Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 astronomical units (3.0×109 km; 1.9×109 mi) (roughly the distance between the Sun and Uranus) and a period of 50.1 years.
The brighter component, termed Sirius A, is a main-sequence star of spectral type A1V, with an estimated surface temperature of 9,940 K. Sirius A has a mass double that of the Sun. The radius of this star has been measured by an astronomical interferometer, giving an estimated angular diameter of 5.936±0.016 mas. The projected rotational velocity is a relatively low 16 km/s, which does not produce any significant flattening of its disk. This is at marked variance with the similar-sized Vega, which rotates at a much faster 274 km/s and bulges prominently around its equator. A weak magnetic field has been detected on the surface of Sirius A.
Sirius B is a star that has already evolved off the main sequence and become a white dwarf.Currently 10,000 times less luminous in the visual spectrum, Sirius B was once the more massive of the two. The age of the system has been estimated at around 230 million years. Early in its lifespan it was thought to have been two bluish white stars orbiting each other in an elliptical orbit every 9.1 years. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.
With a mass nearly equal to the Sun's, Sirius B is one of the more massive white dwarfs known (0.98 solar masses); it is almost double the 0.5–0.6 solar-mass average. Yet that same mass is packed into a volume roughly equal to the Earth's. The current surface temperature is 25,200 K. However, since there is no internal heat source, Sirius B will steadily cool as the remaining heat is radiated into space over a period of more than two billion years.
The Sirius system emits a higher than expected level of infrared radiation, as measured by IRAS space-based observatory. This may be an indication of dust in the system, and is considered somewhat unusual for a binary star.
In Space Opera
- The Borderland of Sol (1975), Known Space short story by Larry Niven published in the collection Tales of Known Space? (1975). Jinx is a massive moon of the gas giant Primary in orbit around Sirius A
- The Sirian Experiments? (1980), third novel in the Canopus in Argos? series by Doris Lessing?.
- Mudd's Passion? (1973), episode of Star Trek: The Animated Series? written by Stephen Kandel? and directed by Hal Sutherland?, as part of the film, television, and print franchise originated by Gene Roddenberry?. In 2269, the planetary government of Sirius IX? charges Federation outlaw Harry Mudd with fraud and swindling, to wit, selling fake love-crystals.
- Frontier in Space? (1973), serial of the British television series Doctor Who?, written by Malcolm Hulke? and directed by Paul Bernard?. The Doctor and his companion Jo Grant are the victims of an elaborate frame-up as career criminals. Who's old nemesis, the Master, poses as an official from the Dominion government of the semi-autonomous Earth colony Sirius IV?, and he brings "proof" of The Doctor's origin in the Sirian system and his incontrovertible guilt.
- The Caves of Androzani? (1984), serial of the British television series Doctor Who, written by Robert Holmes? and directed by Graeme Harper?. The colonized planets Androzani Major? and Androzani Minor? are in the Sirius system.
- Traveller? (1977), role-playing game designed by Marc Miller? and published by GDW. The Sirius system is barren of planets, swept clean by the searing radiation and intense stellar wind of its dominant star Sirius A.
- Frontier: Elite II? (1993) and Frontier: First Encounters? (1995), computer games written by David Braben? et al. The Sirius system is the location of the headquarters of the Sirius Corporation?.
- Escape Velocity, computer game by Ambrosia Software has on station, Sirius Station, and one planet, Sirius III, in the system.