Planetary nebulae around dying stars

When Sun-like stars get old, they become cooler and redder, increasing their sizes and energy output tremendously: they are called red giants. Most of the carbon (the basis of life) and particulate matter (crucial building blocks of solar systems like ours) in the universe is manufactured and dispersed by red giant stars. When the red giant star has ejected all of its outer layers, the ultraviolet radiation from the exposed hot stellar core makes the surrounding cloud of matter created during the red giant phase glow: the object becomes a planetary nebula. The star cools off to become a white dwarf.

A long-standing puzzle is how planetary nebulae acquire their complex shapes and symmetries, since red giants and the gas/dust clouds surrounding them are mostly round. Hubble's ability to see very fine structural details (usually blurred beyond recognition in ground-based images) enables us to look for clues to this puzzle.

• CRL2688: The "Egg Nebula".
• The Egg Nebula in infrared light.
• NGC 6543a: The "Cat's Eye Nebula".
• MyCn 18: The "Hourglass Nebula".
• NGC 7027.

CRL2688 This image of the Egg Nebula, also known as CRL2688 and located roughly 3,000 light-years from us. The nebula is really a large cloud of dust and gas ejected by the star, expanding at a speed of 20 km/s (115,000 mph). A dense cocoon of dust (the dark band in the image center) enshrouds the star and hides it from our view. Starlight escapes more easily in directions where the cocoon is thinner.

HUBBLE FINDS SEARCHLIGHT BEAMS AND MULTIPLE ARCS AROUND A DYING STAR
(R. Sahai and J. Trauger. 16-1-1996)

The Egg Nebula, also known as CRL 2688, is shown on the left as it appears in visible light with the Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) and on the right as it appears in infrared light with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Blue corresponds to starlight reflected by dust particles, and red corresponds to heat radiation emitted by hot molecular hydrogen. The distance between the tip of each jet is approximately 200 times the diameter of our solar system (out to Pluto's orbit).

Press Release:

• NICMOS PEERS INTO HEART OF DYING STAR
  Rodger Thompson, Marcia Rieke, Glenn Schneider, Dean Hines (University of Arizona); Raghvendra Sahai (Jet Propulsion Laboratory); NICMOS Instrument Definition Team, and NASA
  April 12, 1997

NGC 6543a Nicknamed the "Cat's Eye Nebula", is located about 3,000 light-years away, in the direction of the constellation Draco. We can see it now as it was 1000 years after the outburst started.

HUBBLE PROBES THE COMPLEX HISTORY OF A DYING STAR
(J.P. Harrington and K.J. Borkowski. 11-1-1995)

MyCn18 MyCn18 is a a young planetary nebula located about 8,000 light-years away. In previous ground-based images, it appeared to be a pair of large outer rings with a smaller central one. It looked like supernova 1987A. This Hubble image reveals the true shape of MyCn18 to be an hourglass with a complex pattern of "etchings" in its walls. The hot star which has been thought to eject and illuminate the nebula, and therefore expected to lie at its center of symmetry, is clearly off center. This fact has been observed recently in the nucleus of some active galaxies, around what could be a black hole.

HUBBLE FINDS AN HOURGLASS NEBULA AROUND A DYING STAR
(R. Sahai and J. Trauger. 16-1-1996)

NGC 7027 This planetary nebula is located about 3,000 light-years from Earth in the direction of the summer constellation Cygnus. The Hubble photo reveals that the initial ejections occurred episodically to produce the concentric shells. This culminated in a vigorous ejection of all of the remaining outer layers, which produced the bright inner regions.

HUBBLE TELESCOPE PHOTO REVEALS STELLAR DEATH PROCESS
(H. Bond. 16-1-1996)