Solakku is the star at the centre of the avali home system. It is chemically peculiar and roughly classifiable as an A-type main-sequence star. It orbits the galactic enter at a distance of 8200 light-years on average and is approximately 6.4 astronomical units (960,000,000 km) away from Avalon. This corresponds to about 53 light-minutes.

Solakku forms a binary solar system together with its red dwarf companion Crest. Alone, Solakku contains 91.29% of the total mass of this system and together with Crest, the two stars hold 99.77% of the total mass.

Like other main-sequence stars, Solakku produces energy through nuclear fusion of Hydrogen into Helium and emits most of this energy through light, in its case mostly visible light and infrared.

Composition

Solakku
	; Solakku, viewed through a solar filter
Characteristics
Evolutionary stage	Main Sequence
Spectral type	kA5hA8mF4
B−V color index	0.27
Details
Mass	1.549 M☉
Radius	1.559 R☉
Luminosity	8.166 L☉
Temperature	7803 K
Metallicity [Fe/H]	0.178 dex
Age	2.6 billion years
Orbit
Mean distance from Milky Way core	8200 light-years
Galactic period	45 million years
Velocity	340 km/s about Galactic Center

Solakku consists mainly of hydrogen and helium, though the composition is different between what is observable in the photosphere and what is present in the core. As it is already 77% through its total lifespan, Solakku’s core consists of 82% helium, with the remaining 18% being mostly hydrogen.

The measured photosphere composition is 78.3% hydrogen and 19.1% helium. Metals account for the remaining 2.6%, most notably 0.25% iron and traces of Calcium. This is an unusual high metallicity for an A-type star, making it an Am-type chemically peculiar star. This makes classification difficult. Visually, Solakku is an A8 star, but the calcium indicates A5 and the metallic lines F4, leading to its unusual spectral type kA5hA8mF4.

As elements heavier than hydrogen usually sink into the star over time due to gravity as the density of the core increases, it can generally be assumed that the metallicity of Solakku in its inner layers is even higher than what the photospheric composition would suggest.

Structure

Structurally, Solakku consist of several zones, separated by short transition layers. The main layers are the core, convective zone, radiative zone and atmosphere, which is itself split into the photosphere, chromosphere and corona.

Core

The core of Solakku makes up about 20% of its radius and is the only place inside the star where nuclear fusion is possible due to the immense pressures and temperatures, which are estimated to be as high as 21 million kelvin.

Fusion takes place through both the proton-proton chain as well as the CNO cycle. Both of these processes convert hydrogen into helium at a rate of 5.068×10¹² kg, of which 3.47×10¹⁰ kg/s (0.7%) are converted into energy and 7.095×10⁹ kg/s (0.0014%) are released as neutrinos, the mass of which is equal to roughly 2% of Solakku’s total energy output.

Convective zone

As the CNO cycle requires higher temperatures and produces more energy, it only occurs closer to the center of the core and produces more heat, while the proton-proton chain dominates the outer core, but produces less heat.

This, combined with the generally high energy output of the core, generates a temperature gradient which is steep enough to cause convection within the star, which extends up to 50% of Solakku’s radius. This process aids in heat transfer, moving energy away from the hot core and towards the upper layers of the star.

Radiative zone

Further away from the core, temperatures and pressures fall rapidly, away from what is required to sustain convection currents. The rapid change in density in particular is what ultimately makes convection impossible. The result is a layer which is in thermal equilibrium and posseses a much more gradual temperature gradient.

This layer extends up to the surface of Solakku and transfers energy passively through thermal conduction or radiative diffusion, the latter of which gives this layer its name. Energy is only moved slowly through these processes, arriving at the final, observable surface temperature of Solakku.

Atmosphere

The atmosphere of Solakku consists of a photosphere, chromosphere and corona. The photosphere is defined as the visible surface of the star, or the deepest layer that is no opaque to visible light. Thermal photons produced here are able to escape to become sunlight. This zone is usually several hundred to a few thousand kilometres thick, a tiny fraction of Solakku’s full radius.

The spectrum of the light emitted here can be approximated as that of a black-body radiating at 7803 K, the measured surface temperature of Solakku.

Particle densities drop of rapidly in the Chromosphere and Corona, though temperatures increase to over 20,000 K in the Chromosphere and millions of K in the Corona. It is possible to briefly observe the Corona once a day on Avalon, but only from the Valaya-facing side, when Solakku itself has just been eclipsed by the ice giant, with the Corona appearing as a fain white whisp trailing the star.

The radius of the Corona, and thus the Atmosphere as a whole, is variable from point to point, depending on speed and particle density of the solar winds making up the Corona, but can be up to 24 times the radius of Solakku, past the orbit of Infernum.

Solar radiation

Sunlight

Solakku mostly emits light of higher wavelengths due to its high temperature, leading to an apparent color of blue-tinged white. As well as providing visibility during daytime, this light is the primary energy source for life on Avalon, directly powering photosynthesis.

However, Solakku also radiates ultraviolet photons, which are attenuated by Avalon’s ozone layer. UV Radiation that reaches the surface can have positive biological effects, but higher wavelengths of it can be dangerous and can be considered mutagens in some contexts. These emissions are therefore directly responsible for a number of biological adaptions seen particularly in lower latitudes on Avalon, where light has a more direct path through the ozone layer.

The light energy emitted by Solakku equals a total output power of 3.125×10²⁷ watts, but due to the inverse-square law, only about 269.9 W/m² reaches Avalon. This value is known as the solar flux and represents the amount of energy reaching Avalon’s position. The exact amount that reaches the surface may be lower and depends on atmospheric factors and latitude, but also on the exact positions of Valaya and Avalon in their respective orbits.

Solar activity

TODO: section on solar activity, mainly flares

Life phases

Formation

Solakku formed approximately 2.6 billion years ago through gravitational collapse of a molecular cloud, beginning its life cycle. This occurred most likely at the same time as Crest’s formation, as they are projected to have very similar ages. However, Crest does not share Solakku’s chemical peculiarities, so the two stars may have formed in different regions of their molecular cloud. Another theory posits that Crest was captured by Solakku and the overlapping ages are merely a coincidence.

Main Sequence

TODO: mention age and how far it is into its main sequence

After hydrogen exhaustion

Location

TODO: section on location and celestial neighbourhood

Solar system

TODO: section on planetary system with relevant links to individual bodies

TODO: embed relevant links to wikipedia articles in text