This serene cloud of gas belies a lot of activity deep within the nebula.
NGC 6891 glows brightly in a new image from the Hubble Space Telescope, as the observatory assists scientists in learning more about how these gas clouds formed and evolved.
Astronomers call NGC 6891 a “planetary nebula,” a term arising from an old misidentification with planets back when telescope technology was in its infancy. Today we know that such nebulas form after supernova explosions that see huge stars shed gas. A white dwarf remnant of the star remains behind, slowly cooling.
The Hubble Space Telescope’s high-definition imagery revealed knots and filaments wrapped around the white dwarf embedded deep within the cloud. The data also shows that the outer halo of gas is expanding faster than the innermost part of the nebula, and the observations even catch shells of gas that are oriented in different directions.
“From their motions, astronomers estimate that one of the shells is 4,800 years old while the outer halo is some 28,000 years old, indicating a series of outbursts from the dying star at different times,” NASA officials wrote in a statement.
The glowing from NGC 6891 occurs as the white dwarf stars ionizes, or strips away electrons, from the surrounding hydrogen gas.
“As 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,” NASA said.
Hubble is currently in recovery from a synchronization glitch that occured on Oct. 23 and its instruments are slowly being brought back online. Hubble was last serviced in person in 2009 and with the retirement of the space shuttle, is no longer accessible to astronauts. That said, the 31-year-old telescope has plenty of archival data to process.