Luyten 726-8 A
Star
Luyten 726-8 A (BL Ceti) — the brighter of a close pair of tiny red dwarfs 8.7 light-years away in Cetus. Like its twin it is a flare star, prone to sudden magnetic outbursts. The two stars, each barely a tenth of the Sun's mass, orbit each other about every 26 years.
Open in 3D viewSee Luyten 726-8 A in the live, interactive 3D map
Key facts
Mutual orbit
26.3 Earth years
9,599 Earth days
Mass
2.44 × 10²⁹ kg
0.122 M☉
Radius
114,790 km
16% of the Sun's radius
Surface temperature
2,720 K (2,447 °C)
Luminosity
4.98 × 10²³ W
Spectral type
M5.5V (red dwarf; variable BL Ceti)
Science
Physical
- Mass
- 2.44 × 10²⁹ kg · 0.122 M☉
- Radius
- 114,790 km · 16% of the Sun's radius
- Density
- 38,454 kg/m³ · 38× water
- Computed from mass and radius
- Spectral type
- M5.5V (red dwarf; variable BL Ceti)
Motion through space
- Note
- The motion of the pair's common centre of mass, computed as the mass-weighted mean of its stars' catalogued motions.
- Proper motion
- 3.33 arcseconds per year · its drift across our sky
- SIMBAD — 2020yCat.1350....0G
- Radial velocity
- +20.9 km/s · moving away from the Sun
- SIMBAD — 2020yCat.1350....0G
- Speed across our line of sight
- 42.6 km/s
- Computed from proper motion and parallax
- Speed through space, relative to the Sun
- 47.4 km/s
- Computed from proper motion, parallax and radial velocity
Orbit (around the system barycenter)
- Semi-major axis
- 2.76 AU
- From the interferometric orbit of Kervella et al. 2016 (P = 26.3 yr, a = 5.6 AU, e = 0.62)
- Eccentricity
- 0.617
- From the interferometric orbit of Kervella et al. 2016 (P = 26.3 yr, a = 5.6 AU, e = 0.62)
- Orbital period
- 26.28 years
- From the interferometric orbit of Kervella et al. 2016 (P = 26.3 yr, a = 5.6 AU, e = 0.62)
Composition
- By mass
- A tiny hydrogen/helium red dwarf near the low-mass end of the main sequence (~0.12 M☉, ~2720 K). Like its twin it flares — sudden magnetic outbursts brighten it for minutes at a time.
Temperature
- Surface
- 2,720 K (2,447 °C)
Radiation & temperature
- Luminosity
- 4.98 × 10²³ W · 0.0013 L☉
- Surface temperature
- 2,720 K (2,447 °C)
- Peak wavelength
- 1065 nm · near-infrared (mostly invisible to the eye)
- Computed (Wien's law) from the surface temperature
Discovery & history
- Discovered
- 1948
- By
- Willem Jacob Luyten
- Method
- Telescope
- Name
- Named for the astronomer Willem Luyten and its survey number; the components carry the variable-star names BL Ceti (A) and UV Ceti (B).
Discovered by Willem Luyten in 1948 during his proper-motion survey — the 726-8 entry — and quickly found to be a close double whose fainter component is the archetypal flare star UV Ceti. No planets are confirmed around either.
Images
Images from open archives · credit shown per image