ζ Ophiuchi is an enormous star with more than 20 times the
Sun's mass and eight times its
radius. The
stellar classification of this star is
O9.5 V, with the
luminosity class of V indicating that it is generating energy in its core by the
nuclear fusion of hydrogen. From Earth, the apparent
effective temperature of the star appears to be 34,300K, giving the star the blue hue of an
O-type star. However, since the star is rapidly rotating, the exact surface temperature varies across the surface of the star from as high as 39,000K at the poles to as low as 30,700K at the equator. The
projected rotational velocity may be as high as and it may be rotating at a rate of once per day, close to the velocity at which it would begin to break up. for Zeta Ophiuchi, adapted from Howarth
et al. (2014) This is a young star with an age of at least six million years. Its luminosity is varying in a periodic manner similar to that of a
Beta Cephei variable. This periodicity has a dozen or more frequencies ranging between 1–10 cycles per day. In 1979, examination of the spectrum of this star found "moving bumps" in its helium line profiles. This feature has since been found in other stars, which have come to be called ζ Oph stars. These spectral properties are likely the result of non-radial pulsations. This star is roughly halfway through the initial phase of its
stellar evolution and will, within the next few million years, expand into a red
supergiant star wider than the orbit of
Jupiter before ending its life in a
supernova explosion, leaving behind a
neutron star or
pulsar. From the Earth, a significant fraction of the light from this star is absorbed by interstellar dust, particularly at the blue end of the spectrum. In fact, were it not for this dust, ζ Ophiuchi would shine several times brighter and be among the very brightest stars visible. If the star's luminosity were not obscured, it would shine at magnitude 1.54, becoming the brightest of the constellation and the
twenty-third brightest star in the night sky. X-ray emissions have been detected from Zeta Ophiuchi that vary periodically. The net X-ray flux is estimated at . In the energy range of 0.5–10
keV, this flux varies by about 20% over a period of 0.77 days. This behavior may be the result of a magnetic field in the star. The measured average strength of the longitudinal field is about . ==Bow shock==