LIGO Detect Possible Second-Generation Black Holes with Extreme Spins

Late in 2024, the LIGO-Virgo-KAGRA observatories observed two strange gravitational-wave signals that suggest the existence of so-called second-generation black holes. The rapidly spinning black holes were in collisions, GW241011 and GW241110. The majority of the black holes spin, but in GW241110, one of the black holes has rotated against its orbit, and this is a twist. The bigger hole was rotating extremely fast in GW241011. Such extreme spins imply that the huge holes could have been created as a result of the previous black hole mergers.

Unusual Black Hole Mergers

According to a paper published in The Astrophysical Journal Letters, in GW241011 (Oct 2024), LIGO-Virgo-KAGRA detectors observed a merger of black holes with masses around 17 and 7 times the Sun's mass, with the larger one spinning extremely fast. In November 2024, the detectors saw GW241110, the merger of black holes of about 16 and 8 solar masses. Remarkably, in this case, one black hole's spin was tilted opposite its orbit—a first-of-its-kind observation.

Evidence for Second-Generation Black Holes

LIGO scientists note that both events provide “tantalizing evidence” of earlier black hole mergers. Hierarchical models predict that second-generation black holes should be heavier, spin faster, and have misaligned axes, matching the extreme mass ratios and tilted spins seen in GW241011 and GW241110. Astrophysicists suggest such repeated mergers occur in dense star clusters, where multiple collisions are likely. According to the collaboration, these observations “add an important new piece to our understanding” of black hole phenomena. These results offer rare insight into how some black holes can grow by merging with others.