NASA/ESA Hubble Space Telescope recently shared the image of an asymmetrical planetary nebula called NGC 6891. Located in the Dolphin’s constellation Delphinus, the nebula is bright and has a somewhat complex structure.
The observation of this asymmetrical planetary nebula was a part of the effort to calculate the distances to nebulae and learn more about their evolution.
NGC 6891 has a spherical outer halo that is expanding faster than the inner nebula. It has at least two ellipsoidal shells that are orientated differently.
The new Hubble’s image also revealed the nebula’s interior: filaments and knots surrounding the central white dwarf star. Their motions help astronomers estimate the ago of its shells.
One of the shells is 4,800 years old, while the outer halo is some 28,000 years old. Their age indicates a series of outbursts from the dying star at different times.
The central white dwarf ionized the gas that made this asymmetrical planetary nebula.
NASA noted in their blog, “The energized electrons revert from their higher-energy state to a lower-energy state by recombining with the hydrogen nuclei, they emit energy in the form of light, causing the nebula’s gas to glow.”