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These models treated a star as a sphere of gas held up against gravity by internal thermal pressure , and one of Eddington 's chief additions was to show that radiation pressure was necessary to prevent collapse of the sphere .
 person: Eddington
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 person: Eddington