text:   hole",6,"[""In work led by @CollinCapano we find support for a sought after sub-dominant mode in the 'ringdown' of GW190521. This enables a test of the nature of the final black hole and suggests limits on the mass ratio of the initial binary.\n\n<LINK> <LINK>"", ""General relativity predicts that for a Kerr black hole (spinning, no charge) if it is perturbed, such as when resulting from the merger of two progenitor black holes, it will emit gravitational radiation during this 'ringdown' with a predictable discrete spectrum of frequencies."", 'A key principle is that spectrum of these modes only depends on the total mass and spin of the black hole. (the relative amplitudes may however depend on the initial system).', ""By comparing the observed modes and the prediction from General relativity, we can test the nature of the final black hole and look for signs of new physics. We find the observed signal is very consistent with what you'd expect from a perturbed Kerr black hole. https://t.co/EQAHsF6AGa"", 'The presence of one particular mode also indicates that the original system was unlikely to have been made of equal mass black holes (NR simulations suggest that unequal masses are required to excite this mode). This allows one to predict what the mass ratio may have been. https://t.co/JvZoDqpflt', 'GW190521 has been somewhat of mystery for the gravitational-wave community. It is the highest mass merger observed to date, there is a possible EM flare observed in coincidence, and several studies have suggested the merger may be eccentric. Likely mysteries remain!']",21,05,1517