The nebula has a very young white dwarf at its center, but this central white dwarf is peculiar. The Helix Nebula is an old planetary nebula – expanding, glowing gas ejected from its host star after its main-sequence life ended. A Process of Elimination, and a Disruptive Origin These observations provide one potential explanation for the fate of these planetary remains. In a paper published recently in The Astronomical Journal, researchers used new data from the Stratospheric Observatory for Infrared Astronomy ( SOFIA) and the Atacama Large Millimeter/submillimeter Array ( ALMA), as well as archival data from the Spitzer Space Telescope and the Herschel Space Observatory, to study the Helix Nebula. Astronomers generally don’t know what happens to planets beyond this point, or whether they can even survive. Once a star evolves beyond the main sequence – the longest stage of stellar evolution, during which the radiation generated by nuclear fusion in a star’s core is balanced by gravitation – the fate of any planetary system it may have had is an enigma. Models of the white dwarf photosphere (solid) and IR excess showing good fits to the data detections (circles) and upper limits (triangles). The plot combines optical, infrared, and millimeter photometry, the Spitzer mid-infrared spectrum, and upper limits from WISE, Spitzer, SOFIA, Herschel, and ALMA.

The spectral energy distribution of WD 2226-210 superposed on an image of the Helix Nebula from Hubble Space Telescope.

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