帮忙看一下这句话里的that(已用【】标出）指什么,是什么成分?

题目

帮忙看一下这句话里的that(已用【】标出）指什么,是什么成分?
The possibility that mass extinctions may recur periodically has given rise to such hypotheses as 【that】 of a companion star with a long-period orbit deflecting other bodies from their normal orbits,making some of them fall to earth as meterors and causing widespread devastation upon impact.

答案

感觉可能是指hypotheses,在进一步解释such hypotheses是怎样的