astronomy homeworks ( Astronomy of the Universe AST 101) !!

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AST101Obsv.docx

First Observation:

All observed galaxies are red shifted (except for one). The exception is the Andromeda galaxy (M31) which is close enough to us that the mutual gravitational attraction overpowers the expansion.

Having already assumed that there is no preferred spot in the Universe, there is no reason to believe that our galaxy is at the center of the Universe. This means that we need to find a model that will allow for all of the galaxies to be moving randomly and yet their overall motion will be away from us.

Image result for cubic grid

The uniform expansion model can be thought of as placing a grid over the Universe and allowing the grid to expand. This results in every point in the Universe being further away from every other point.

This leads to two separate types of redshift. The physics principle involved is a Doppler shift for a wave. If the observed wavelength is shorter than it should be (shorter than the emitted wavelength) then the light is blue shifted. If the observed wavelength is longer than it should be then the light is red shifted.

The two classifications for redshift are derived from

1) Classical motion – motion through the environment

2) Cosmological motion – motion with the environment

If the motion of galaxies in the Universe were purely classical we would expect to see roughly half red shifted and half blue shifted. We would also expect the same degree of shift regardless of distance.

If the motion of galaxies in the Universe were purely cosmological we would expect to see all the galaxies redshifted. We would also expect galaxies that are further away to have larger red shifts.

What we actually observe is galaxy motion that is cosmologically dominated. This means that all of the galaxies (except Andromeda) are moving away from us and the further galaxies have a larger red shift.

Second Observation:

Several decades ago the US military was experimenting with microwaves. This led to a very interesting discovery with large astrophysical implications.

** In class number line example ** Develop the idea of an extremely small set that still has an infinite number of members.

This can be expanded to a thought exercise where I have a large sphere filled with photons. There are enough photons that they behave like an infinite set. This sphere is moved far enough away that it occupies an infinitely small portion of the sky. The result is that I have a system that behaves like an infinite number of photons residing in an infinitely small part of the sky.

The universe today is transparent and assuming the BBT is correct it should have started out being opaque. This requires that at some point in the past the universe changed from being opaque to being transparent.

What is the difference between intensity and energy as far as light is concerned? Energy is associated with wavelength and intensity is associated with photon count.

Low intensity microwaves are observed coming toward us from all directions. This is associated with the universe changing from being opaque to being transparent.

If the Big Bang Theory is correct then this would be expected.

Specifically, when the universe changed from being opaque to being transparent photons were released from all points in space and in all directions. The result of this is that regardless of where you are in the universe you will see background radiation coming toward you in the form of microwaves.

Third Observation:

What is a visible light map? Basically this is a star chart – it is a diagram that shows you where on the sky the visible light is coming from. This is something that allows you to determine which particular star, galaxy, etc. you are observing.

What then is a radio light map? As expected this would be a diagram that shows you where on the sky the radio waves are coming from.

Several decades ago (part II) astronomers began a project where they overlaid visible and radio light maps. The purpose of this is to determine what objects in the sky give off both types of radiation.

Several objects that were originally considered to be “small blue stars” were also demonstrated to be giving off radio waves. This was unexpected because stars were not thought to give off radio waves.

Now these objects are going to be studied in more detail. One of the first steps is to pass the visible light through a prism to gain information from the spectrum.

Doing this led to a very surprising result. Each of these “little blue stars” have a very large red shift. The next step becomes trying to determine if the red shift is classical or cosmological in nature.

If the red shift is classical, then it very well could be a nearby star but determining how it was accelerated to such a high rate of speed becomes an issue.

If the red shift is cosmological, the fact that it is very far away but still appears similar to stars in our galaxy means that it must be extremely large and intense.

The answer is that the red shift is cosmological in nature and the object is a forming galaxy. The formation process consists of gravity pulling the material together and the material coalescing to form the stars and everything else.

While gravity is pulling the material together, three measurable parameters are increasing:

1) Density

2) Temperature

3) Pressure

The outer regions of the forming galaxy will be at a lower energy. This means that the radiation given off there will show up as radio waves. The visible light being given off will come from locations nearer the center where the forming galaxy is more energetic.

This object is called a Quasar (often abbreviated QSR). This stands for Quasi-stellar radio source.

As the forming galaxy evolves, the outer regions will settle down first. This means that the outer regions will quit giving off light before the interior. Another way to think about this is as the galaxy formation process continues, the outer regions settle down and stop emitting radio waves while the interior continues to emit visible light.

This is the same object type, just more evolved. These are called QSO instead of QSR.

This is an abbreviation for Quasi-stellar object.