Model 4: Active Galaxies

Active galaxies are referred to as such because their supermassive central black holes are still actively absorbing and emitting matter from their accretion disks. 

Matter swirling around the accretion disk collides with other matter and loses energy. This loss of energy causes the pull of the blackhole to dominate the fling of the matter. The matter falling into the blackhole is so hot that it becomes ionized. When this ionized matter crosses the blackhole's extremely powerful magnetic field, it follows the lines in the form of synchrotron radiation. This radiation is emitted from the north and south magnetic poles of the blackhole. Synchrotron radiation has a continuous spectrum and is very energetic. This radiation is emitted in the form of jets that can span trillions of light years before ending because of a collision with interstellar medium. 

Active galaxies are only viewed at extreme redshifts because of their prevalence during the beginning of the universe. This prevalence is because during the early universe all of the matter was closer together and hotter--these qualities are prime for blackholes that absorb their accretion disk material. It is likely that our galaxy in the past was active. 

The Unified Theory of Active Galaxies explains the different phenomena that one can observe about Active Galaxies. 

1. Blazars are active galaxies viewed looking at the jets straight on. One would see a very bright, very redshifted "star". 

2. Quasars are active galaxies viewed slantwise from the jets. One would see a very bright, very redshifted "star" as well as fuzz surrounding the star. The fuzz spectra would have absorption lines and the bright jet would show emission lines like synchrotron radiation. 

3. Radio galaxies are active galaxies viewed from the side. One would see a galaxy with two high energy jets bursting from its sides. 

-Seyfert galaxies are radio galaxies seen from an angle that exposes both jets but one may be shortened. 

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 2: the HR diagram

The HR diagram is a graph with star temperature (K) on the x axis and star luminosity (sun luminosity) on the y axis. The graph was created by plotting data collected by male scientists. However, the graph and trends noticed in the graph were discovered by female scientists. 

By plotting the stars data one learns that luminosity relates to temperature in a way that creates three major star classification categories: the Main Sequence stars (like our Sun), the Giant stars (middle aged), and the White Dwarfs (dying stars). Within these categories there are others (see supergiants and brown dwarfs).

Understanding the HR diagram led scientists to develop theories about the lifetimes of stars despite the fact that no one human can study a full lifetime of a star. 

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!

shooting across the atlanta skyline

i went out last night into atlanta to meet a friend for dinner and a movie; it was good to get out of decatur for a few. despite what has always been my experience with meteor showers (i don't actually see them), i am constantly on the look out for their immediate presence in my nightlife. while driving down ponce i saw what looked like a meteor inch down into the darkness. i'm sure it was a firework or gunshot or something, but it was terribly beautiful. 

i need to ask dr. lovell what she wants from these blogs, more specifically. so far i've just been going on.

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!