Eye of Sauron
Published on Jan 9, 2008 at 10:39 pm.
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Filed under conference blogging, nebula.
This is an infrared image of NGC 7293, also known as the Helix Nebula. It is an example of a planetary nebula. The term “planetary” does not mean that the nebula has anything at all to do with planets. Rather, it is a holdover from the terminology used by William Hershel, who observed that these nebulae tend to appear to be round, like planets.
When a star like the Sun dies, it swells up and starts to pulsate. Eventually, its outer layers are pushed off into space to form an expanding cloud of gas around the star. The core collapsed to form a stellar remnant called a white dwarf. The cloud of expanding gas is the planetary nebula. Formation of a planetary nebula is usually one of the last things that happens in the life of a solar-type star.
The Helix Nebula is already well known for its famous image seen here
taken by the Hubble Space Telescope. But, the image above is a new one taken by the Spitzer Space Telescope. At one of the talks that I heard today, someone from the Spitzer team was talking about something else, but he mentioned the remarkable resemblance of this image to the flaming eye of the Dark Lord Sauron, as portrayed in the film version of J. R. R. Tolkien’s Lord of the Rings.
But, there is something else interesting in the new infrared image from Spitzer. If you look carefully you see the red dot at the middle of the image that is the white dwarf. But, you also see what looks like a disk around it. Astronomers believe that the disk is formed from dust shed by colliding comets around the white dwarf. As the outer layers were shed to form the planetary nebula, the comets and dwarf planets orbiting the planet had their orbits disrupted. The comets began to fall back closer to the white dwarf and began colliding. As they collide, they shed material, but they also would build larger bodies. In effect, they may be forming planetessimals which can then collide to form planets. This is believed to be how the planets Neptune and Uranus formed in our own solar system. So, we may be watching the byproducts of the formation of watery planets around the white dwarf at the center of NGC 7293. Now, how cool is that?
-Astroprof
Images courtesy of NASA, Spitzer, HST
