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Above a certain mass determined by the Tolman–Oppenheimer–Volkoff limit , the process becomes runaway and the neutron star collapses to a black hole .
 Tolman–Oppenheimer–Volkoff
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Tolman–Oppenheimer–Volkoff