Kari Alison Hodge's Dance Your PhD - The Search for Gravitational Waves in LIGO Data from the Coalescence of Two Black Holes

Hi! I am a graduate student at Caltech and this video is my entry in the 2013 "Dance Your PhD" contest. An introduction to my PhD research is below, as is some background regarding the vocal tracks in the video.

The coalescence of a pair of black holes produces ripples in spacetime known as gravitational waves. The coalescence is marked by three phases: 1) the "inspiral", when the two black holes are orbiting one another and the distance between them gets smaller and smaller; 2) the "merger", when the two black holes join to become one; 3) and the "ringdown", when the final black hole releases its excess energy, much like what happens when you ring a bell. The ripples in spacetime, which contain information from these three signature phases of coalescence, travel outward from the black holes at the speed of light. LIGO (The Laser Interferometer Gravitational-Wave Observatory) is designed to detect these gravitational waves, which stretch and squeeze spacetime as they pass by the detectors' sites in Louisiana and Washington state, causing the arms of a detector to alternate between getting shorter and longer. However, other things can happen inside the detector and in its environment that can trick scientists into thinking LIGO data contains a signal from two black holes. Events as different as an airplane going by or a glitch in any of the electronic control systems can mimic a true astrophysical signal. Comparing what is seen in the detector's gravitational-wave data to the theoretical waveform from a pair of coalescing black holes is not sufficient in order to distinguish an astrophysical signal from a glitch. We must also use the information from various sensors, in and around the detector, to confidently identify the signal. Combining all this information allows us to mistake fewer glitches for astrophysical events, which effectively increases the volume of space we can "hear".

The coalescence of two black holes is actually very well-suited to a musical interpretation - the frequency of the produced gravitational waves is in the audio band. As the inspiral progresses and the black holes get closer together, the signal sweeps upward in both frequency and volume (this is known as a "chirp"). The attentive listener can hear the actual chirp (created by a computer simulation, as no gravitational waves have yet been detected) from the inspiral of two black holes during a couple key moments of my video. The vocal track over the black hole dance and the corresponding data also follows this progression of low to high, during the inspiral phase. During the ringdown, the vocal track is composed of a superposition of several frequencies, which is another direct analogy to what is physically happening. Note that most physical disturbances produce a ringdown effect in the disturbed object (imagine hitting a bell with a hammer), making them difficult to distinguish from a signal from the coalescence of two black holes.

The dance during the closing credits (led by my thesis advisor) is the official LIGO dance - as the gravitational wave passes by, one arm of the detector/dancer gets shorter and the other arm gets longer in an alternating manner!

Visit www.ligo.org for more! And even more musical LIGO fun here: http://www.youtube.com/watch?v=kapaztyPFVI&feature=youtu.be