Types of Stars

This page lists the types of stars in the Milky Way.

* Black Dwarf: A dead star, having radiated all its heat.
* Black Hole: The singularity which results from the death of a supermassive star more than 20 Sol masses.
* Brown Dwarf: A failed star, resembling a gas giant. Little or no nuclear fusion. 0.013-0.08 Sol masses (13 to 75 Jupiter masses). 20% chance of binary system with a low mass star.
* Main Sequence Star: The majority of stars are main sequence stars with masses 0.1-200 Sol Masses. Within main sequence stars, hydrogen is converted to helium. Categorized as O, B, A, F, G, K, M by mass, with O being the most massive and M being the least massive.
* Neutron Star: The core of a dead supermassive star.
* Protostar: A star in its earliest stages
* Pulsar: A neutron star which releases charged particles.
* Red Giant: An unstable star in its late stages
* Supermassive Star: A massive, short-lived star formed from massive protostars. Create a supernova when exploded.
* White Dwarf: Post red giant star. Relatively stable. Very dense.

## Considerations for World Building

### Orbits

* Planetary orbits can be determined by multiplying the orbit of a gas giant by 1.42<x<2.00 (for outer planets) and dividing by 1.42<x<2.00 (for inner planets)
* No orbit may be closer than 0.15 AU

### Stellar Lifespans

* O, B and A type stars have lifespans of a few million years

### Stellar Habitability

* Planets within the habitable zone of an M type star will face considerable solar weather
* Large F stars and G, K and M stars release plentiful UV light, resulting in reduced atmosphere within the habitability zone
* Binary Stars result in planets have unstable orbits

### Galactic Habitability

* Planets in the galactic bulge will have unstable orbits and will be exposed to massive amounts of radiation due to close proximity to the galactic core
* Planets within a galactic arm will be drenched in radiation and may be torn apart
* Optimal planet-forming area is in the galactic disk between arms
* Systems further from the galactic core will have less heavy elements

### Binary Systems

#### Close Systems

* Star separation, in order to facilitate planet formation, should be between 0.15-6 AU (tends towards lower value)
* Average distance from primary star to barrycentre (b) = separation of stars x (Msecondary/Mprimary+Msecondary)
* Eccentricity (e) between 0.4 and 0.7 (tending towards the lower value)
* Max Distance from barrycentre = b(1+e)
* Min Distance from barrycentre = b(1-e)
* Overall maximum (MaxO) = Max(Primary) + Max(Secondary)
* Overall minimum (MinO) = Min(Primary) + Min(Secondary) : this value must not be >0.1 AU
* Forbidden zone (where no planets form) is between 1/3MinO (inner) and 3MinO (outer)
* Habitable world must exist beyond 4MaxO AU

#### Far Systems

* Star separation should be between 120-600 AU (tending towards the larger)
* Barrycentre, Eccentricity and Max/Min as in close systems
* Inner Planetary Limit  *(I) = 0.1 x M*
* Outer Planetary Limit *(O) = 40 x M*
* Forbidden zone should fall outside outer limit

### Multiple-Star Systems

* Stars are grouped into subsystems of 1 or 2 stars
* Primary star is most massive, which each subsequent star lesser in mass
* Overall mass of primary subsystem must be greater than the other subsystems
* Average separation is between 1200 AU and 60 000 AU
* Barrycentre, Eccentricity and Max/Min as in close systems

## Star Statistics

* Luminosity *(L) = M^3* where M is equal to mass (1M = 1 Sol Mass)
* Diameter *(D) = M^0.74* (1D = 1 Sol Diameter)
* Surface Temperature *(T) = M^0.505* (1T = 1 Sol Temperature)
* Lifespan *(V) = M^-2.5* (1V = 1 Sol Life)
* Habitability Zone *(H) = sqrtL x 0.95* (min) and *sqrtL x 1.37* (max) (1H = 1AU)
* Inner Planetary Limit  *(I) = 0.1 x M*
* Outer Planetary Limit *(O) = 40 x M*
* Frost Line *(F) = 4.85 x sqrtL*
* Apparent Brightness (AB) = L/D^2
* Apparent Brightness of a planet = Albedo x L(radius of planet being observed)^2/D^2 x d^2 (where D is the distance from the planet of observance to the star and d is the distance from the planet of observance to the planet being observed). Greater than 1.3x10^-7 may be observed by the naked eye, and less than 1.2x10^-9 may not.
* Small angle approximation ($) = d/D (where d is the diameter of the object being observed and D is the distance between the object and the observer). $(Sol) = 0.5 degrees