请问one作代词时与that的区别

rebecca_blue

请问：

"Astronomers at the Palomar Observatory have discovered a distant supernova explosion, one they believe to be of a type previously unknown to science."此句中的"one they believe ......"是否是同位语成分？

[此贴子已经被作者于2006-7-19 7:46:37编辑过]