http://www.universetoday.com/61103/what-is-a-nebula/

​http://www.space.com/22471-red-giant-stars.html

https://heasarc.gsfc.nasa.gov/docs/snr.html

​http://www.space.com/23756-white-dwarf-stars.html

https://heasarc.gsfc.nasa.gov/docs/snr.html 

​http://utahscience.oremjr.alpine.k12.ut.us/sciber06/9th/stand_1/html/1_2a.htm 

http://www.docbrown.info/page03/3_54radio08.htm

​ http://www.britannica.com/science/gamma-ray-telescope and also electromagnetic spectrum 

Tarbuck, Edward J., Frederick K. Lutgens, and Dennis Tasa. Prentice Hall Earth Science. Needham, MA: Pearson/Prentice Hall, 2006. Print.



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