Suneeta Vardarajan · @Ms_Gravitas
12th Feb 2016 from TwitLonger
Why this observation of gravitational waves is also evidence for a black hole:
This observation of gravitational waves is DIRECT evidence of a black hole: after the two objects in the binary system merged to form one object, the gravitational waves detected showed characteristic decaying oscillations - the `quasi-normal modes'. Quasi-normal mode frequencies bear the signature of the final merged object (similar to the natural frequencies of a musical instrument). If the object is a spinning black hole (in contrast to a neutron star), the frequencies are characteristic numbers depending only on the final black hole's mass and spin. In a merger resulting in a black hole, one expects final decaying oscillations corresponding to the least damped frequency. This is what was observed, with the PRECISE numerical value of frequency for a spinning black hole with the mass and spin of the final object.
Black holes exist. Q.E.D :).