Definitions

CRL 2688

Egg Nebula

The Egg Nebula (also known as RAFGL 2688 and CRL 2688) is a bipolar protoplanetary nebula approximately 3,000 light-years away from Earth. It was discovered by Raghvendra Sahai and John Trauger of NASA's Jet Propulsion Laboratory in Pasadena, California. RAFGL 2688 press release was distributed on January 16, 1996.

The Egg Nebula's defining feature is the series of bright arcs and circles surrounding the central star. A dense layer of gas and dusts enshrouds the central star, blocking its direct light from our view. However, the light from the central star penetrates the thinner regions of this dusty enclosure, illuminating the outer layers of gas to create the arcs seen in this resplendent image (Hubble Site).

The dusty enclosure around the central star is very likely a disc. The bipolar outflows in the image indicate that the system has angular momentum, which is very likely generated by an accretion disc. In addition, a disc geometry would account for the varying thickness of the enclosure that allows light to escape along the disc's axis and illuminate the outer layers of gas, but still blocks it from our direct view along the disc edge. Although dusty discs have been confirmed around several post-AGB objects (S. De Ruyter et. al, 2006), a disc around the Egg Nebula is yet to be confirmed.

The Egg Nebula was photographed by the Wide Field and Planetary Camera 2 of the NASA/ESA Hubble Space Telescope.

Notes

  1. distance × sin (diameter_angle / 2 ) = 0.2 ly. radius
  2. 14.0 apparent magnitude - 5 * (log10(920 pc distance) - 1) = 4.2 absolute magnitude

References

  1. Hubble Finds Searchlight Beams and Multiple Arcs around a Dying Star STScI Press release: Space Telescope Science Institute. January 16, 1996.
  2. De Ruyter et al. Keplerian discs around post-AGB objects: a common phenomenon? Astronomy & Astrophysics 448, 641–653 (2006).

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