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Star
2022-02-06-m-dwarf
Image from Trolligi
Most stars in the universe today are red dwarfs, cold, dim, low mass, and extremely long-lived stars.

Stars are celestial bodies which are sufficiently massive to naturally achieve a significant rate of nuclear fusion of hydrogen to helium in their interior at some point in their lives. The majority of stars are composed mostly of hydrogen and helium, the two most abundant elements in the universe, although there are exceptions, such as Wolf-Rayet stars or white dwarfs.

Table of Contents

1. Structure and dynamics
1.1 Structure
1.2 Dynamics
2. Classification
3. Variability
4. Evolution
5. Star systems
6. Uses
6.1 Light
6.2 Materials
6.3 Archailect uses
6.4 Weapons
7. Modification
8. Cultural significance

Structure and dynamics

Structure

At the center of a star lies the core, where temperature and pressure are the greatest. In main sequence stars, this is the region where hydrogen fusion happens by either the proton-proton chain, which dominates in less massive stars, or the carbon-nitrogen-oxygen (CNO) cycle, which dominates in more massive stars. Helium ash builds up within this region as the star ages, eventually causing it to become nearly hydrogen-free by the end of the main sequence phase. In more massive stars, the core may continue fusing helium and heavier elements up to iron.

Energy produced by fusion at the center of the star is transported to the surface via two methods: radiation and convection. This manifests as the radiation zone, where energy is transported via radiation and conduction, and the convection zone, where energy is transported via convection. The placement and thickness of both zones differ depending on stellar mass and the current stage in stellar evolution, and affects the dynamics of the star. For example, main sequence stars less massive than roughly 7E29 kg (0.35 solar masses) are fully convective. This means, among other things, that nearly all hydrogen present within the star can enter the core and become fused over its lifetime.

Once energy produced at the core reaches the photosphere, the layer where the star becomes transparent and generally regarded as the lowest layer of the stellar atmosphere, it is finally emitted as radiation. Additionally, cooler stars containing sufficiently deep surface convection zones have two additional layers of atmosphere: the chromosphere and the corona.

Dynamics

Two main types of stellar magnetic fields play a dominant role in the dynamics of a star. Hotter stars with thin or nonexistent surface convection zones usually possess simple, stable, and dipolar fields. Cooler stars possessing deep surface convection zones generally have complex and dynamic fields, resulting in various phenomena within the stellar atmosphere. In the photosphere, granules (convection cells of plasma), faculae (bright valleys between granules), and starspots (dark or bright spots) can be observed, while spicules (short-lived vertical jets of plasma) and plages (bright regions analogous to faculae) may be found in the chromosphere. Additional phenomena include flares (bursts of light emission), prominences (large plasma and magnetic structures extending from the surface), and coronal mass ejections (ejection of stellar mass).

Stars emit a constant stream of particles known as the stellar wind. The strength of the stellar wind varies from star to star, and in extreme cases can lead to mass loss on the order of 1E30 kg over millions of years or less, as happens in extremely massive stars or post-asymptotic giant branch (post-AGB) stars. The stellar wind pushes back the interstellar medium, forming a bubble surrounding the star that is known as the astrosphere. The boundary separating the astrosphere from interstellar space, where the stellar wind collides with the interstellar medium, is the astropause.

  • Classification
  • Variability
  • Evolution

Uses

Stars are of immense utility to Terragen civilization. They are some of the most massive singular objects that can be found in the universe, and together they contain a large fraction of all mass-energy available in the Terragen Sphere. The two primary uses of stars are as sources of light and materials.

Light

Stars passively generate energy in the form of light that can be utilized even by simple beings, and is the primary source of energy for many biospheres, natural or artificial, directly or indirectly. Early Terragens on Earth were dependent on their home star, Sol, to survive, and this is also the case for many low technology cultures across the Terragen Sphere. While the development of nuclear fission, fusion and conversion reactors rendered illumination from stellar objects redundant long ago, many Terragens today still prefer to rely on sunlight and starlight to power themselves, their technologies, and their environments.

