If we could see in three dimensions instead of two, we’d never have thought otherwise.
Perhaps the most famous sight of a dying star is the Ring Nebula, discovered in 1779.
The Ring Nebula appears to be an enormous gaseous ring surrounding a white dwarf star. This is representative of the fate of Sun-like stars that aren’t part of multi-star systems. Despite its appearances, this isn’t a true ring after all. (NASA, ESA, AND C. ROBERT O’DELL (VANDERBILT UNIVERSITY))
At just over 2,000 light-years distant, it’s the closest dying star to Earth.
In between the 2nd and 3rd brightest stars of the constellation Lyra, the blue giant stars Sheliak and Sulafat (shown prominently here), the Ring Nebula can easily be identified with any telescope or even a pair of binoculars. (NASA, ESA, DIGITIZED SKY SURVEY 2)
Upon observing it, Charles Messier wrote: “it is very dull, but perfectly outlined; it is as large as Jupiter & resembles a planet which is fading.”
This observation originated the misnomer “planetary nebula,” but physically originates when dying stars expel their outer layers.
The elements of the periodic table, and where they originate, are detailed in this image above. While most elements originate primarily in supernovae or merging neutron stars, many vitally important elements are created, in part or even mostly, in these planetary nebulae like the Ring Nebula. (NASA/CXC/SAO/K. DIVONA)
Despite looking very much like a ring to our eyes, the Ring Nebula is anything but.
Planetary nebulae take a wide variety of shapes and orientations depending on the properties of the stellar system they arise from, and are responsible for many of the heavy elements in the Universe. Supergiant stars and giant stars entering the planetary nebula phase are both shown to build up many important elements of the periodic table via the s-process. (NASA, ESA, AND THE HUBBLE HERITAGE TEAM (STSCI/AURA))
A huge, diffuse set of hydrogen shells surround it, showcasing recently blown-off material as the star dies.
The red outer shells are signs of ionized hydrogen gas, huge and intricate outside the ring itself. Sulfur and Oxygen ions, expelled from the star and prominent in the ring area, are viewed in the other colors shown here. Spectroscopic imaging, where particular emission lines from a specific element, is key to teasing out these features. (D. LÓPEZ (IAC), WHICH IS A. OSCOZ, D. LÓPEZ, P. RODRÍGUEZ-GIL AND L. CHINARRO)
Along our line-of-sight, lobes of low-density gas extend both towards and away from us.
The Helix Nebula, a similar planetary nebula (with a donut-shaped appearance) to the Ring Nebula, has also had its 3D structure mapped out. It, too, is far more intricate than a simple ring explanation would indicate. (NASA, ESA, C.R. O’DELL (VANDERBILT UNIVERSITY), AND M. MEIXNER, P. MCCULLOUGH, AND G. BACON ( SPACE TELESCOPE SCIENCE INSTITUTE))
Our perspective view this structure almost directly down one of its poles, explaining its ring-like appearance.
The Spitzer Space Telescope, looking in infrared light, showcases the temperature of different portions of the Ring Nebula. The inner regions are far hotter, which explains why they’re far brighter. The electrons that were excited or ionized that then fall down in their orbitals is what causes the emission of the light that we can see, and that preferentially happens in the hottest regions. (NASA/JPL-CALTECH/J. HORA (HARVARD-SMITHSONIAN CFA))
In 2013, astronomers used new Hubble data to map out the nebula’s 3D structure.
This schematic shows the geometry and structure of the Ring Nebula (Messier 57) as it would appear if viewed from the side, rather than along our line-of-sight. This shows the nebula’s wide halo, inner region, lower-density lobes of material stretching towards and away from us, and the prominent, glowing disc. (NASA, ESA, AND A. FEILD (STSCI))
The reflective, high-density gas is all most telescopes ever observe.
Through a modest-sized telescope at a dark-sky site, this is what the Ring Nebula will appear to look like through an eyepiece to a human observer. The origin of the name ‘Ring Nebula’ is apparent, but the true story is far more revealing. (CHRIS SPRATT)
But we now know it isn’t a ring at all, but also displays intricate structure, with an outer halo, inner turbulence, lobes and knots.
The different elements (in different colors), the neutral knots of gas (dark globs), and the translucent hue of the inner ring are all artifacts of viewing this intricate 3D structure face-on. The Ring Nebula is no ring at all, nor is it spherical in shape. Its true nature is far more complex, and has taken a variety of observations to reveal. (NASA, ESA, AND C. ROBERT O’DELL (VANDERBILT UNIVERSITY))
This may be the exact fate awaiting the Sun in our distant future.
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