Ten thousand years ago, as glaciers from Earth’s last ice age retreated towards the poles and humans planted their first crops, a Sun-like star died. Fifteen years ago the Hubble Space Telescope observed its shattered remains. Thanks to Nasa’s open data policies I used that data to create my own portrait of the Eskimo Nebula.
Amateurs have been involved in the Hubble project from the beginning. Fourteen amateur astronomers got to use the space telescope in its early years in orbit. Budget cuts ended that program, but not amateur involvement with Hubble. Amateur astronomers regularly help professional scientists' Hubble-based research by supplementing space-based observations with dozens or hundreds of ground-based observations. Crowdsourced citizen science projects like GalaxyZoo rely on data from the Hubble’s archives to produce new science.
The Hubble teams even help amateurs make their own images from Hubble data. Both the American hubblesite and the European spacetelescope site host tutorials that explain image processing techniques. The public can share their versions of Hubble images with the Hubble Image Processors Facebook Group.
For this project I picked one of Hubble’s first targets following the 1999 servicing mission. Formally called NGC2392, but dubbed the Eskimo Nebula because of its appearance through amateur telescopes, it is a planetary nebula - the shattered remnants of a Sun-like star.
A star up to eight times the mass of the Sun won’t die in a supernova explosion. It sputters out instead. As the star’s fusion engine burns through its hydrogen and helium fuel, it expands to form a reg giant. Towards the end a series of convulsions blasts concentric shells of gas from the surface. Finally the core collapses to form a white dwarf. Its intense stellar wind streams at supersonic speeds in all directions while jets of particles shoot from the white dwarf’s poles. Shockwaves from the particles’ impacts twist the clouds into tortured shapes while intense ultraviolet light ionizes the gas to form the glowing nebula.
That’s what happened to NGC2392 ten thousand years ago. Thousands of years from now the gas clouds will disperse, leaving the white dwarf to slowly cool and fade like a campfire’s dying ember. In the meantime the planetary nebula glows in our skies for our appreciation and scientists’ exploration.
We are looking at the system from above its pole, giving the nebula its symmetrical appearance. The inner shell surrounding the white dwarf looks like overlapping rings from our perspective, but is actually an expanding peanut-shaped cloud. Beyond that extends a spherical outer shell cast off by the original star’s early spasms expands. Dense concentrations of gas ringing the star’s equatorial plane have formed light-year long filaments in the outer shell.
To create my version of the Eskimo Nebula, I dowloaded the original files from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute. This is the Nasa-funded public archive that holds data from many of the space agency’s orbiting telescopes. The scientists who schedule the observations collected three images using three different filters that correspond to the wavelengths where ionized oxygen, hydrogen, and nitrogen glow.
I colorized those images blue, green, and red respectively in Photoshop to create a false-color image. Tweaking the original images as well as the combined image let me bring out more detail within the inner shell and the radial filaments of the outer shell than in Nasa’s original press release image.
I didn’t take as radical a departure from the original as I did when creating my version of the Saturn Nebula. Despite the aesthetic differences, the two planetary nebulae are more similar than you’d think. Where we get a top-down, symmetrical view of the Eskimo Nebula, we are looking at the Saturn Nebula’s full length. Both share the peanut-shaped inner core with a more distant outer core. If we could travel through space, we would see that they were shaped by similar processes.