About how many solar masses was the final black hole formed in GW150914? The remnant had a mass of about 62 solar masses.
GW150914 was the first directly detected gravitational-wave event and the first observed merger of two black holes. LIGO detected the signal on September 14, 2015, and the discovery was announced in February 2016. The waveform showed two black holes spiraling together, merging, and settling into a spinning final black hole.
The original black holes had estimated masses of about 36 and 29 Suns. Their total was therefore roughly 65 solar masses, but the final remnant was lighter because about three solar masses’ worth of mass-energy was radiated away as gravitational waves during the merger. The result was a black hole of approximately 62 solar masses, with published uncertainty ranges around that estimate.
The number is not a direct visual weighing. It is inferred by matching the measured gravitational-wave signal to predictions from general relativity. A common mistake is to choose 36, which was approximately the mass of the heavier pre-merger black hole, rather than the mass of the post-merger remnant. GW150914 occurred more than a billion light-years away, yet its spacetime ripples were measurable at both LIGO detectors.