55361
Observations have shown that the pulsar 's orbit is gradually contracting , which is generally understood to be evidence for the emission of energy in the form of gravitational waves , as described by Einstein ’s theory of general relativity , causing the pulsar to reach periastron slightly early .
 Einstein
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Einstein