61369
This occurs because the pair either forms a binary star ( i.e. a binary system of stars in mutual orbit , gravitationally bound to each other ) or is an " optical double " , a chance line-of-sight alignment of two stars at different distances from the observer .
 binary star
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 binary star