Death Throes

Credit: NASA/JPL-Caltech/ J. Hora (Harvard-Smithsonian CfA)

Comet col­li­sions may be kick­ing up dust in the Helix Neb­ula in this image from NASA’s Spitzer Space Tele­scope.

Resem­bling a giant, shim­mer­ing eye, the Helix Neb­ula was a star much like our Sun. When a star like our Sun burn all of the hydro­gen that fuels nuclear fusion in their cores, the star begins to shed its outer lay­ers, puff­ing them out into space as giant bub­bles. Astronomers call these cos­mic beau­ties plan­e­tary neb­ula. Radi­a­tion from the dead star’s white hot core, called a white dwarf, heats the expand­ing shell of mate­r­ial caus­ing it to glow. The glow is short-lived, how­ever, last­ing for only about 10,000 years.

Plan­e­tary neb­u­lae have noth­ing to do with plan­ets. Early planet seek­ers noticed many objects in the sky that resem­bled the glow­ing orbs of known gas plan­ets, such as Jupiter, Sat­urn and Uranus. It wasn’t until much later that sci­en­tists dis­cov­ered the dead stars’ true origin.

Images in vis­i­ble light of the Helix Neb­ula show a spec­tac­u­larly col­or­ful bub­ble around the cen­tral star but no real detail. With Spitzer’s infrared tele­scope, how­ever, dust not pre­vi­ously seen was found cir­cling the star at a dis­tance of 35 to 150 astro­nom­i­cal units. An astro­nom­i­cal unit is the dis­tance between Earth and the Sun; about 93 mil­lion miles. The glow of the dust encir­cling the dead star sur­prised astronomers. They believe the dust is most likely churned up by comets smash­ing into each other at the fringes of this doomed solar system.

The Helix Neb­ula is found only about 700 light-years from Earth toward the zodi­a­cal con­stel­la­tion Aquar­ius, the Water Bearer.