A magnificent blue-white O star that is the third brightest star in the constellation Ophiuchus. Were it not so obscured by clouds of gas and dust (it even illuminates one of them and is well-known for its strong interstellar absorption lines), Zeta Oph would be one of the brightest stars in the sky. It is roughly midway through its 8-million-year lifetime that will end in a supernova explosion. Like most luminous stars, Zeta Oph is losing mass through a strong wind, blowing at about 1,600 km/s and carrying away about a hundredth of a millionth of a solar mass per year. It also one the sky's most famed runaway stars – stars that used to be together and are now fleeing from a once-common point. Zeta Ophiuchi seems to have been expelled from a binary system in the Scorpius-Centaurus Association when its one-time more-massive companion exploded. The explosions that make supernovae are apparently off-center, so that when one of the stars goes off and is blasted like a bullet to one side, the other one can, if conditions are right, be shot off as well. Zeta Ophiuchi is now single, however, so that the scene cannot repeat itself.
Visual magnitude
2.54
Absolute magnitude
-3.20
Spectral type
O9.5V
Surface temperature
32,500 K
Luminosity
68,000 Lsun
Radius
8 Rsun
Mass
20 Msun
Distance
458 light-years (140 pc)
Position
R.A. 16h 31m 39s,
Dec. -10° 21' 53"
Other designations
13 Oph, HR 6175, BD -10°4350, HD 149757, SAO 160006, FK5 622, HIP 81377
