ZETA OPH (Zeta Ophiuchi). Just over the line into third magnitude
(2.56), and third brightest star within the constellation Ophiuchus (the Serpent Bearer), Zeta
Ophiuchi is oddly not graced with a proper name, which is odder
still since it is in the middle of the line of stars that make the
bottom border of the constellation, the others, from west to east
being Yed Prior (Delta Ophiuchi),
Yed Posterior (Epsilon), and Sabik (Eta) (though Zeta has been known
to share that name with just-barely-brighter Eta). Too bad too, as
Zeta Oph is truly the magnificent star, a blue-white class O
(though at 09.5 just barely) hydrogen-fusing "dwarf" (a strange
term for a star with a diameter 8 times that of the Sun). The star
(which is very slightly variable), however, does not LOOK so blue-
white. Zeta Oph is one of the brighter stars in the sky to be
significantly affected by absorption and reddening of its light by
passage through interstellar dust (which lies everywhere within the
Milky Way). At a distance of 460 light years, the star is deeply
involved with dust gas clouds (and even illuminates one of them),
and is used as a background light source with which to examine the
stuff of interstellar space. If the dust were not in the way, Zeta
would shine at almost first magnitude. From its distance and great
temperature of 32,500 Kelvin (from which we can account for the
star's fierce ultraviolet light), we calculate a magnificent
luminosity of 68,000 times that of the Sun, and from that a mass of 20 times
solar, the star about in the middle of its short (8 million years)
hydrogen-fusing lifetime. Like most luminous stars, Zeta Oph is
losing mass through a strong wind that in this case blows at about
1600 kilometers per second at a rate of about a hundredth of a
millionth of a solar mass per year. The star's only fate seems to
blow up as a supernova. Among Zeta Ophiuchi's most interesting
properties is that it is one of the sky's most famed "runaway
stars," stars that used to be together and are now fleeing from a
once-common point. The prime examples are Mu Columbae and AE
Aurigae, which are running away from Na'ir al Saif (Iota Orionis) after
an exchange and expulsion when two massive double stars encountered
each other. Zeta Ophiuchi, on the other hand, seems to have been
expelled from a double star system when its one-time and clearly
more-massive companion exploded and is now a tiny "neutron star"
about the size of a small town. 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.