page_title: Protoplanetary nebula
section_title: Protoplanetary nebula phase
hierarchical_section_title: Protoplanetary nebula / Evolution / Protoplanetary nebula phase
caption_attribution_description: English: The NASA/ESA Hubble Space Telescope has used its Advanced Camera for Surveys to peer closely at the strange cloud of gas and dust that envelops a star at a late stage in its life, a short-lived phenomenon known as a protoplanetary, or pre-planetary nebula. These fascinating celestial objects give astronomers an opportunity to watch the early stages of planetary nebula formation, as the gas and dust is moulded by high velocity winds — like watching a glassblower at work in his factory. Despite their rather confusing names, these objects are unrelated to planets. The name arose because of the superficial visual similarity between planetary nebulae and the small discs of the outer planets in the Solar System when viewed through a telescope. The protoplanetary nebula shown in this image is known as IRAS 20068+4051 and it is found in the constellation of Cygnus. The shell formed when its progenitor star exhausted its hydrogen fuel for nuclear fusion, causing the outer layers of the star to expand and cool, which created a spherical envelope of gas and dust around the star. The mechanism that drives high velocity winds to then shape this spherical envelope into the intricate structure that we see here is still unclear, which is why continued observation of protoplanetary nebulae is so important. Meanwhile, as the central star continues to evolve, finding new ways to prevent itself from collapsing under its own gravity, it will eventually become hot enough to make the gas glow as a spectacular planetary nebula. These objects emit a broad spectrum of radiation, including visible light, making them great targets for both amateur and professional astronomers. However, protoplanetary nebulae, which often appear smaller and are seen best in infrared light, are much trickier to observe, particularly since water vapour in the Earth’s atmosphere absorbs most infrared wavelengths. But Hubble has exceptionally sharp vision and an unobstructed vantage point in space, making it possible to capture stunning images of these peculiar objects. This picture was created from images taken through yellow (F606W, coloured blue) and near-infrared (F814W, coloured red) filters using the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The exposure times were 1280 s (F606W) and 200 s (F814W) and the field of view spans about 25 arcseconds.
context_page_description: A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch phase and the subsequent planetary nebula phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars.
context_section_description: During the ensuing protoplanetary nebula phase, the central star's effective temperature will continue rising as a result of the envelope's mass loss as a consequence of the hydrogen shell's burning.  During this phase, the central star is still too cool to ionize the slow-moving circumstellar shell ejected during the preceding AGB phase.  However, the star does appear to drive high-velocity, collimated winds which shape and shock this shell, and almost certainly entrain slow-moving AGB ejecta to produce a fast molecular wind.  Observations and high-resolution imaging studies from 1998 to 2001, demonstrate that the rapidly evolving PPN phase ultimately shapes the morphology of the subsequent PN.  At a point during or soon after the AGB envelope detachment, the envelope shape changes from roughly spherically symmetric to axially symmetric.  The resultant morphologies are bipolar, knotty jets and Herbig–Haro-like "bow shocks".  These shapes appear even in relatively "young" PPN. (Davis et al. 2005)
caption: Protoplanetary nebula known as Emperor Seiwa taken by Hubble's Advanced Camera for Surveys.
exif: {}