It is thought that any acceleration of massive objects in the universe will generate gravitational waves. Black hole and neutron star collisions, supernovae and galactic mergers are all thought to be huge sources of gravitational waves; if we can somehow detect and, indeed, map them we could reveal some of the most massive objects and most energetic events in the cosmos.
ANALYSIS: Faster-Than-Light Neutrinos Caused by Loose Cable?
The theoretical basis for gravitational waves spawn from general relativity equations that were formulated by Albert Einstein over 100 years ago. Although there is indirect evidence of gravitational waves carrying away energy from orbiting bodies (through extended observations of binary pulsar and white dwarf systems), the detection of the extremely slight impact of the propagation of gravitational waves that are hypothetically washing though our planet has been maddeningly difficult to achieve.
The LIGO stations use extremely fine-tuned laser interferometers to detect the passage of gravitational waves (that can be imagined as ripples in spacetime, much like the ripples that propagate across the surface of a pond) and only weeks before Krauss' original tweeted rumor had embarked on a new phase of sophistication, called Advanced LIGO.