Tunnel Vision – Step Into the “Ring”…

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Who doesn’t recognize this awesome image of Messier Object 57 which was taken by the Hubble Space Telescope? The original color image was assembled from three black-and-white photos taken through different color filters with the Hubble’s Wide Field Planetary Camera 2. We know the blue filtration isolates emission from very hot helium, which is located primarily close to the hot central star… just as green represents the further away ionized oxygen and cool red shows ionized nitrogen gas at the farthest position of all. We know where they’re supposed to be, but we’ve never quite seen it in dimension until it’s been visualized by the “magic” of Jukka Metsavainio…

Like all our our “stereo” image produced for UT by Jukka Metsavainio, two versions are presented here. The one above is parallel vision – where you relax your eyes and when you are a certain distance from the monitor screen the two images will merge into one to produce a 3D version. I have heard from a friend recently that if you place a card in the center of the image with the edge towards you, it aids in seeing the parallel version. (And he was right.) The second – which appears below – is crossed vision. This is for those who have better success crossing their eyes to form a third, central image where the dimensional effect occurs. (The card “trick” also works well here, too!) Jukka’s visualizations of what Hubble images would look like if we were able to see them in dimension come from studying the object, its known field star distances and the different wavelengths of light. Are you ready to “cross” the boundary and step into the “Ring” for another round with Messier 57? Then let’s rock…

Originally discovered by discovered by Antoine Darquier de Pellepoix in January, 1779 and independently found by Charles Messier later that same month, it was Darquier who first said that it was “…as large as Jupiter and resembles a planet which is fading.” Thanks to his description, the term ” planetary nebula” stuck because of their similarity in appearance to giant planets when viewed through small optical telescopes. However, Sir William Herschel wasn’t quite so aperture limited, and he was the first to propose this new object was a nebula was formed by multiple faint stars. By 1800, Count Friedrich von Hahn had discovered M57’s central star and within 64 years William Huggins was studying its spectral signature. Just a blink of a cosmic eye later, another 22 years, Hungarian astronomer Jen? Gothard had discovered it had a planetary nebula nucleus.

What has remained constant over the years is the classic bipolar structure associated with the “Ring” nebula – a prolate spheroid with strong concentrations of material along its equator. Its symmetrical structure is one of the best known in the night sky – right down to the knots along the edges that can often be observed with larger telescopes. What exactly are they? According to C.R. O’Dell (et al); ” The equator of the Ring Nebula is optically thick and much denser than the optically thin poles. The inner halo surrounding NGC 6720 represents the pole-on projection of the AGB wind at high latitudes (circumpolar) directly ionized by the central star, whereas the outer, fainter, and circular halo is the projection of the recombining AGB wind at mean to low latitudes, shadowed by the main nebula. The spatio-kinematical properties of the Ring Nebula and the origin of the dense knots commonly observed in late-stage planetary nebulae are critically compared with the predictions of radiation-hydrodynamic and wind interaction models.”

These winds, bubbles and explosions were part of the original Hubble photograph where our visualization came from. “We have studied the closest bright planetary nebulae with the Hubble Space Telescope’s WFPC2 in order to characterize the dense knots already known to exist in NGC 7293.” says O’Dell, “We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406 on the one extreme and the highly symmetric “cometary” knots seen in NGC 7293. The intermediate form knots seen in NGC 2392, NGC 6720, and NGC 6853 would then represent intermediate phases of this evolution.”

Anyone who is willing to step into the ring with this champion of all planetary nebulae is liable to end up with a few knots somewhere! Enjoy your tunnel vision journey….