NGC 6826 (also known as Caldwell 15) is a
planetary nebula located in the constellation Cygnus. It is
commonly referred to as the "blinking planetary", although many
other nebulae exhibit such "blinking". When viewed through a
small telescope, the brightness of the central star overwhelms
the eye when viewed directly, obscuring the surrounding nebula.
However, it can be viewed well in the peripheral vision (averted
vision), which causes it to "blink" in and out of view as the
observer's eye wanders. A distinctive feature of this nebula are
the two bright patches on either side, which are known as FLIERs,
or Fast Low-Ionization Emission Regions. They appear to be
relatively young, moving outwards at supersonic speeds.
According to Bruce Balick (University of Washington), "some of
their observed characteristics suggest that they are like sparks
flung outward from the central star late in the very recent past
(a thousand years ago). Yet their shapes ... seem to suggest
that they are stationary, and that material ejected from the
star flows past them, scraping gas from their surfaces. Future
Hubble observations will monitor any changes in the positions of
FLIERs to resolve this issue. In either case, the formation of
FLIERs cannot be easily explained by any models of stellar
evolution."
