##Notes-Week2.txt

==========================WEEK-2============================

## Every different type of object emits radiation of 
     different frequency.(see the image "big data make things slow.png")

## Astronomers uses astronomical telescopes and many 
    optical devices to allocate these frequencies of 
    different scale.

## In contrast, radio emission, at centimeter to meter 
     wavelengths, occurs when, for example, electrons are
     accelerated in magnetic fields, and can show us when 
     massive shocks are occurring in space.

## Here's an example of what you get when you 
     find a match in optical and radio, and combine  
     that information together.Hercules A, 
     a radio galaxy 643 megaparsecs, or 2,100 million 
     light years away. Remember, in cosmological terms, 
     that makes it a pretty near neighbor.
     You can clearly see the core of the galaxy 
     where the supermassive black hole is located,
     the powerful jets transporting energy to the outskirts 
     of the galaxy and beyond. And the massive lobes of 
     old radio emission from previous cycles of activity.
     In the optical image, you can see the stars that 
     make up the elliptical galaxy 3c348.(see image "hercules.png")

## Our eyes can only detect the lights of visible
     region of em spectrum.

## Galaxies are not just made up of stars, they also
     contain a lot of gas and dust, and at the heart of 
     all large galaxies, a supermassive black hole, millions
     or even billions of times the mass of our sun, squeezed 
     down into a space smaller than our solar system. 
     Although very small compared with the scale of an 
     entire galaxy, these black holes can have a huge 
     impact on the galaxy's growth and formation. 
     In cases where there is a lot of gas in the central region
     of the galaxy, this material can be accreted on to the
     black hole via an Accretion Disk, releasing a lot of 
     energy in the process. This is what we call, an 
     Active Galactic Nucleus, or AGN. The radiation 
     produced by the AGN is so bright that it can outshine
     the entire galaxy, producing far more energy 
     than all of the galaxy's stars combined. 
     The accretion process can also form huge
     jets of strong magnetic fields emanating out from 
     around the black hole. And fast moving electrons
     spiraling around these magnetic fields, produce huge
     quantities of radio emissions. These radio jets can 
     grow to enormous sizes, sometimes extending far 
     beyond the galaxy to be millions of light-years across.
     They can also provide information on the past 
     activity of the central black hole.

## If we create some arrays of random values and 
     cross-match them, increasing the number of values 
     in each array, each time, we end up with a plot like this. 
     The x-axis shows the number of points we put in 
     each catalogue. And the y-axis shows the number of
     milliseconds the code took to run. For 100 galaxies, 
     my program takes roughly 50 milliseconds. For 1,000 
     galaxies, my program takes roughly 5,000 milliseconds. 
     And for 10,000 galaxies my program takes roughly 
     500,000 milliseconds. We could keep going, but I got
     bored waiting on the script to run. It doesn't matter 
     because we can already see a clear trend. When we 
     increase the number of galaxies in each catalogue by 
     a factor of ten, the time the program takes to run 
     increases by a factor of 100