Gravitational waves!! Only recently detected even indirectly, they offer some evidence to support Einstein’s theory of relativity from the early twentieth century. The theory states that dense, heavy objects (like Earth, for example) distort space-time in the same way a marble would bend a normally flat stretch of fabric. When two extremely dense objects (such as neutron stars or black holes) orbit one another, then, they swirl space time as depicted in the image below. These ripples from massive objects that radiate across space-time are known as gravitational waves.
Gravitational waves were first detected indirectly in the 1900s, and directly detected finally in 2016. Although the actual observation itself was made in late 2015, rigorous statistical analysis was required prior to actual confirmation of an observation in early 2016. The detection came from a binary system of two black holes, each roughly thirty times the mass of the Sun. As the two finally merged into a single black hole, the system released powerful ripples through space-time. In the following two years, the observatory detected three more instances of gravitational waves, all from collisions of binary black hole systems.