The Pillars of Creation, an iconic image photographed by the Hubble Space Telescope. It exists in the Eagle Nebula.
Source: http://en.wikipedia.org/wiki/File:Eagle_nebula_pillars.jpg
Source: http://en.wikipedia.org/wiki/File:Eagle_nebula_pillars.jpg
Variable Stars, Pulsars and More
So far, we have focused on the basic stellar evolution of most stars, without looking at some of the most exotic and interesting star types. Now, we turn to them.
First, there are the variable stars.. These stars include T - Tauri stars, RR Lyrae stars, and classic Cepheid variable stars. These three stars pulsate due to changes in the thermo - gravitation equilibrium. T - Tauri stars tend to be cooler and dimmer than RR Lyrae and Cepheid stars. The latter two tend to be extremely similar, Cepheid variables generally only having a longer period. Both the RR Lyrae and Cepheid variables exist in the instability strip, while T - Tauri stars are located lower and further to the right (near the Sun). In addition T - Tauri stars are pre - main sequence, extremely small and have intense emission lines. It is believed that the Sun was once a T - Tauri star.
First, there are the variable stars.. These stars include T - Tauri stars, RR Lyrae stars, and classic Cepheid variable stars. These three stars pulsate due to changes in the thermo - gravitation equilibrium. T - Tauri stars tend to be cooler and dimmer than RR Lyrae and Cepheid stars. The latter two tend to be extremely similar, Cepheid variables generally only having a longer period. Both the RR Lyrae and Cepheid variables exist in the instability strip, while T - Tauri stars are located lower and further to the right (near the Sun). In addition T - Tauri stars are pre - main sequence, extremely small and have intense emission lines. It is believed that the Sun was once a T - Tauri star.
An HR - Diagram showing T - Tauri stars pictured near the Sun, and the instability strip circled.
Source: https://www.eso.org/public/outreach/eduoff/cas/cas2002/cas-projects/bulgaria_v1751_1/image11.jpg |
V8383, a variable star of type L - Supergiant
Source: http://en.wikipedia.org/wiki/File:V838_Monocerotis_expansion.jpg |
Pulsars and magnetars are both stars with intense, powerful magnetic fields. The primary difference being that pulsars spin while spewing a beam of radiation, while magnetars are simply neutron stars with extremely powerful magnetic fields. The rotation of pulsars mean that their beam of radiation only reaches Earth periodically, which can be used to calculated their period of rotation. This rotation can be anywhere from 1000s of rotations per second to single rotations per hour, depending on the age of the star. This motion generally comes fro the conserved angular momentum from the star's earlier days. This led to early discovers to believe that pulsars may, in fact be alien communication! Magnetars, are also quite interesting. They have some of the strongest magnetic fields ever seen in the universe, which heat up the surface to tens of millions of degrees Celsius.
A pulsar showing both intense magnetic field lines, and the jets of electromagnetic radiation being directed by those fields. As this is a still rendition, the spin of the pulsar is not shown.
Source: http://www.theepochtimes.com/n2/images/stories/large/2012/02/19/230227main_Pulsar1.jpg
Source: http://www.theepochtimes.com/n2/images/stories/large/2012/02/19/230227main_Pulsar1.jpg
Thus far, we have seen the proton - proton chain, CNO cycle, and triple alpha process, all used by stars for fusion. However, stars also fulfill one other important job by using a different set of nuclear processes. Elements past iron require extreme conditions to create, and stars can function as factories for these using the r - process and the s - process. The r - process creates heavy elements during a supernova, while the s - process takes heavy elements to create heavier elements by neutron capture in asymptotic giant branch stars. The r - process is also referred to as rapid neutron capture because it involves a sudden influx on neutrons attacking a nucleus, while the s - process is refereed to as slow neutron capture since it uses stable, step by step fixation.