上面的推理不对,文章中第二段星球的情况是特殊的 From its speed, they calculated that the core’s density is more than 40 times the density estimated for any other galaxy. 因此如果中心是a cluster of stars 才会造成torn apart的。。。不是a cluster直接就是torn apart. 而a选项恰恰好支持了那个观点,说明不是所有的中心都会被排除是a cluster of stars.
第一段最后一行the concentration in M87 might be a cluster of a billion or so dim stars.
From its speed, they calculated that the core’s density is more than 40 times the density estimated for any other galaxy.If the center of NGC 4258 were a star cluster, the stars would be so closely spaced that collisions between individual stars would have long ago torn the cluster apart.