Simulation of two black holes

Simulation of two black holes merging into one
Image Courtesy Caltech/MIT/LIGO Laboratory; SXS (Simulating eXtreme Spacetimes) project

Canadians Contribute to Gravitational Wave Discovery

University of Toronto, Perimeter Institute play key roles in major confirmation of Einstein's equations


After searching for a century, the final prediction of Einstein’s 100-year-old Theory of General Relativity has been proven: when massive objects collide, such as two black holes, some of their mass is converted into energy in the moments before they merge, causing ripples in the fabric of spacetime.

This discovery has broad implications for our understanding of the universe: for the first time, scientists were able to directly observe the dark part of the universe that does not emit light but that does have a lot of mass and energy, which includes black holes, and even information about the Big Bang.

This success story underscores the importance of basic science to scientific advancement and innovation – without Einstein’s thought experiments and predictions, this step forward in our understanding of the universe could have gone unnoticed because scientists would not have known where to look.



LIGO uses pure glass mirrors to detect gravitational waves
Image Courtesy Caltech/MIT/LIGO Laboratory

Scientists from all over the world collaborated on this project at the Laser Interferometer Gravitational-Wave Observatory (LIGO), led by Caltech and MIT. Collaborators included scientists at Canadian Institute for Theoretical Astrophysics at the University of Toronto and the Perimeter Institute at the University of Waterloo.

Based on the observed signals, the cataclysmic event causing the waves involved a pair of black holes around 29-36 times the mass of our sun, which circled one another until they ultimately collided around 1.3 billion years ago. On collision, about 3 times the mass of the sun was converted into a burst of energy in the form of gravitational waves within a fraction of a second. The peak power output of the event would have been around 50 times that of the entire visible universe.

The gravitational waves were detected on Sept 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin LIGO detectors, separated by 3000 km to rule out any local phenomena that might shake the instruments. One detector is located in Livingston, Louisiana, and the other in Hanford, Washington. The signal was recorded in Livingston 7 milliseconds before it was detected in Hanford, narrowing the location of the source to the Southern Hemisphere.


Gravitational waves detected at twin LIGO facilities, resulting in matching disturbances, separated by 7 milliseconds
Image Courtesy Caltech/MIT/LIGO Laboratory


Approximate source of the observed gravitational wave, based on the time separation of the two observed signals
Image Courtesy Caltech/MIT/LIGO Laboratory

The video below from the New York Times describes the impact of this observation, and shows how the LIGO experiment works.

Observation of gravitational waves confirms Einstein’s Theory of General Relativity, allows scientists to listen to signals from events that do not produce light
Video courtesy of The New York Times

Briefly, LIGO uses an L-shaped design, with mirrors placed at each end of the L, in hopes of detecting gravitational waves. Each arm of the L is 4 km long, and to keep the mirrors as still as possible, the system is isolated from the vibrations of heat, sound, and mechanical movement, and operated in a near vacuum.

LIGO uses a laser light source that is split into two halves, each traveling down one arm of the L. At the ends of the L, the light is reflected off the mirrors to travel back to a detector to recombine. Under normal operation, the two arms are exactly the same length, and each wave perfectly cancels out the other, producing zero light.

As a gravitational wave passes through spacetime, it compresses space in one direction, and stretches it in the perpendicular direction. If you picture the arms of the L, one arm lengthens as the other shortens, and then the reverse, oscillating until the wave passes through. This push and pull results in differences in distance traveled, producing a pulsing light signal at the detector.

A true event would pass through both of the twin detectors in close succession.

You can think of it like a stone causing ripples on the surface of a lake where insects are floating. As the waves pass over, some of the insects might be pushed together, and others might be pulled apart. By studying the effects of the wave, you can start to tease apart information about the source of the disturbance, such as its size and the impact location.

The detected signal has been described as a “chirp” – but on reaching the Earth was as faint as a whisper, moving the pair of mirrors only four one-thousandths of the diameter of a proton.


Twin L-shaped LIGO facilities in Livingston, Louisiana (left) and Hanford, Washington (right) are separated by 3000 km to rule out local causes of vibration
Image Courtesy Caltech/MIT/LIGO Laboratory

Not content to stop here, scientists have already launched an even bigger gravitational wave observatory into space, increasing sensitivity by increasing the arm length of the interferometer. Dubbed the Evolved Laser Interferometer Space Antenna (eLISA), it will be the largest man-made structure ever, with three satellites arranged in a triangle, and separated by equal arm lengths of 1 mil­lion km. Operations are set to begin in March 2016.

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Karyn Ho is a science animator and engineer who thrives at the interface between science, engineering, medicine, and art. She earned her MScBMC (biomedical communications) and PhD (chemical engineering and biomedical engineering) at the University of Toronto. Karyn is passionate about using cutting edge discoveries to create dynamic stories as a way of supporting innovation, collaboration, education, and informed decision making. By translating knowledge into narratives, her vision is to captivate people, spark their curiosity, and motivate them to share what they learned.