Usually, as they swim, they make clicking noises, and the resulting sound waves are reflected in an echo and travel back to them.
通常，当它们游泳时，会发出咔嚓的声音，所产生的声波会在回声中被反射回到它们身边。
Since x-rays travel at the speed of light, the echo indicates that an object fell into the black hole around 350 years ago.
因为X射线以光速运行，因此反射表明，大约在350光年前，有一个物质落入黑洞。
Echo has a great desire to travel the word, I wish for more people to learn from her smile.
我希望更多的人们从她的微笑中学到一些东西。
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