Procyon B

Star

Procyon B — a white dwarf, the burnt-out core of a once-larger star, and the faint companion of brilliant Procyon A. It packs about 0.6 solar mass into a ball roughly the size of Earth (radius ~8,600 km), making it extraordinarily dense. Its surface is ~7,700 K — hot, though cooler than Sirius B — and it simply radiates stored heat as it cools. No white dwarf's surface has ever been imaged.

Open in 3D viewSee Procyon B in the live, interactive 3D map

Key facts

Mutual orbit

40.8 Earth years

14,917 Earth days

Mass

1.18 × 10³⁰ kg

0.592 M☉

Radius

8,585 km

1% of the Sun's radius

Surface temperature

7,740 K (7,467 °C)

Luminosity

1.88 × 10²³ W

Spectral type

DQZ (white dwarf with traces of carbon and metals)

Science

Physical

Mass: 1.18 × 10³⁰ kg · 0.592 M☉
Radius: 8,585 km · 1% of the Sun's radius
Density: 444,261,750 kg/m³ · 4.4e+05× water; Computed from mass and radius
Spectral type: DQZ (white dwarf with traces of carbon and metals)

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: 1.26 arcseconds per year · its drift across our sky; SIMBAD — 2007A&A...474..653V, 2001AJ....121.2189O
Radial velocity: -4.5 km/s · approaching the Sun; SIMBAD — 2007A&A...474..653V, 2001AJ....121.2189O
Speed across our line of sight: 20.9 km/s; Computed from proper motion and parallax
Speed through space, relative to the Sun: 21.4 km/s; Computed from proper motion, parallax and radial velocity

Orbit (around the system barycenter)

Semi-major axis: 10.7 AU; From the visual-binary orbit of Bond et al. 2015 (P = 40.84 yr, a = 15 AU, e = 0.41)
Eccentricity: 0.407; From the visual-binary orbit of Bond et al. 2015 (P = 40.84 yr, a = 15 AU, e = 0.41)
Orbital period: 40.84 years; From the visual-binary orbit of Bond et al. 2015 (P = 40.84 yr, a = 15 AU, e = 0.41)

Composition

By mass: A white dwarf — the exposed, burnt-out core left when a star more massive than Procyon A shed its outer layers roughly 1.4 billion years ago. It packs about 0.6 solar mass into a ball roughly Earth's size (radius ~8,600 km), so it is enormously dense (see Physical, computed from the measured mass and radius). No fusion burns inside; held up by quantum degeneracy pressure, it simply radiates stored heat — ~7,700 K at the surface, cooler than Sirius B — and cools over billions of years. Its surface, like that of every white dwarf, has never been imaged.

Temperature

Surface: 7,740 K (7,467 °C)

Radiation & temperature

Luminosity: 1.88 × 10²³ W · 0.00049 L☉
Surface temperature: 7,740 K (7,467 °C)
Peak wavelength: 374 nm · ultraviolet (invisible to the eye); Computed (Wien's law) from the surface temperature

Discovery & history

Discovered: 1896
By: John Martin Schaeberle
Method: Telescope
Name: 'Procyon B' marks it as the faint companion of Procyon A.

Predicted by Friedrich Bessel in 1844 from Procyon's unexplained wobble, and first seen in 1896 by John Martin Schaeberle with the 36-inch Lick refractor. Its high mass and Earth-like size confirmed it as a white dwarf — a preview, like Sirius B, of the fate awaiting Sun-like stars.

Images

Where to find it — in Canis Minor, the Lesser Dog (IAU constellation chart). It is an unresolved point of light; its surface has never been imaged. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image