^{Image: Public Domain Clip Art: Helix Nebula}

"Now, a team of astronomers using observations from several observatories, including NASA's Hubble Space Telescope, has established that the Helix's structure is even more perplexing. Their evidence suggests that the Helix consists of two gaseous disks nearly perpendicular to each other." [14]



This three-dimensional model of the Helix Nebula illustrates, at left, the object as viewed in the plane of the sky, while the right image shows a cross section through the symmetry axis. "The relative width of the neutral hydrogen zone is unknown. Although drawn as open forms, the upper and lower structures above and below the main disk may be closed bubbles, either model being consistent with the observed outer arcs."

"Ordinary images of the helix give an immediate impression that there is an empty central core, a feature of all of the three-dimensional models of the nebula [see above]. However, the H image shown in Figure 1 [see below] argues that this is not the case, and the He II image establishes that this region has substantial material."   [15]

Appearance of the helix in various bands I) Left is the calibrated H image, and the right is the corresponding [O III] 5007 Å image.

Appearance of the helix in various bands II) The image on left is the 4697 filter image, which isolates the He II line at 4686 Å with the right image being 5007 Å divided by H emission. All of these images have had their stars edited out to show the emission only, and their field of view is 1180" × 1180".

Appearance of the helix in various bands III) These two images show the combined H (left) and 5007 Å images prior to editing out the stars and printed to show the fainter outer regions. The difference in the structure is discussed in the text. The field of these two images is 2360" × 2360". [Ibid, fig.1]

Color-coded image of the Helix Nebula illustrates the ionization stratification of this nebula. Red is used for emission in H, green for [O III], and blue for He II. The stars in the field have been edited out by interpolation from the adjacent pixels. The orientation is north up and west right. The field of view is 1180 × 1180. The zones defined in the text are well illustrated, with the He+2 zone appearing as blue, the He+ as yellow, and the He0 zone as red. The Astronomical Journal, 116:1346-1356, 1998 September

In a draft for the Astronomical Journal by O'Dell, Henney, and Ferland (received 8 Apr 2005 and issued February 2, 2008) the cometary-like knots of the Helix Nebula were studied for 1) their possible origins and, 2) their possible fate. Of the two goals it is the eventual fate of the knots which was deemed the more relevant. As pointed out by the study's authors:

"This is because their survival beyond the PN stage would mean that a large fraction of the material being put into the interstellar medium (ISM) by the PN phenomenon would be trapped in optically thick knots, which would then become a new component of the ISM. However, to delve into their origin or prognosticate their future, we must understand the objects as they are now. Fortunately, these knots have become the subjects of recent observational studies that probe from the outside to the inside of the knots and we can begin to hope of having a complete picture of their nature."   [16]

In short, the reasearch study was able to "...constructed a combined hydrodynamic+radiation model for the ionized portion of these knots and have accurately calculated a static model for their molecular regions."   [Ibid, pg. 1]


The upper three panels show 5.9''x 16.2'' samples around 378-801 from the WFPC2 programs GTO-5086 and GO-5311 selected to lie along the symmetry axis of the tail, which coincides with a radial line drawn towards the central star. The pixel scale has been adjusted to 0.05'' in order to agree with that of the STIS images. The diagonal feature across the [N II] cusp is an artifact in the original image. The upper left feature in the H(a) and [N II] images is probably a partially shadowed second knot that is unrelated to 378-801. The bands between the upper panels show the range of rows that were averaged when making the tail profiles shown in the lower three panels. The limb brightening seen in H(a) contrasts with the concentrated emission seen in [N II] and the concentrated extinction seen in [O III].

One day our Sun may look like this. The Helix Nebula is the closest example of a planetary nebula created at the end of the life of a Sun-like star. The outer gasses of the star expelled into space appear from our vantage point as if we are looking down a helix. The remnant central stellar core, destined to become a white dwarf star, glows in light so energetic it causes the previously expelled gas to fluoresce. The Helix Nebula, given a technical designation of NGC 7293, lies 450 light-years away towards the constellation of Aquarius and spans 1.5 light-years. The above image was taken with the Canada-France-Hawaii Telescope (CFHT) located atop a dormant volcano in Hawaii, USA. A close-up of the inner edge of the Helix Nebula shows unusual gas knots of unknown origin. Credit & Copyright: J.-C. Cuillandre (CFHT Staff), CFH12K CCD Camera, CFHT   [18]


Shown above and recorded in the ultraviolet by the Galaxy Evolution Explorer, is what I consider to be the second most beautiful image ever created of NGC 7293.   [19]


Yet, who can ever forget the deep rich image produced by the team of NASA, WIYN, NOAO, ESA, Hubble Helix Nebula Team, Margaret Meixner of the Space Telescope Science Institute and Travis Rector of the National Radio Astronomy Observatory -- an astronomical beauty for certain!   [20]