Teacher:In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Teacher: Now, understand the problem? Solve this instance: Cygnus X-1 was the first X-ray source accepted as a black hole .
Student:
Cygnus X-1 ( abbreviated Cyg X-1 ) is a galactic X-ray source in the constellation Cygnus , and the first such source widely accepted to be a black hole .