Gravitational Waves

Gravitational waves are a form of radiation predicted by Einstein’s theory of general relativity. Created by the movement of mass and energy, they are ripples in space and time, and travel at the speed of light. They are expected to be the dominant form of energy emission from what are among the most exotic objects in the universe: black holes. The existence of gravitational waves has been inferred from precise measurements of the decay of the orbit of the binary neutron star system PSR B1913+16, also known as the Hulse-Taylor binary pulsar. Although this effect of gravitational radiation has been observed, gravitational waves themselves have never been detected until now.

Several groups, world-wide, are collaborating on the construction and operation of kilometer-scale laser interferometers that are expected to observe gravitational waves directly in the next few years. Among other things, these observations will provide the first experimental tests of general relativity in the strong-field regime, teach us about the properties of nuclear matter at extreme densities and about the end stages of stellar evolution.

Researchers at CITA are members of the LIGO Scientific Collaboration, a US-led effort operating the two Advanced LIGO gravitational-wave observatories in Louisiana and Washington States. Data sharing agreements also provide CITA researchers access to data collected from the French-Italian Virgo antenna (currently undergoing upgrades) and the German-UK GEO600 antenna.

CITA researchers are leading the development of the low-latency analysis pipeline for quickly identifying the collisions of compact-objects like black holes and neutron stars in the data collected from LIGO antennas. With this technology it will be possible to alert electromagnetic transient telescopes so that coordinated observations of neutron star collisions will be possible using gravitational-wave, optical, and radio telescopes to learn the most about these exotic events.

CITA researchers also members of the SXS Collaboration and numerically model the gravitational waveforms expected from compact object mergers, as described in the section “Black holes, neutron stars & white dwarfs.” These theoretical models play a crucial role in interpreting the gravitational waves detected by Advanced LIGO and other observatories.


How Black Holes Collide

A mathematically and computationally accurate model made using Einstein’s GR equations of a binary black hole collision producing  gravitational waves.  The large black hole is spinning, and is three times the mass of the smaller black hole.  Their orbital decay and final collision produces crushing gravitational waves that sweep outward.

The simulation’s colours denote the following:
(a) Yellow-red-green:  Intrinsic scalar curvature of the apparent horizon.
(b) grey lines: trajectories of the centers of the apparent horizons
(c) The plane is the **instantaneous** orbital plane, so its motion indicates precession.   This plane is shown with two different color codings:
(c1) far away in black-blue-white:  The magnitude of the Weyl-Scalar r*Psi4.
(c2) near the black holes in purple-white:  The lapse function.

Binary Neutron Stars with Arbitrary Spins in Numerical Relativity
Nick Tacik, Francois Foucart, Harald P. Pfeiffer, Roland Haas, Serguei Ossokine, Jeff Kaplan, Curran Muhlberger, Matt D. Duez, Lawrence E. Kidder, Mark A. Scheel, Béla Szilágyi

Accuracy and precision of gravitational-wave models of inspiraling neutron star — black hole binaries with spin: comparison with numerical relativity in the low-frequency regime
Prayush Kumar, Kevin Barkett, Swetha Bhagwat, Nousha Afshari, Duncan A. Brown, Geoffrey Lovelace, Mark A. Scheel, Béla Szilágyi

Improvements to the construction of binary black hole initial data
Serguei Ossokine, Francois Foucart, Harald P. Pfeiffer, Michael Boyle, Béla Szilágyi

Likelihood-Ratio Ranking Statistic for Compact Binary Coalescence Candidates with Rate Estimation
Kipp Cannon, Chad Hanna, Jacob Peoples

Numerical relativity reaching into post-Newtonian territory: a compact-object binary simulation spanning 350 gravitational-wave cycles
Bela Szilagyi, Jonathan Blackman, Alessandra Buonanno, Andrea Taracchini, Harald P. Pfeiffer, Mark A. Scheel, Tony Chu, Lawrence E. Kidder, Yi Pan
Phys. Rev. Lett. 115, 031102 (2015)

Turbulent Black Holes
Huan Yang, Aaron Zimmerman, Luis Lehner
Phys. Rev. Lett. 114, 081101 (2015)