PDA

View Full Version : Bad Astronomy in Sky & Telescope: Supernovae



Crimson
2007-Jun-05, 11:36 PM
The sidebar "The Creative Side of Supernovae" on page 29 of the March 2007 issue of Sky and Telescope contains erroneous claims about nucleosynthesis.


supernovae synthesized and dispersed many of the heavy elements (such as oxygen, calcium, phosphorus, and silicon) that built the planets and made life possible on Earth.

No, supernovae did not synthesize most of these elements. For example, oxygen arose when the pre-supernova star burned helium. Then the supernova explosion dispersed the oxygen into space. But the explosion did not create most of the oxygen.


Supernovae also created the elements heavier than iron (such as nickel, lead, and uranium) that human society exploits for machines and energy.

Supernovae did create most of the elements heavier than iron, but not all of them--and not most lead.

There are two main ways that elements heavier than iron arose. The first is the r-process, in which a rapid flux of neutrons transforms iron-peak nuclei into heavier ones. The r-process is thought to occur in supernova explosions and created most gold, platinum, silver, and most other elements heavier than iron, including all uranium.

But there is another process, the s-process, that also created some of the elements heavier than iron. The s-process occurs when a slow flux of neutrons transforms iron-peak nuclei into heavier ones. It operates in red giants and supergiants, not supernovae. According to Table 5 of Burris et al. (http://adsabs.harvard.edu/abs/2000ApJ...544..302B) in The Astrophysical Journal, volume 544, page 302, the following elements--all heavier than iron--are made mostly by the s-process: gallium, krypton, strontium, yttrium, zirconium, niobium, molybdenum, tin, barium, lanthanum, cerium, tungsten, mercury, thallium, and lead. Recent research suggests that we can add copper to this list.

Meanwhile, the July 2007 issue of Sky and Telescope contains an error the magazine has made before. Page 33 has a picture of a supernova and the caption: "In March 1994 a Type Ia supernova erupted on the outskirts of NGC 4526, an edge-on disk galaxy in Virgo."

But that supernova probably did not occur in the galaxy's outskirts. The June 2004 issue of the magazine ran the same picture with a similar caption, prompting a letter from Vera Rubin that appeared on page 12 of the September 2004 issue: "[C]ontrary to the caption, the supernova is probably not in the outskirts of the galaxy. The beautiful gas and dust disk, which looks so dim and mysterious in the photo, is a small, rapidly rotating nuclear disk with a radius only about 7 percent of the optical radius of the galaxy. If the supernova is located in or near the principal plane of NGC 4526, then its distance from the center is less than 15 percent of the galaxy's visible radius."