The region of space around the star Eta Carinae is a complex and turbulent area.
Against the wide backdrop of the Eta Carinae Nebula can be seen an expanding region of
dark gas - the 'Keyhole' of the Keyhole Nebula.
The Nebula consists of a huge cloud of ionised hydrogen
surrounding the extraordinary star Eta Carinae. Eta Carinae itself is a
binary system, consisting of two massive stars
in a mutual embrace, each casting off spherical shrouds of matter to form a peculiar dumb-bell shape.
It is one of the most massive and luminous stars known, and also one of the most
variable. In the mid-nineteenth century, it was one of the
brightest stars in the sky, but has now faded very considerably.
Surrounding the hourglass of Eta Carinae is an extensive cloud of ionised gas, within which
several star clusters are in the process of forming. Clouds of dark obscuring
dust swarm through the nebula, too, and the most prominent of these gives the
nebula its name. This is a vast and rapidly expanding dark cloud
in the central parts of the main nebula, that gives its common name of the 'Keyhole'.