Procyon B is a dim white dwarf star. A white dwarf is a stellar remnant composed mostly of electron-degenerate matter.
Procyon B is difficult to observe, as it has a visual magnitude of only 10.82 (15,000 times fainter than Procyon A), lying at just 5 seconds of arc from its primary, Procyon A.
Procyon B is only 0.0006 as luminous as our Sun, and only 0.02 its diameter (half the size of Earth). Because it is a white dwarf, it still has 0.6 of our Sun’s mass, having a density estimated to be around 0.33 tonne per cubic centimeter.
Procyon B is separated from Procyon A by an average of only 14.9 au – roughly the distance between Uranus and , though the eccentric orbit carries them as close as 8.9 au and as far as 21.0 au. The two components orbit each other with a period of 40.8 years.
With a surface temperature of 7,740 K deduced from its spectrum, Procyon B provides evidence of its lesser mass and greater age.
Procyon B is the degenerate remnant of what was once a much larger, brighter and hotter star that eventually shed its outer envelope to leave behind the compact carbon-helium core.