SuWt 2 is a

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

viewed almost edge-on in the constellation of

Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...

. It is believed that high

UV radiation Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of t ...

from an undiscovered

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

ionizes this nebula. Currently, there is a

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

consisting of two

A-type main-sequence star An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

s whose radiation is not sufficient to photo-ionize the surrounding nebula. The nebula is easily obscured by the brighter star,

HD 121228 HD 121228 is a blue supergiant star located in the constellation Centaurus. The star is noted for its close visual proximity to the planetary nebula SuWt 2. References See also

*Zeta Persei - Same spectral class Henry Draper C ...

. It has been suggested that it has a triple stellar system. One of them, which is more massive than other two

s, evolved rapidly and became a

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

, swallowing the other two stars, and produced the planetary nebula.

References

Planetary nebulae Centaurus {{nebula-stub