dark sirens

In recent years, cosmologists have been faced with a crisis: The universe is expanding, but no one can agree on how fast it’s moving away from us. That’s because different ways of measuring the Hubble constant, a fundamental parameter that describes this expansion, have produced conflicting results. But a single, lucky observation of what are known as dark sirens — black holes or neutron stars whose crashes can be picked up by gravitational wave detectors on Earth but remain invisible to ordinary telescopes — could help resolve this tension. As the cosmos expands, galaxies in the universe move away from … Read more