LIGO ‘hears’ space-time ripples produced by black-hole collision.
Conveyed by these gravitational waves, an energy 50 times greater than that of all the stars in the universe put together vibrated a pair of L-shaped antennas in Washington State and Louisiana known as LIGO on Sept. 14.
If replicated by future experiments, that simple chirp, which rose to the note of middle C before abruptly stopping, seems destined to take its place among the great sound bites of science, ranking with Alexander Graham Bell’s “Mr. Watson — come here” and Sputnik’s first beeps from orbit.
In physics, gravitational waves are ripples in the curvature of spacetime which propagate as waves, travelling outward from the source. Predicted in 1916 by Albert Einstein on the basis of his theory of general relativity, gravitational waves transport energy as gravitational radiation. The existence of gravitational waves is a possible consequence of the Lorentz invariance ofgeneral relativity since it brings the concept of a limiting speed of propagation of the physical interactions with it. By contrast, gravitational waves cannot exist in the Newtonian theory of gravitation, which postulates that physical interactions propagate at infinite speed.
Prior to the direct detection of gravitational waves, there was indirect evidence for their existence. For example, measurements of the Hulse–Taylor binary system suggest that gravitational waves are more than a hypothetical concept. Potential sources of detectable gravitational waves include binary star systems composed of white dwarfs, neutron stars, and black holes. As of 2016, various gravitational-wave detectors are under construction or in operation, such as Advanced LIGO which began observations in September 2015. In February 2016, the Advanced LIGO team announced that they had detected gravitational waves from a black hole merger.