with the help of the once OPA-backed Captain, Christina Samuels, who switched to the Free Navy and halted all traffic through the Slow Zone. Colony worlds also lost communication to the Slow Zone - except for the Laconia system, since they were allied with the Laconian Imperial Navy, which controlled it.
Six months after the Consolidated Fleet defeats the Free Navy in the Slow Zone, James Holden proposes what will become the Transport Union. It will be run by Belters and will manage the flow of ships in and out of the Slow Zone.
- Main article: Third Battle of Medina Station
The Laconian Empire takes control of the Slow zone following the emergence of the Heart of the Tempest and the Gathering Storm from the Laconia gate.The Tempest uses its USM field projector to take out the Tori Byron, a Transport Union ship, and the Ring station railguns. The Storm at the same time takes out Medina's weaponry. It later discovered that the Tempest's field projectors caused the release of Gamma rays in the gates, which causes ships to go dutchman. This is information is used by the Laconians as a possible method to defend the Slow zone from any attacks from any gate.
- Main article: Tecoma star collapse
A weapons test is conducted in the Tecoma system against the Unknown Aggressors by the Laconian Empire. The weapons test involved detonating ships going dutchman but the test results in the Unknown Aggressors responding by adding extra mass in the Tecoma system. This added mass causes Tecoma's neutron star to collapse into a black hole and for the star to shoot out a gamma ray burst that hits the Tecoma gate. The Gamma ray then enters the Slow zone and hits the Thanjavuor gate as well. Both Ring gates are destroyed in the incident. The event also results in the Ring station glowing like a faint star and the edge of the ring space glowing with many colors.
- Main article: Slow zone catastrophe
Following the Tecoma star collapse, a time skip event occurs where the Unknown Aggressors disintegrates nearly every man-made object and human in the Slow zone. This involves the destruction of Medina station and the Eye of the Typhoon. Without Medina station, traffic through the rings becomes dangerous and unpredictable with no-one controlling ship transits. The destruction of the Typhoon also causes the Laconian Empire to lose full control over the slow zone. Only the Laconian imperial ship, the Falcon, is able to escape the catastrophe with the help of Elvi Okoye.
According to information retrieved by the Adro Diamond, the Ring Space was constructed following the Ring Builders' discovery that their universe lay adjacent to another, older universe or parallel reality. They devised a way to create a "bubble" of normal spacetime within this other universe, which could then serve as a hub for their Ring network. The Ring Station actively maintains the integrity of this bubble, utilizing energy derived from the "pressure" the exterior universe places on the Ring Space to generate "lines of force" that in turn support the bubble.
The region beyond the boundary of the Ring Space and between the Rings themselves is an entire universe inhabited by the Unknown Aggressors. These beings appear to be harmed or antagonized by the Ring Space's existence, and especially when the Rings are used to transport objects. For this reason, they declared war on the Ring Builders and set about trying to destroy them, and were eventually successful.
Following the Battle for the Ring station and defeat of Winston Duarte by James Holden and Aliana Tanaka, Holden makes the decision to destroy the Slow zone to prevent the Unknown Aggressors from destroying humanity and not going with Duarte's plan to make humanity a hive mind. This causes every colony world in the 1,300 worlds to be cut off from each other and the Sol system.
Images and video from Kelvin Paul Marchioro. 
- The "speed limit" is described as an active defense mechanism of the Ring Station in Abaddon's Gate, rather than a fundamental change in the constants of nature. "The speed limit grips the hull of the ships, but anything inside is unaffected." This effect is used as a key plot element throughout Abaddon's Gate. Bullets fired from weapons behave normally inside ships. However, when a Martian marine inside of the Ring Station attempts to launch a grenade, it "comes to a halt and drops to the ground centimeters from the barrel." When the speed limit comes into effect, crew and passengers are injured or killed due to the sudden deceleration of their ships' hulls.
- Initial readings also suggest that the background microwave radiation in the slow zone is older than the Big Bang.