Planetary Nebulae

It Starts with a Star

A normal star gets its heat from the nuclear fusion of hydrogen, which creates helium as the end product. As the star uses up hydrogen, the more massive helium sinks to the core. The helium cannot fuse in turn because it takes far more energy to get that process going. However, the core of the star becomes more and more compressed as the helium builds up, and eventually, the gravity of the core can create enough energy to get the helium to fuse. Helium fusion creates far more energy than hydrogen fusion—so much energy that it usually destroys the star!

The Star is Destroyed

The extra energy in the core pushes the rest of the star into space leaving the core behind. The core loses most of the pressure that made it fuse, so that process stops, and the core slowly cools off. We call the remaining core a white dwarf, and the expanding ring of debris from the rest of the star is called a planetary nebula. (A planetary nebula has nothing to do with planets except that it is often round.)

A Complex Explosion

Astronomers expected that every planetary nebula would be round, but actually, most are not. Many of them have a series of shells on the outside. These shells are created when the extra fusion in the core stutters—getting started then dying out a few times. Each time, some of the star is pushed away, but then the star pulls itself back together and goes back to normal for a while. The material lost creates one shell. Many planetary nebulae also have an hourglass shape. This is caused by the magnetic field of the star funneling material primarily in two directions. Other planetary nebulae have even more complex and bizarre shapes which we don't yet understand.




parent directory
Back Up to
Deep Space
Cat's Eye
Cat's Eye
Regular Size
Full Size
Caption
Credit: NASA/ESA/HEIC/Hubble Heritage Team (STScI/AURA)
Butterfly Nebula
Butterfly Nebula
Regular Size
Large Size
Full Size
Caption
Credit: NASA/ESA/Hubble SM4 ERO Team
NGC 2818
NGC 2818
Regular Size
Full Size
Caption
Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA)
Gallery
Gallery
Regular Size
Full Size
Caption
Credit: Hubble Heritage; Jim Misti; NASA/ESA/A. Fruchter/H. Van Winckel/M. Cohen/H. Bond/T. Gull
Hubble Heritage; NASA/R. Sahai/J. Trauger/WFPC2 Team; NASA/ESA/Hubble Heritage; Hubble Heritage

Retina
Retina
Regular Size
Full Size
Caption
Credit: NASA/Hubble Heritage Team (STScI/AURA)


Little Ghost
Little Ghost
Regular Size
Full Size
Caption
Credit: NASA/Hubble Heritage Team (STScI/AURA)


Spacemandan.net