In the quest to detect gravitational waves, there are a number of obstacles that — no matter how hard we try — continue to stand in our way. Since 2015, with the advent of first the advanced LIGO detectors and then later, the Virgo detector, humanity has directly detected gravitational waves from a particular set of sources: merging stellar-mass black holes, merging neutron stars, and (perhaps) merging black hole-neutron star pairs. More recently, a different technique, leveraging pulsar timing, has discovered a cosmic “hum,” or the sum of all background gravitational wave signals with a much longer timing period.
Nevertheless, there are still limits to what we can do with current technology.