NGC 6891 is a shiny, asymmetrical planetary nebula within the constellation Delphinus, the Dolphin. This Hubble picture reveals a wealth of construction, together with a spherical outer halo that’s increasing quicker than the interior nebula, and a minimum of two ellipsoidal shells which are oriented otherwise. The picture additionally reveals filaments and knots within the nebula’s inside, surrounding the central white dwarf star. From their motions, astronomers estimate that one of the shells is 4,800 years previous whereas the outer halo is a few 28,000 years previous, indicating a sequence of outbursts from the dying star at totally different instances.
Hubble studied NGC 6891 as half of efforts to gauge the distances to nebulae, and to be taught extra about how their buildings fashioned and developed. NGC 6891 is made up of fuel that’s been ionized by the central white dwarf star, which stripped electrons from the nebula’s hydrogen atoms. Because the energized electrons revert from their higher-energy state to a lower-energy state by recombining with the hydrogen nuclei, they emit vitality within the type of gentle, inflicting the nebula’s fuel to glow.