Readers discuss a new type of black hole merger, warm-bloodedness and more

Twisted sisters

Two black holes merged while spinning in nearly opposite directions, suggesting that they were born in different places and found each other late in life, James R. Riordon reported in “New type of black hole merger found” (SN: 8/27/22, p. 13).

Reader Van Snyder wondered if the reason for the black holes spinning in nearly opposite directions is that some sort of collision flipped the parent star of one of the black holes.