A → close binary star lying at the center of the
→ supernova remnant W50, in → Aquila,
about 18,000 → light-years away.
The system consists of a normal → O star
or → B star in a 13.087 day orbit around a compact object
that is either a → neutron star or a
→ black hole. Material transferred from the normal star into
an → accretion disk surrounding the compact object
is ejected in two jets of ionized gas in opposite directions,
at about a quarter of the speed of light. The system is also a periodic X-ray source.
The jets are emitted in a cone with a half-angle of about 20°. The cone is inclined by
80° to the line of sight. The compact object precesses with a period of 164 days.
This causes the projected angle of the jets to go through a 164 day cycle, giving
the variation in the Doppler shifts.
See also: Such called because this object carries number 433 in the
Stephenson-Sanduleak catalog of stars with strong emission
lines, compiled by Bruce Stephenson and Nicholas Sanduleak in 1977.
