What did the first detection GW150914 by LIGO confirm about black holes?

• A. LIGO is a gravitational-wave detector; GW150914 was the first direct detection of gravitational waves from a binary black hole merger.
• B. LIGO is a radio telescope; GW150914 detected gamma rays.
• C. LIGO is a space-based interferometer; GW150914 was a neutron star merger.
• D. LIGO detects gravitational waves only from core-collapse supernovae.

Answer: (D)

The main idea being tested is that gravitational waves from a real black-hole merger can be observed directly, proving that such mergers occur and produce detectable spacetime ripples. The first detection, GW150914, showed LIGO can observe these waves as a distinct chirp: the signal starts at a lower frequency and grows in both frequency and amplitude as two black holes inspiral, merge, and settle into a single black hole. The waveform matched the predictions of general relativity for a binary black-hole system, including the rapid merger and the characteristic ringdown that follows. This event demonstrated that binary black holes exist, do merge, and radiate a tremendous amount of energy in gravitational waves—about a few solar masses’ worth—into the cosmos. It also confirmed that the signal was genuinely coming from space, observed at two separate detectors with consistent timing, reinforcing the interpretation as a real gravitational-wave event rather than local noise.

The other statements don’t fit because LIGO is a ground-based gravitational-wave detector, not a radio telescope or space-based instrument, and the signal GW150914 came from a binary black-hole merger, not a neutron-star inspiral. Gravitational waves detected by LIGO come from a variety of sources, not only core-collapse supernovae.