Black Holes 'Weigh' the Expansion Rate of the Universe express
Each merger of black holes produces gravitational waves — ripples in the fabric of the universe — predicted by Einstein and first detected with key contributions from Kip Thorne. Like strikes on a giant bell, they carry information about mass: most collisions cluster around three values — 10, 18, and 33 solar masses.
The expansion of the universe, discovered by Edwin Hubble, stretches this ringing, lowering the tones. By measuring the shift across 137 signals, scientists calculated the expansion rate: about 58 kilometers per second for every 3 million light-years (a megaparsec) — with an accuracy 21% better than previous methods. The main surprise: black holes of 33 solar masses were once exceptions, but now they play a loud note in the orchestra. The more mergers we record, the clearer the cosmic tuning fork sounds, and in the future, it might even allow us to hear the whisper of dark energy.
The lightest peak — 10 solar masses — is born from the collapse of an ordinary star. Black holes of 33 solar masses were considered a rarity, but now they are found more and more often, and they indeed set a powerful note in the symphony of mergers.