Dyson swarm and dyson sphere Megastructure that envelops the star for the purpose of capturing a large portion or all of the available radiation for use.
Matrioshka brain A high efficiency dyson swarm used for computation.
Light sails and statites Sheets of material, usually highly reflective, exploiting the momentum of photons to propel vessels in the case of light sails, or hold position above a star in the case of statites.
Starbooster Two statite swarms which reflect light emitted in off-plane directions back towards the star, causing its outer layers to become hotter and brighter.
Artisuns and sunlines Testaments to Terragens' fascination with sunlight. While they do not make direct use of stars, these are devices used to simulate natural sunlight.

Materials

Aside from light and warmth, stars are also useful as sources of materials. Most stars primarily consist of hydrogen and helium, with heavier elements (collectively referred to as metals) making up just a small fraction of the total. However, due to their high mass, stars often contain the vast majority of the heavier elements in a system. Although small-scale harvesting and usage of mass via stellar wind became possible early in Terragen history, large-scale utilization of stellar resources involving direct extraction of matter from the star itself is more difficult due to the extreme temperatures and gravity found around stellar objects. Therefore, stars were rarely used for materials until the third millennium when the development of more durable hardware, improved methods, and Deep Well Industrial Zones combined to make the practice much more common.

Stellar wind sails A mesh producing an electric or magnetic field that deflects charged particles in the stellar wind to produce thrust.
Stellar wind capture Harvesting of stellar wind materials. Usually employed by in-system cloudharvesters.
Star lifting Bulk removal of matter from stars. May be used for resource extraction purposes or for stellar husbandry.

Archailect uses

Stars appeal to the greatest minds of the Terragen Sphere, who require a large amount of mass-energy to operate; it is no surprise that the archailects often seek to claim the larger stars and connect them to the Wormhole Nexus. Complete disassembly of stars is commonly performed by archailects, who often convert them and their accompanying planetary systems into artifacts such as computation nodes, industrial machinery or weapons. Some archailects may also inhabit very large stars, converting them into Godstars.

Matrioshka hypernodes Advanced Matrioshka brain built and powered using the disassembled mass of an entire star.
Godstars A star converted into a computation node which can house one or more archailects.

Weapons

Stars are rich in mass and energy, which means they can be used to create immensely powerful weaponry for dealing with great threats. Fortunately, however, their great destructive potential means such weapons are rarely ever utilized.

Nicoll-Dyson beams Powerful laser beams emitted by dyson spheres. While normally used for propulsion and communication, they can also be used as weapons.
Conversion weapons Monopole-based self-replicating weapons sometimes used to detonate stars.

Modification

Intentional modification of stellar properties is known as stellar engineering. Stellar engineering can be divided into two types: star lifting and stellar husbandry. In addition to the modification of their physical properties, their kinematic properties can also be altered by stellar propulsion systems.

A related technology are stellification engines, which are used on non-stellar objects, especially jovian planets and brown dwarfs, to convert them into star-like objects.

Cultural significance

In addition to tangible usage, stars are also featured prominently in Terragen cultures. Many low tech cultures on Earth used stars for various purposes, such as timekeeping and navigation. Many cultures gave the brightest stars visible to them proper names, associated them with mythological figures and objects, and grouped them into asterisms and constellations. Various religions and metaphysical beliefs such as astrology also revolve around stars.

As more information regarding stars became available, their roles in Terragen cultures transformed from people and items into locations, usually simply serving as narrative anchors for the planets around them, where most stories took place. But many old traditions have survived and see continued usage. Many ancient star names have become widely used. Constellations from antiquity were codified and would later serve as ways to specify direction, and eventually, volumes of space as Terragens became an interstellar civilisation.

 
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Development Notes
Text by The Astronomer 2023
From an original article by M. Alan Kazlev.
Initially published on 31 December 2001.

Article overhaul phase 1 (2023-02-05, by The Astronomer)
 
 
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