These tadpole‐like structures have been found in the Helix nebula, the closest planetary nebula to Earth—450 light‐years away. With the aid of Wide Field Planetary Camera 2 on the Hubble Space Telescope, C. Robert O’Dell and Kerry P. Handron of Rice University observed 313 of the well‐resolved structures, which they call cometary knots; their glowing heads and wispy tails resemble comets. O’Dell and Handron estimate that the entire nebula has 3500 of them.
Gloria B. Lubkin; Helix Nebula Displays Hundreds of Gaseous Knots. Physics Today 1 June 1996; 49 (6): 19. https://doi.org/10.1063/1.2807648
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