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Astrophysicists confirm the very first observation of gravitational waves, due to the merger of a binary pair of black holes
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Big Astro News: LIGO experiment detects gravitational waves

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Scott Sutherland
Meteorologist/Science Writer

Thursday, February 11, 2016, 12:26 PM - Today, astrophysicists from LIGO - the Laser Interferometer Gravitational-Wave Observatory - announced the first detection of gravitational waves, ripples in the fabric of spacetime caused by two massive black holes consuming each other.

Roughly a century ago, Albert Einstein changed our view of the universe when he introduced his General Theory of Relativity. Part of this was the realization that space and time were not separate parts of the universe, but were woven together into the same fabric - spacetime.

If we could actually see spacetime, it would appear as a giant sheet stretching throughout the universe, and all the matter in the universe - planets, stars, nebula, galaxies, dark matter - would be resting on top of it. Each of these objects, both separately and collectively, would press down on the sheet, causing depressions in the fabric, with more massive objects causing deeper depressions. What we experience as gravity - the force that "pulls" us towards the center of the Earth, and what keeps Earth and the other planets orbiting around the Sun - is a consequence of these depressions, which have come to be known as gravity wells.


The Sun and Earth (not to scale) causing gravity wells in the fabric of spacetime. Credit: LIGO

Along with this concept of the "fabric" of spacetime came the realization that as objects interact with spacetime, they can cause ripples in that fabric.

An excellent example of this is two massive objects orbiting closely around each other. Put a binary pair of neutron stars or black holes together, and these massive, compact, fast-moving objects would cause swirling distortions - ripples, if you will - in the fabric of spacetime as they revolved around each other.


Binary neutron stars form gravitational waves in the fabric of spacetime. Credit: NASA

These ripples, even from the largest of masses, would be extremely small. They are exaggerated in the simulation above, so that we can see them, but according to the LIGO scientists, the ripples that were detected by their laser interferometer were roughly a thousandth of the width of an atomic nucleus.

So, what happened, exactly, and what did this detection look like?

Over one billion light years away, two massive black holes - one 29 times the mass of our Sun and the other 36 times the mass of our Sun - were orbiting around each other. As the pair distorted spacetime around them, the ripples they set off spread throughout spacetime, carrying away energy, which caused the pair's orbit to slow. This locked the two into a death spiral which eventually ended with their merger, which caused an intense pulse of gravitational waves that travelled across the fabric of spacetime until they reached us here at Earth.

Although the merger happened roughly 1.3 billion years ago, those ripples arrived here at exactly 5:51 a.m. Eastern Daylight Time, on September 14, 2015, and as they swept through local spacetime, it caused the Earth to "jiggle" ever so slightly. The effect was so small that nobody on Earth would have been able to sense that anything had happened, but the detectors at the two LIGO facilities - one in Hanford, Washington, and the other in Livingston, Louisiana - picked it up. These detectors are so sensitive that they can measure the distance between our Sun and the nearest star - a span of over 40 trillion kilometres - with an accuracy down to the width of a human hair.

Why is this detection important?

So, what's the big deal here? Why is this announcement so important, and why has it caused so much excitement in the science community?

When Einstein first figured out that massive objects could cause these ripples in spacetime, he also concluded that they would be so tiny that there would be no way to detect them. One hundred years later, scientists have actually accomplished this, using ingenuity to overcome the limitations that Einstein had seen at the time. So, that - on its own - is a fairly exciting achievement.

More importantly, though, this detection further solidifies Einstein's theories, and it represents an advancement in our understanding of how the universe works.

Dr. Katherine J. Mack, a theoretical astrophysicist at Melbourne University, summed it up perfectly during an appearance on Australia's ABC News network:

Not just gravitational waves

Although the gravitational wave detection was the most important part of this announcement, one particular detail that might get lost if it was not mentioned is the discovery of this pair of binary black holes that set off the ripples that LIGO detected.

Up until now, the concept of binary black holes - two massive stellar remnants, left behind by the deaths of two immense stars - was really only in the realm of theory. Although the physics allowed for it, and even demanded their existence, astronomers still had not actually found any.

With the detection of their gravitational waves, which gave the researchers an idea of their mass, this confirms that binary pairs of black holes do actually exist.

Also, with this detection, a whole new branch of astronomy opens up. Gravitational waves carry information along with them - specifically about the events that caused them, but possibly about the spacetime they've travelled through since then. This is information that can't be obtained using any other kind of astronomy, so it gives us a whole new way of looking at the universe around us.

Sources: LIGO | Caltech

Watch Below: A simulation of a binary pair of black holes spiraling in to merge

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