Model 3: the lifetime of a star

Lifetime of a star in list form!

1. Cool interstellar medium collides with other interstellar medium due to density waves in the spiral arms of our galaxy.

2. This blob of medium gains enough mass and begins to compress.

3. Spin of medium and compression combined with conservation of angular momentum cause the blob of gas to spin faster and faster as it shrinks. 

4. Pressure builds in the center of the blob as matter is pressed and condensed. 

~this entire process can take from 10,000 to 1,000,000 years depending on the mass of the star~

5. The rotation of the blob (protostar) and centrifugal motion cause an accretion disk (protoplanetary disk) to form around the protostar. 

6. The protostar continues to shrink and spin until the pressure and temperature inside its core are high enough to spark the fusion of hydrogen into helium. 

7. Jets form at the poles of the protostar along the magnetic field lines and heat up the surrounding gas and accretion disk. 

8. The accretion disk is blown away by the jets. 

~except for protoplanets and planetoids which remain due to their gravity~

9. The star is now on the main sequence, technically. (ZAMS)

10. Depending on the age of the star, it spends some years on the main sequence. 

11. The star cools and its hydrostatic equilibrium is put off balance. The radiation from the core stops pushing against the pressure of the outer layers and the core contracts. 

12. The outer layers cool and expand so the star because more luminous.

13. The core contracts until shell hydrogen fusion and helium fusion begin.

~this can occur in a "flash" for lower mass stars or in a gradual process for higher mass stars~

14. The star is now a giant star and spends time fusing helium.

15. If the star is very massive it will continue this shrinking and growing process as it fuses heavier and heavier elements. 

16. If the star is massive, when it finishes fusing iron, it will supernova and its remnant star will be a white dwarf (this white dwarf could turn into a neutron star or a black hole).

17. If the star is less massive, when it finishes fusing helium or carbon, it will simply cool off and its outer layers will expand creating a planetary nebula. 

Model 1: The Sun and the Proton-proton Chain

Studying the Sun provides scientists with a plethora of data as well as an idea of how all stars are born, live, and die. Despite all of the information gained from observation, there are parts of the Sun (most of its interior) that scientists only postulate about based on data from models of the Sun. Combining what we do know (surface temp, chemical composition because of spectra, mass because of Newton, and the temperature required in order to fuse hydrogen protons into helium protons) we have created a model for the insides of the Sun. 

The layers of the sun from inside to outside: core, radiative, convective, photosphere, chromosphere, corona. 

Core and radiative zone are where fusion takes place. The pressure and temperature are right here. 

Convective zone is mostly plasma made up of hydrogen. 

Photosphere and chromosphere are the two upper most layers of the Sun. The chromosphere is hotter than the photosphere.

The corona is the wispy highest layer. It is made up of very hot, ionized gas. However, if you were to be inside of it (somehow without dying from the lack of oxygen, etc etc) you wouldn't be immediately burned. Imagine, for example, the way the hot air feels as you open the oven after you've been cooking something. You feel the heat and you could identify that it is very hot, but you are not burned the same way you would be if you touched the metal inside the oven. 

Inside the core of the Sun, it is so hot that the electrons associated with the protons of the hydrogen atoms are no longer bound to them. The electrons are in a free state. Two hydrogen protons bond together, and then those two bond with another to form a helium atom. The interesting part (okay, one of the interesting parts) comes when you look into the mass of the atoms before and after. The total sum of the protons after added up is less than before when they were single hydrogen protons. A tiny bit of mass is gone! What happened to it? It left in the form of a neutrino, a positron, and a gamma ray. By the time the gamma ray makes it from the Sun's core to the Sun's surface, it has lost energy and is viewed as visible light. 

Neat!

christening post

so begins my journey into astronomical (and everything else) blogging--with jeff buckley as my musical companion. 

i'll admit my motivation for creating this blog is selfish in nature; in my galaxies and cosmology class we have been instructed to post a blog each time we approach a new "model" during the lecture and readings. we spent a week in class reviewing the more mathematical aspects of the intro course (kepler's laws, newton's form of kepler's third law, electromagnetic radiation and its relation to spectra and temperature, wien's law, the stefan-boltzmann law, and the doppler shift). we start this week on the chapter about the sun. 

get ready for sun models!