A Fast Low-Ionization Emission Region, or FLIER, is a volume of
gas with low
ionization, moving at
supersonic
Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...
speeds, near the symmetry axis of many
planetary nebulae. Their outflow speeds are significantly higher than the
nebulae in which they are embedded, and their ionizations are much lower. FLIERs' high speeds suggest ages much younger than their parent nebulae, and their low ionizations indicate that the
ultraviolet radiation that ionizes the gas around them does not penetrate into the FLIERs. The
Blinking Planetary
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 ...
features a set of FLIERs.
[Terzian, Yervant]
References
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Planetary nebulae