November 30, 2013
Abell 70, a planetary nebula in Aquila
Image Credit & Copyright: Adam Block/Mount Lemmon SkyCenter/University of Arizona (http://skycenter.arizona.edu/gallery/nebulae/Abell70)
Abell 70 (also known as PN G038.1-25.4) is a planetary nebula that lies between 13,500 and 17,500 light-years away from Earth in the northern constellation of Aquila (the Eagle). It is approaching us at about 79 kilometers per second, while it is expanding at approximately 38 kilometers per second.
Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose in the 18th century because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through small optical telescopes. The name has stuck even though modern telescopes make it obvious that these objects are not planets at all.
When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.
This ring-shaped planetary nebula with a patchy surface was only discovered in 1955 by George Abell. Its northern edge seems to be illuminated by a light streak with an even brighter knot in its center. This is an edge-on radio galaxy shining through the nebula, called PMN J2033-0656. This galaxy, which is probably several million light-years away from us, appears to be about the same size as the relatively nearby planetary nebula, but, of course, is much larger. Abell 70 just happens to be in the line of sight between us and the distant galaxy.
The central star of Abell 70 is found to be a special type of binary system, with only two or three known analogues, consisting of a hot white dwarf and a barium star, a cool red giant with an overabundance of singly ionized barium (Ba II) as well as a high abundance of carbon and other heavy elements such as singly ionized strontium (Sr II).
Planetary nebulae last for only about 10,000 years, a very short period in the 10-billion-year lifespan of Sun-like stars. So, over the next several thousand years, Abell 70 will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.
This image is taken in May 2013 with a SBIG STX16803 CCD Camera on the 32-inch Schulman Telescope (RCOS) at the Mount Lemmon SkyCenter, using an Astrodon Gen II filter.