4498
Once the core hydrogen is exhausted in 5.4 " billion years , the Sun will expand into a subgiant phase and slowly double in size over about half a billion years .
 astronomical object: subgiant
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 astronomical object: subgiant