Thanks to LIGO upgrade, gravitational waves are discovered 100 years after Einstein first published theory of relativity

A team of astrophysicists from the University of Toronto (U of T) played an instrumental role in what is being called one of the most significant discoveries in decades: the direct detection of gravitational waves. Since 2010, the group has been working with scientists from 15 countries as a part of the Laser Interferometer Gravitational Wave Observatory (LIGO) collaboration. This recent breakthrough confirms the final prediction of Einstein's theory of relativity, one hundred years after it was first published.

What are gravitational waves?

According to Einstein's theory, gravity is the result of the curvature of space-time, and gravitational waves are ripples produced during cataclysmic events, such as the collision of massive objects like neutron stars or black holes. In this instance, LIGO has apparently detected the latter — the collision of two black holes roughly 1.3 billion light years from earth.

"It is absolutely stunning to see two ground-breaking discoveries at once," Associate Professor Harald Pfeiffer, told U of T News. "Not only were gravitational waves measured for the very first time passing through Earth, but these waves were caused by astronomical objects that have never been observed before."

How does the gravitational wave detector (LIGO) work?

Shoot a laser beam, split it in two at a right angle and send them down 4km long vacuum tubes, bouncing off mirrors 400 times before bringing them back together. If we get the length of those paths just right, the peaks of one of the beams will line up perfectly with the valleys of the other, completely cancelling each other out (this is called destructive interference). But if a gravitational wave passes by, the force of gravity should shrink one of the paths and lengthen the other. The result is that the beam won't cancel out perfectly, producing blips of signal. What's the catch? Gravitational waves from millions or billions of light years away will only shrink objects by a fraction of the length of a proton, meaning instruments need to be incredibly sensitive.

LIGO's first eight years are uneventful

In the previous eight years of operation (2002-2010), LIGO's attempts to directly detect gravitational waves were unsuccessful. At the time, LIGO's sensitivity met only minimum levels needed to detect cataclysmic events in nearby galaxies. And with such events taking place only about once every ten thousand years in a given galaxy, the team of LIGO scientists may have had to wait a long time. That's why LIGO went offline in 2010 to perform engineering upgrades.

LIGO detects gravitational waves four days before officially coming back online

Roughly five years later, on September 14, 2015, LIGO was in the process of bringing their observatory back online after upgrades that improved the sensitivity of their equipment by ten times, opening up 1000x greater volume of the universe. That's when LIGO received signals at both of their detectors within a fraction of a second apart. Rigorous validation, including work performed by the team at the University of Toronto, confirmed the signals were in fact gravitational waves produced by the collision of two massive black holes, measuring 29 and 36 times the size of our sun.

LIGO's detection of gravitational waves opens a new window through which we can observe the universe

Avery Broderick, an astrophysicist at the University of Waterloo and Perimeter Institute explains the significance of the detection of gravitational waves in an interview with Wired. "We've been studying the light side of the universe for the past 10,000 years," says Broderick. "LIGO is going to begin the process of studying the dark side." Essentially, the ability to detect and analyze gravitational waves provides a new way to analyze the universe.

The Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Breakthroughs that occur at Perimeter Institute, the Waterloo Institute for Nano Technology and the Institute of Quantum Computing (IQC) are leading to transformative commercialization opportunities in Ontario.


March 2, 2016

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