Hubble Space Telescope picture of NGC 6891. Credit: NASA, ESA, A. Hajian (University of Waterloo), H. Bond (Pennsylvania State University), and B. Balick (University of Washington); Processing: Gladys Kober (NASA/Catholic University of America).
NGC 6891 is a brilliant, asymmetrical planetary nebula in the constellation Delphinus, the Dolphin. This Hubble image exposes a wealth of structure, consisting of a round external halo that is broadening much faster than the inner nebula, and a minimum of 2 ellipsoidal shells that are orientated differently. The image likewise exposes filaments and knots in the nebulas interior, surrounding the main white dwarf star. From their motions, astronomers approximate that a person of the shells is 4,800 years of ages while the external halo is some 28,000 years of ages, suggesting a series of outbursts from the dying star at various times.
Hubble studied NGC 6891 as part of efforts to gauge the distances to nebulae, and to learn more about how their structures formed and evolved. NGC 6891 is made up of gas thats been ionized by the main white dwarf star, which stripped electrons from the nebulas hydrogen atoms. As the stimulated electrons revert from their higher-energy state to a lower-energy state by recombining with the hydrogen nuclei, they give off energy in the kind of light, triggering the nebulas gas to radiance.
By NASAs Goddard Space Flight Center
December 4, 2021
