A star (or "sun") is a massive energy-producing sphere of plasma and gas located in space. The region around a star that is held by its gravity, including any planets, moons, comets, and asteroids, is called a star system. A set of stars inside a field of view is called a starfield.
Stellar life cycle
Stars are born out of huge gaseous nebulae. Inside these nebulae, centers of higher density form, slowly accumulating more mass as the center's gravity increases, to form a protostar. Pressure in the interior of the protostar rises, in turn increasing the density and temperature until the gas turns to plasma, where the atomic nuclei and the electrons are dissociated from each other. At a sufficient temperature and pressure, nuclear fusion is initiated at the stellar core, producing light: the star is born.
Stars can be made up of various different elements depending on their age.
Young stars mainly consist of hydrogen, which is fused to helium thereby increasing the star's helium ratio over time and producing large quantities of energy. This energy, in turn, creates extreme pressure, preventing the star from collapsing under its own gravity.
- Dr. Tolian Soran used a trilithium weapon in 2371 to stop all fusion reactions inside the Amargosa sun, thereby collapsing the star and altering the gravitational conditions in the system. (Star Trek Generations)
As a sun gets older it begins to fuse heavier elements, like helium, as the lighter elements like hydrogen are depleted. This, however, releases more energy, causing the star to swell, which increases its surface area from which the energy is emitted. This phase marks the beginning of the star's end.
- In 2367, Dr. Timicin of the planet Kaelon II tried to save the dying star Kaelon by regulating its ever-increasing temperature with the bombardment of photon torpedoes. However, the experiment failed after testing the procedure with a star in an uninhabited solar system. (TNG: "Half a Life")
Because of its larger surface area, the star turns red and is then called a red giant. After the sun runs out of light elements and the number of fusion reactions decreases, its own gravity causes it to collapse and to expel its outer layers of matter, creating beautiful "planetary nebulae". The remnant of the star is called white dwarf.
Every star has to pass these stages of evolution. However, depending on their masses, some suns experience further changes.
Below 1.5 Sol masses: After one to ten billion years any nuclear reactions inside the white dwarf finally cease and the star turns to a "black dwarf", a very small stellar corpse.
- Planets orbiting stars going through this phase would often experience extreme temperature decreases, such as in the case of Psi 2000 and Exo III, which orbited black dwarves. (TOS: "The Naked Time", "What Are Little Girls Made Of?")
- In 2370, the USS Prometheus hosted Dr. Gideon Seyetik's successful attempt to re-ignite the stellar corpse Epsilon 119 by using a protomatter-laden shuttlepod remotely sent into the star. In the case of a failure, the star could have exploded in a supernova instead. (DS9: "Second Sight")
Above 1.5 Sol masses: The white dwarf swells again, fusing all elements up to iron. After the last iron is depleted, the star turns into a supernova, where the outer layers of the sun explode, which, in turn, causes a massive shock wave. The remains of this explosion are a vast matter nebula and a tiny neutron star, which is so dense, that all protons and electrons are neutralized to neutrons. A special form of neutron stars are pulsars.
- In 2269, the star Beta Niobe turned to a supernova, when crewmembers of the Federation starship USS Enterprise were almost trapped on its planet Sarpeidon. (TOS: "All Our Yesterdays")
- The resulting electromagnetic pulse from the supernova of Beta Magellan in 2364 was so feared by the computer-dependent Bynar in the nearby Beta Magellan system that they commandeered the USS Enterprise-D as a temporary dump for their planetary computer. (TNG: "11001001")
- In 2373, a series of supernovae witnessed by the USS Voyager in the Delta Quadrant turned out to be the real-time result of "battles" during a civil war in the Q Continuum. They were actually created by spatial disruptions in the Continuum, which created a negative-density false vacuum that sucked nearby matter into the Continuum. (VOY: "The Q and the Grey")
- In 2387, the Romulan sun went supernova and destroyed Romulus. Although this was known at least two years in advance, the planet's evacuation could not be completed in time. (Star Trek; PIC: "Remembrance")
If the remnant of a supernova is more massive than 2.5 Sol masses, it collapses to a black hole.
Stars are assigned to different spectral classes.
- F-type star
- G-type star
- Neutron star
- O-type star
- Red dwarf
- Red giant
- T-Tauri type
- White dwarf
- Yellow dwarf
- Black hole
- Black star