Fiction:Virgo Birch Planet

"This is then about the largest black hole that could be used for a simple 1g suprahole planet."

- Paul Birch

The Virgo Birch Planet is light year-sized artificial planet with a hypermassive black hole at its core. The planet was constructed by the Kardeshev III Builder Civilisation from all the mass of their home Pristini Galaxy.

In principle, a Birch planet is an artificial world where the surface gravity is provided by a galactic-mass black hole at the planet's core. The livable area on the surface exists as many shell-worlds of material that are held apart from falling into the black hole by active support.

The Virgo Birch Planet is one of the largest and mysterious single objects in the vicinity of the whole First Gigaquadrant. Because of its huge mass and surface area, the planet can be classified as a galaxy, although not in the conventional, natural sense.

Location
The Virgo Birch Planet exists in the former location of the Pristini Galaxy, 5 million light years from its nearest neighbor, Cyrannus. This places the planet just outside the galactopolitical region known as the First Gigaquadrant as it does not fall inside any of the galaxy groups considered to be part of that entity.

The planet sits alone is space, not orbiting any other body. However, many smaller bodies orbit it in a geocentric pseudo-star system. These bodies include rouge planets, stars, and even multiple Dyson Spheres. Over time, the planet has also accumulated a halo of new dark matter.

Observability
As the planet does not orbit any star, it gives of very little light. This, coupled with the fact that the physical size of the planet is actually very small on an intergalactic scale, makes the planet virtually impossible to see directly. This explains why the planet went undiscovered by modern 29th century civilisation until relatively recently.

Detection of the planet is possible through observation of its indirect gravitational effects on nearby dwarf galaxies such as the PGC 170257 and PGC 45628 irregular galaxies. In the past, the flurry of gravitational waves emitted from the thousands of black hole-merger events that occurred in the planets construction would have also been detectable from the Gigaquadrant galaxies and may have been recorded by ancient civilisations. Also, the visible disappearance of the Pristini Galaxy over this period of constructed would have been directly observable.

Architecture
Fiction:Virgo_Birch_Planet/Crust|Crust Fiction:Virgo_Birch_Planet/Void|Void Mantle Fiction:Virgo_Birch_Planet/Azathoth-3S|Azathoth-3S

Construction
The Builder Civilisation began construction of the Birch Planet between 1.5 and 1.2 billion years ago in the now totally converted Pristini Galaxy. This involved feeding the central supermassive black hole of the galaxy, K37 Gem 9, the vast majority of the matter making up the galaxy so that it would be of appropriate mass to act as the core of the vast planet. The hypermassive Azathoth-3S black hole that would go on to become the core of the planet was formed as a result. This was accomplished through the movement of all 800 billion stars in the galaxy towards the center by renovation of the billions Dyson spheres that already comprised the Builder's empire into Shkadov thrusters. To avoid crowding of the central galactic area with too many stars, many were merged into smaller intermediate-mass black holes to compact many dozens of solar masses into a smaller volume. These were the actual objects fed into K37 Gem 9. By some unknown means, the diffuse gas and dark matter that made up a significant portion of the galaxy's mass was also fed into the black hole. This process occurred first as many Dyson spheres had vital functions to the empire that needed to be maintained as long as possible. This period changed the face of the Pristini Galaxy forever and is known as the Great Contraction.

This subluminal, brute-force approach was chosen by the Builders rather than the large scale superluminal transport of matter through structures such as wormholes. The actual time it would take to contract the whole galaxy was a largely unimportant factor to consider due to the Builder's extreme automation technology and due to the fact that virtually all Builder citizens lived as digital beings in simulated realities on the vast technoospheric network of matryoshka brains that extended across Pristini. These simulation could slimply be run at a slower speed so that the speed of the exterior real universe accelerated by comparison.

The shell of the planet was build by large spacebourne robots in large terastructural sections which were then lowered down and put into place by robots closer to the black hole. This was done because all the shellworlds at a lower altitude than the black hole's photon sphere, and thus ships would require a more energy-expensive superluminal propulsion systems to remain in orbit. The matter used to construct the shell itself came only comprises a miniscule amount of what used in the construction of Azathoth-3S. Thus, most of it came from just the residual Dyson spheres that weren't vital to the black hole. Stellar plasma and diffuse interstellar hydrogen could be made into the heavier elements needed by very large-scale industrial fusion. The process of Matter Enlightenment was also used to convert dark matter into standard elements.

It is not known why the Builders decided to construct the Virgo Birch Planet as there are many other K3 megastructures that would provide vastly more surface area to live on, or power generation. The answer to this ancient civilisation's motives puzzles xenoanthropologists and philosophers to this day.

Azathoth-3S
Azathoth-3S is the name given to the hypermassive black hole at the core of the planet. The "3S" in its name refers to its mass of approximately 3 sortatonnes. This mass is approximatley equal to that of the whole Pristini Galaxy before the Great Contraction, including the all the stars, diffuse gas, and dark matter.

This mass gives the black hole a radius of 0.47 light years, which is approximately 200 million times larger than average supermassive black holes found at the center of galaxies.

Azathoth-3S provides the mass needed for the surface gravity of the livable layers of the planet. because the mass it so large, the suface gravity decreases very gradually with distance from the event horizon, so a large distance of livable area with comfortable surface gravity could be spanned.