An artist's impression of gravitational waves generated by binary neutron stars.
R. Hurt/Caltech-JPL

Week in Geek - Ripples in spacetime edition

Can you think back to what you were doing on September 14, 2015 at around 4:50am EST? No? Okay, me neither. But I’m guessing every scientist involved in the Laser Interferometer Gravitational-Wave Observatory (LIGO) knows exactly where they were. That was the day and time of the first detection of gravitational waves.

The LIGO Laboratory operates two detector sites, one near Hanford in eastern Washington, and another near Livingston, Louisiana. This photo shows the Livingston detector site.

Gravitational waves are one of the many predictions of how the Universe behaves according to Einstein’s theory of general relativity. If you’re like me, you hear the words “theory of general relativity” and thoughts of complex equations and math beyond your wildest nightmares come to mind. But really, you can just think of it as Einstein’s idea of how gravity works. In high school physics, gravity is taught as an invisible attractive force between any two bodies of mass. General relativity actually “visualizes” this force as the deformation of spacetime around these bodies - the more massive the body, the larger the deformation. Gravity is just how bodies moving through spacetime are affected by this deformation (or warping).

Gravitational waves are a special type of warping that occurs when massive bodies are accelerated and a great example of that is two black holes merging - exactly what LIGO detected. As these two black holes orbited each other, their warping of spacetime caused them to orbit closer and closer together, faster and faster, in a runaway process. It’s the acceleration of this process and the eventual merging of them into a single more massive black hole that produced the gravitational wave signal detected by LIGO. The theoretical signal is shown below.

Abbot et al.

Just that story is enough to blow my socks off, but it gets even more mind-blowing when you learn the details of the actual signal. The waves took all of 1/5th of a second to pass through the LIGO detectors. And from that incredibly brief signal, scientist were able to extract the details of the system that caused it: 2 black holes, one 29 times more massive than our Sun and one 36 times more massive, spiraled into each other, merged, and formed a single black hole 62 the mass of our Sun, all at a distance of 1.3 billion light-years. How’s that for impressive? All that from ripples in spacetime that passed through our entire planet in less than a second and nudged the LIGO detectors (4 km apart already) away from each other less than the diameter of an atom. Yeah, that happened.

These plots show the signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington.
These plots show the signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington. The signals came from two merging black holes, each about 30 times the mass of our sun, lying 1.3 billion light-years away.
LIGO

For more details, visualizations, background, and impact on this amazing event I recommend the following:

Keep on geeking!

@Summer_Ash, In-house Astrophysicist

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Week in Geek - Ripples in spacetime edition