Stars

Galaxies are made up of billions of stars. It is estimated that the Milky Way contains 100-400 billion stars. Stars form the center of star systems, orbited by planets, asteroids, and more. Sol, our sun, is one such star; its closest stellar neighbor is Proxima Centauri, some 4 light years away.

The universe is teeming with life, sometimes in the most unlikely places. Of carbon-based human-like advanced life, larger stars (O, B, A) do not typically last long enough for advanced life to develop, while smaller stars (M) tend to tidally lock their planets making them generally uninhabitable. The most probable stars for human-like life have been found to be mainsequence stars between types A and M – most commonly dwarf stars of types F, G, and K.

It should be noted, though, that life doesn’t have to develop in a star system to be present. Populations migrate, terraforming and other colonization techniques exist, and outposts and space stations can substitute for planets. Additionally, planets can have enough geothermal heating to make subterranean life that never sees the surface possible. While life around a slow pulsar or similar stellar object might be unusual, life finds a way to thrive anywhere.

Spectral Classification

Stars are classified based on their temperature. The classification system, originally devised in the 20th Century by Morgan and Keenan uses a system of letters and numbers. The letters indicate a broad spectral classification, with numbers subdividing them further.

Type Description Examples

O (blue) Hot, extremely luminous Tau Canis Majoris, Lambda Cephel

B (blue-white) Luminous Rigel, Bellatrix, Spica

A (white) Common Sirius, Deneb, Altair, Fomalhaut

F (yellow-white) Common Alkrakis, Canopus, Polaris

G (yellow) Common Sol, Alpha Centauri A, Tau Ceti

K (orange) Common Aloha Centauri B, Epsilon Eridani, Artcurus, Aldeberan

M (red) Most common; red dwarfs and red giants Betelgeuse, Antares, Prixima Centauri, Barnard's Star

Luminosity Class

Additionally, a luminosity class is represented by Roman numerals. Sol, for example, is a G2V star – a yellow main sequence star with a temperature of about 5,800K.

Luminosity Description

I Supergiant

II Bright giant

III Giant

IV Sub-giant

V Main-sequence or Dwarf

VI Sub-dwarf

Unusual Stars

There are some additional stellar classifications which do not fit into the standard system of classification.

Type Description Examples

W Dying supergiants Gamms Velorum A

L Red dwarfs, faint; some supergiants V838 Monocerotis

T Methane dwarfs; cool brown Epsilon Indi Ba

Y Ultra-cool brown dwarfs WISE 0410+1502

C Carbon stars; ancient red giants R Cmi, R Leporis

S Giants and supergiants S Ursae Majoris

D White dwarfs (“degenerate”) Sirius B, Van Maanen’s Star

Neutron Stars

After a massive supernova, the remnants can form a neutron star. Very hot and very small (about the size of a town), neutron stars have such a high density that a teaspoon of matter can weigh as much as a 21st century aircraft carrier. Neutron stars tend to spin very fast, and have an escape velocity of about one-third the speed of light. Some neutron stars which direct radio waves, X rays, or gamma radiation at regular intervals are known as pulsars, while those with immensely strong magnetic fields are called magnetars. Different pulsars have different pulse intervals, ranging from milliseconds up to several seconds.

A star system - including the surfaces of planets - around a neutron star is highly radioactive, with high energy cosmic rays which can seriously harm living creatures and cause radiation sickness, although some protection can be found below the planet’s surface. An unprotected person takes 1d6 radiation damage per hour, and a starship without shielding takes 1d6 crew casualties per day or part thereof.

Magnetars additionally disturb sensor or scanner readings, inflicting a -2d6 penalty to them, as well as to any space navigation checks.