(See description below)

Click for movie
Black Holes Merging (simulated picture)

The strrong graviational field of the two black holes bends the light of stars behind them so they are seen distorted around the black holes.  Without the black holes present, the stars would appear as shown below.

Click on the video at the very bottom  for a movie simulating the black holes merging.  In this movie, the black holes are near us, in front of a sky filled with stars and gas and dust. The black regions are the shadows of the two black holes: no light would reach us from these areas. Light from each star or bit of gas or dust travels to our eyes along paths (light rays) that are greatly bent by the holes' gravity and by their warped spacetime. This is called "gravitational lensing." Because of this gravitational lensing, the pattern of stellar and gas/dust images changes in fascinating ways, as the black holes orbit each other, then collide and merge.
The ring around the black holes, known as an "Einstein ring," arises from all the stars in a small region directly behind the holes; gravitational lensing smears their images into the shape of a ring.
The gravitational waves themselves would not be seen by a human near the black holes (though they would be felt!) and so do not show in this video, with one important exception: The gravitational waves that are traveling outward toward the small region behind the black holes disturb that region’s stellar images in the Einstein ring, causing them to slosh around in the ring, even long after the collision. The gravitational waves traveling in other directions cause weaker, and shorter-lived sloshing, everywhere outside the Einstein ring.
Source

On September 14, 2015 gravity waves were detected that resulted from the merger of two black holes 1.3 billion light-years away.  One black hole had a mass 29 times that of the mass of our sun, and the other 36 times the mass of the sun.  Just before they merged, they were orbiting each other at half the speed of light and radiating gravity waves with a power 50 times greater than the light output of all the stars in the universe. The energy lost amonted to 3 masses of the sun (using E = mc2).  These waves were detected by two LIGO sensors on Earth—one in Louisiana, and the other in Wahington state.  The waveform received is shown below (top).  The amplitude of the wave is very small—1/1000 of the diameter of a proton.  This distance, divided by the length of the 2.5-mile tunnel for the laser beam, gives the strain of just 10–21.  The waveform, converted to sound, sounds like this. (The first "chirp" is in vicinity of 150 Hz; the second chirp is the same sound raised in frequency by a factor of 10 to be heard better.)  The waveform agrees well with that predicted by theory (bottom waveform below).  For detailed information read this Physics Review Letter.
Source.