The Southern Ring Nebula (Eight-Burst Nebula, NGC 3132) is a planetary nebula about 2,000 light-years away in the southern constellation Vela. With an apparent magnitude of 9.87 and an apparent size of 62 by 43 arcseconds, it can be observed in amateur telescopes. In 2022, the nebula became one of the first targets of NASA’s James Webb Space Telescope (JWST).
NGC 3132 was nicknamed the Southern Ring Nebula because of its resemblance to the better-known Ring Nebula (Messier 57) in the northern constellation Lyra. The name Eight-Burst Nebula comes from the nebula’s appearance, which resembles the figure 8 in some telescopes.
The Southern Ring Nebula is catalogued as NGC 3132 in the New General Catalogue and as Caldwell 74 in the Caldwell catalogue of deep sky objects visible in amateur telescopes.
Planetary nebulae are the final stage in the lives of intermediate-mass stars that evolve away from the main sequence and expand into red giants. In the late red giant phase, the stars periodically expel layers of material and ultimately end up surrounded by huge shells of gas and dust. These shells are ionized by the exposed hot stellar cores, the remnants of the central stars. The same fate awaits our Sun in about 6 billion years.
The Southern Ring Nebula and other planetary nebulae are in effect the expelled outer layers of evolved stars that reached the end of their lives. They are called planetary nebulae because their round shape vaguely resembles that of a planet when seen through a telescope. The nebulae do not, however, have anything to do with planets. The origin of the term “planetary nebula” is uncertain, but it was used before the 19th century.
Planetary nebulae are relatively short-lived phenomena. They only last for about 10,000 years before the central stars cool so much that the surrounding nebulosity becomes invisible to us. The Southern Ring Nebula will dissipate in only thousands of years.
The elements contained within planetary nebulae, such as carbon, oxygen, and nitrogen, are recycled into the surrounding space. They may be used to form new stars and planets. New generations of stars formed in these environments tend to have higher metallicities. Even though they only contain relatively small amounts of metals, these elements hugely impact their evolution.
The Southern Ring Nebula has a diameter of 0.4 light-years. The expanding cloud of gas was created when an aging star blew off its outer layers, leaving behind a hot remnant core. The central star periodically shed shells of dust and gas in all directions over thousands of years. The ejected material – the glowing gas – now forms the planetary nebula. The ultraviolet light of the central star ionizes the expanding shell, producing the appearance of a brightly coloured nebula.
The white dwarf has a surface temperature of about 100,000 kelvin. The hot surface of the faint star is heating the gas in the nebula.
The central star has a close 10th magnitude companion. The companion has not yet reached the end of its lifetime, but will likely produce a planetary nebula of its own when it does. The planetary nebula nucleus (PNN) itself is a 16th magnitude star. Both stars are lighting up the nebula’s outer layers. The ejected gas is expanding away from the central white dwarf at a speed of 9 miles per second. The hottest gas lies in the inner region, while the coolest is the farthest from the central star, at the edge of the nebula.
James Webb Telescope image
The Southern Ring Nebula was one of the first targets of NASA’s James Webb telescope, the successor to Hubble. An image of NGC 3132 was released along with those of the galaxy group Stephan’s Quintet in the constellation Pegasus, the Carina Nebula in Carina, the deep field view of the galaxy cluster SMACS 0723 in Volans, and the exoplanet WASP-96b in Phoenix.
The Webb observations show a much more detailed view of the Southern Ring Nebula than the Hubble image. The nebula appears almost face-on. If it appeared edge-on, its 3D shape would resemble two bowls connected at the bottom, opening away at the sides with a large hole at the centre.
The JWST images were captured with the Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) and unveiled on Tuesday, July 12, 2022. The exposure dates were June 3 (NIRCam) and June 12, 2022 (MIRI). The NIRCam image has a higher resolution, while the MIRI image reveals the dust around the central stars.
The white dwarf appears larger and reddish in mid-infrared wavelengths because it is embedded in a dense layer of dust. The star has probably expelled its last layers by now and it is unclear why it is cloaked in dust. The material may have been transferred from the brighter companion. The companion, appearing blue in the MIRI image, is in a tight orbit. It has not yet reached the final stages of its life cycle.
The companion orbits the hot white dwarf as the latter periodically expels shells of material, and it helps distribute the ejected gas and dust. Together, the binary system produces the nebula’s wispy asymmetrical shells.
Each shell of gas is the product of a mass loss episode. The widest cooler shell was expelled earlier, while those closer to the center of the nebula were ejected more recently. The central star has expelled at least eight layers of dust and gas over the last several thousand years. The shells allow astronomers to study the history of the system. The distribution of molecules within the gas cloud will help further the understanding of these objects.
A blue filament appearing on the left side of the mid-infrared image is an edge-on galaxy. Zooming in on the galaxy in the near-infrared image will reveal its dark dust lane. It is the most conspicuous of the distant galaxies captured by the JWST. The galaxies that appear small and red are the farthest away. The full-resolution images of the nebula can be downloaded at WebbTelescope.org.
The near-infrared image of the Southern Ring Nebula reveals the holes in the gas that allow the light of the central stars to pass through. The fine rays of light are visible in the image. Some of the starlight cannot escape from areas in the central region where the dust and gas are denser. The central white dwarf appears along the diffraction spikes of the companion, at the 8 o’clock position.
The James Webb Space Telescope, the most powerful orbital space telescope built to date, is an international project led by NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). Launched on December 25, 2021, the vast telescope was designed primarily for infrared astronomy. Its resolution and sensitivity will allow astronomers to study the formation of the first galaxies, investigate stellar nurseries and potentially habitable exoplanets, and see the light of objects formed in the early universe. In addition to capturing spectacular cosmic objects, these observations will help scientists gain a better understanding of the universe and how it evolved after the Big Bang.
NGC 3132 was previously imaged by the Wide Field and Planetary Camera 2 (WFPC2) on NASA’s Hubble Space Telescope in the mid-1990s. The image of the nebula was taken in December 1995 and released in November 1998.
The image produced by the Hubble Heritage Team at the Space Telescope Science Institute (STScI) showed the two stars at the centre of the nebula: a bright one and a much fainter companion. The fainter star is the central white dwarf. It lights up the surrounding nebula with ultraviolet radiation that makes the nebular material fluorescent. The nebula’s unusual shape and the asymmetries of its structure captured in Hubble’s 1-hour exposure are still not well understood.
The nebula is largely unknown to observers in the northern hemisphere because it stays below the horizon for most of the year. It makes an appearance low above the southern horizon in the winter months. Lying at declination 40° 26’ S, it cannot be seen from locations north of the latitude 48 – 49° N.
Observers in the southern hemisphere can see the Southern Ring Nebula for most of the year. The nebula is one of the most popular targets among amateur astronomers. Telescopes will reveal the nebula’s oval shape, but the intricate filaments and details of the nebula’s structure can only be captured photographically.
The best time of year to see the stars and deep sky objects in Vela is during the month of March, when the constellation rises high above the horizon in the evening sky.
Southern Ring Nebula – NGC 3132
|Right ascension||10h 07m 01.7656422504s|
|Declination||−40° 26′ 11.130553032″|
|Apparent size||62” x 43”|
|Distance||2,000 light-years (613 parsecs)|
|Names and designations||Eight-Burst Nebula, Southern Ring Nebula, NGC 3132, Caldwell 74, ESO 316-27, Hen 2-40, PK 272+12 1, PKS J1007-4026, PKS 1004-401, PN G272.1+12.3, VV 54, VV’ 94, ARO 504, StWr 4-8, WRAY 15-501|