# Gravitational Waves

Changes in a gravitational field propagate as gravitational radiation. The merger of two compact objects—black holes or neutron stars—results in the release of a phenomenal amount of energy in gravitational waves. These waves have recently been detected by two observatories, LIGO in the United States and Virgo in Italy.

Information about the merging binary is encoded in the gravitational radiation. By comparing the detected signal to the predictions of general relativity, we can learn about the black holes or neutron stars that created the radiation. The equations of general relativity, however, are very complicated and nonlinear. We know only a few analytical solutions to these equations, and none for merging binaries. Therefore, we use numerical techniques, or numerical relativity, to solve the equations for merging binaries on large supercomputers. These solutions allow us to predict the spectrum of the gravitational waves.

New gravitational wave detectors are being planned. KAGRA, a new detector in Japan, will soon join LIGO and Virgo in the search for gravitational waves. LISA is a space-based detector that will be launched in the middle of the next decade.

### Gravitational Waves with Dendro-GR

Many black hole binaries have in black holes with nearly equal masses. Some binaries, however, may form through dynamically, in which case the masses may be very different. We are exploring gravitational waveforms from binaries with large mass ratios

\[ q = \frac{m_1}{m_2}, \qquad {\nm for}~m_1 \ge m_2. \]

This figure shows the gravitational waveform, technically the wave quantity \( {\nm Re}\ \psi_4\), for a \(q=16\) binary.