The system's combined apparent visual magnitude of 0.61 makes it the second-brightest object in Centaurus and the eleventh brightest star in the night sky.

Hadar comes from the Arabic حضار (the root's meaning is "to be present" or "on the ground" or "settled, civilized area"[10]), while the name Agena /əˈdʒiːnə/ is thought to be derived from the Latin genua, meaning "knees", from the star's position on the left knee of the centaur depicted in the constellation Centaurus.

[13] The Boorong people indigenous to what is now northwestern Victoria, Australia named it Bermbermgle (together with α Centauri),[14] two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" (Coalsack Nebula).

[16] Because of its spectral type and the detection of pulsations, the Aa component has been classified as a β Cephei variable.

The companion is separated from the primary by 1.3 seconds of arc, and has remained so since the discovery, although the position angle has changed six degrees since.

Component Ab, the slow-rotating star, has a strong magnetic field although no detected abundance peculiarities in its spectrum.

Multiple pulsations modes have been detected in component Aa, some of which correspond to brightness variations, so this star is considered to be variable.