In one of the largest and most detailed celestial images ever made, the coil-shaped Helix Nebula is being unveiled today in celebration of Astronomy Day. The resulting composite picture is a seamless blend of ultra-sharp NASA Hubble Space Telescope images combined with the wide view of the Mosaic Camera on the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, Arizona. The image shows a fine web of filamentary “bicycle-spoke” features embedded in the colorful red and blue gas ring, which is one of the nearest planetary nebulae to Earth.
Because the nebula is nearby, it is nearly one-half the diameter of the full Moon. This required that Hubble astronomers take several exposures with the Advanced Camera for Surveys to capture most of the Helix. The Hubble views were then blended with a wider photo taken by Kitt Peak’s Mosaic Camera.
The portrait offers a dizzying look down what is actually a trillion-mile-long tunnel of glowing gases. The fluorescing tube is pointed nearly directly at Earth, so it looks more like a bubble than a cylinder. A forest of thousands of comet-like filaments embedded along the inner rim of the nebula points back toward the central star, which is a small but super-hot white dwarf. These tentacles formed when a hot stellar “wind” of gas plowed into colder shells of dust and gas ejected previously by the doomed star. These comet-like filaments have been known from ground-based telescopes for decades, but never before seen in so much detail. They may actually lie in a disk encircling the hot star like a collar.
Valuable Hubble observing time became available during the November 2002 Leonid meteor storm. To protect the spacecraft, including Hubble’s precise mirror, controllers turned Hubble’s aft end into the direction of the meteor stream for about half a day. Fortunately, the Helix Nebula was almost exactly in the opposite direction of the meteor stream, so Hubble used nine orbits to photograph the nebula while it waited out the storm. To capture the sprawling nebula, Hubble had to take nine separate snapshots. Astronomers at the Space Telescope Science Institute assembled these images into a mosaic. The mosaic was then blended with a wider photograph taken by the Mosaic Camera on the National Science Foundation’s 0.9-meter telescope at Kitt Peak National Optical Astronomy Observatory. The radiant tie-die colors correspond to glowing hydrogen and nitrogen (red) and oxygen (blue).
Planetary nebulae like the Helix are sculpted late in a Sun-like star’s life by a torrential gush of gases escaping from the dying star. They have nothing to do with planet formation, but got their name because they look like planetary disks in a small telescope. With higher magnification, the classic “donut-hole” in the middle of a planetary nebula can be resolved. Based on the nebula’s distance of 650 light-years, its angular size corresponds to a huge ring diameter of nearly 3 light-years across. That’s approximately three-quarters of the distance between our Sun and the nearest star.
The Helix Nebula is a popular target of amateur astronomers and can be seen with binoculars as a ghostly, greenish cloud in the constellation Aquarius. Larger amateur telescopes can resolve the ring-shaped nebula, but only the largest ground-based telescopes can resolve the radial streaks. After careful analysis, astronomers conclude that the nebula really isn’t a bubble, but is a cylinder that happens to be pointed toward Earth.
Credit: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO).
Electronic image files and additional information are available at:
The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by AURA under a cooperative agreement with the National Science Foundation.