The Astrophysics Spectator

Issue 2.13, March 30, 2005

Home Commentary Surveys Research Background Store Previously Site Info
Logo for The Astrophysics Spectator.

The basic layout of the site is as survey paths, which can be found under the Surveys link at the top of this and most other pages on this site. Each survey begins with a basic overview of the subject. Part of this overview include simulators of astrophysical phenomena that allow the reader to experiment with the phenomena. The later pages in a survey present the subject in greater and more mathematical depth. A path ends with research pages that describe current research projects and results in astrophysics.

The links at the top of each page are Home, which is the current home page of this site, Commentary, which is an index of short essays on topics loosely related to astrophysics, Surveys, which is the index of survey paths, Research, which is the index of research pages and the page leading to recent news items, Background, which is the index page for all background information on astrophysics, including survey pages, simulator pages, tables, bibliographic references, and lists of web resources, Previously, which is an index of previous home pages, and Site Info, which describes the site and its author, and gives contact information.

On the home page is found an addition link. This is the Store link, which leads to reviews of worthwhile books on astronomy and other relates subjects. Links on these pages enable the reader to buy these books from, which helps to financially sustain this web site.

Each Wednesday, a new issue of The Astrophysics Spectator is published that comprises a new home page, a new commentary, whatever news the author notices, and background, research, and simulator pages added to the survey paths. The home page acts as an index to the newly added pages. This site also has an RSS channel, whose link is given at the bottom of the right-hand column of this page.

March 30, 2005

This week I add the second of a series of three hydrogen fusion simulator pages to the web site. The new simulator added this week is a CNO hydrogen fusion simulator.

Last week I discussed how the hydrogen in a star is converted into helium-4 through the proton-proton fusion processes if the star contains little carbon, nitrogen, and oxygen or if its mass is that of the Sun or less. This week I discuss the carbon-nitrogen-oxygen (CNO) fusion processes, which convert hydrogen into helium-4 through a catalyst-like pair of cycles.

The CNO processes occur in massive stars of our epoch. For a sufficiently-high temperature, above about 20 million degrees Kelvin, the CNO processes convert hydrogen into helium-4 at a higher rate than do the PP processes. Because of the extreme sensitivity of the fusion rates on temperature, slight increases in temperature produce dramatic increases in energy generation.

The CNO processes constitute two cycles. In the dominant cycle, carbon is converted into nitrogen and then back into carbon as protons are absorbed and helium is released by the carbon and nitrogen nuclei. In the secondary cycle, nitrogen is converted into oxygen and then back into nitrogen, again accompanied by the absorption of protons and the release of helium nuclei.

Beside being a source of energy in massive stars, the CNO cycle is a source of nitrogen-14, the main constituent of our atmosphere. The early universe was composed principally of hydrogen and helium. The carbon, nitrogen, and oxygen we now see were created by several generations of massive stars preceding the birth of our Sun. These stars created carbon and oxygen from helium in the end stages of their lives. The nitrogen, however, was created from the carbon and oxygen through the CNO cycle of the following generations of massive stars.

The CNO simulator allows the reader to see the evolution of a gas of hydrogen and helium in which the CNO nuclear processes are at work. The simulator shows how nitrogen is created from carbon and oxygen. It also shows how small increases in temperature dramatically decrease the time it takes to consume all of the hydrogen in a star.

Two pages are added about the CNO Hydrogen Fusion Simulator. The first page contains the simulator and instructions on its use. The second page explains the results found with the simulator.

I have modified the page for the PP Hydrogen Fusion Simulator to match the pages for the CNO simulator. The original simulator page was simplified to a description of the simulator and an explain of its se. A second page has been added that explains the results found with the PP simulator.

All four pages for the CNO and PP simulators have been incorporated into the “Stars” survey path.

The Applet Control Guide has been updated to explain how to control a Java Swing slider from the keyboard.

Jim Brainerd


CNO Hydrogen Fusion Simulator In our epoch, massive main-sequence stars convert hydrogen to helium through the carbon-nitrogen-oxygen processes. The CNO Hydrogen Fusion Simulator simulates the complete conversion of hydrogen into helium over time through these processes. The reader can adjust the temperature and composition of the gas in the simulation. The simulator calculates the composition, power, and relative contribution of each CNO cycle to the helium production as functions of time. (continue)

Results from the CNO Hydrogen Fusion Simulator The CNO Hydrogen Fusion Simulator can be used to examine how the isotopes in the CNO cycle change with time and to test how the rate at which energy is generated changes with temperature. With this simulator, one can discover the relative ratios of carbon-12, nitrogen-14, and oxygen-16 that are generated through the CNO cycles. This page explains the results one finds with the CNO simulator. (continue)

Results from the PP Hydrogen Fusion Simulator With the PP Hydrogen Fusion Simulator, one can examine the effects of temperature and composition on the proton-proton fusion processes. At low temperature, helium-4 is created directly from helium-3. At higher temperatures, the helium-3 is converted into beryllium-7, which is then converted into helium-4. The various fusion processes come into play at different times during the fusion evolution of a gas. At high temperatures, the loss of energy through neutrino creation becomes important. These effects can be seen with the simulator. (continue)


PP Hydrogen Fusion Simulator The page for this simulator has been simplified to contain only a description of the simulator and instructions on its usage. A link to an explanation of the simulator's results is placed just above the simulator. (continue)

Applet Control Guide The guide has been updated to include instructions on controlling a Java Swing slider from the keyboard. The instructions of how to use the buttons have been collected under a new heading. (continue)


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