The Laser Interferometer Gravitational-Wave Observatory (LIGO), which "heard" gravitational waves from a pair of colliding black holes back in September and confirmed it this past February, has registered a second such event and scientists confirmed it today.
LIGO actually received the signal on Dec. 26, but it takes time to process the readings and confirm that what it records are actually gravitational waves and not some other phenomenon. The pair of back holes were 1.4 billion light years away, about the distance of the first colliders the instrument detected.
Modern theories of physics suggest that every collision between two objects produces gravitational waves, but the waves are so weak that when normal objects hit they can't be detected. Only when something with the mass of a super-dense black hole hits something equally massive can the gravity waves actually register, and even then LIGO scientists have to do a lot of work to sort out the signal from background "noise" that can mask it.
As the story at the link notes, the pattern of the waves showed that one of the black holes involved in the smash-up was spinning -- something that it had been thought LIGO could detect but which had yet to be proven.
In addition to offering yet more proof of general relativity, the new measurements will allow astronomers and cosmologists to start guessing how often black holes run into each other and to continue to fine-tune the instrument. The next scheduled test of the device is set for the first presidential debate of the regular election season, when Donald Trump's ego will collide with Hillary Clinton's un-likeability. Scientists have said they will probably have the LIGO on its lowest setting to avoid burning out the detector when objects of that much mass collide.