The Nobel Prize in Physics 2017
The Laser Interferometer Gravitational-Wave Observatory and the first direct observation of gravitational waves
On September 14, 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the USA saw space vibrate for the very first time. Even though the signal was weak when it reached Earth, it is already promising a revolution in astrophysics. Gravitational waves are an entirely different way of tracking violent events in space and testing the limits of our knowledge.
The observed gravitational waves were formed in a cataclysmic collision between two black holes, more than a thousand million years ago. Albert Einstein was right again1. He had predicted gravitational waves by his general theory of relativity a century ago, but he had always been doubtful if they could ever be captured. Figure 1. Collision of two black holes leading to gravitational waves.
LIGO, the Laser Interferometer Gravitational-Wave Observatory, is a collaborative project with thousands of researchers interacting from more than twenty countries. The 2017 Nobel Laureates, pioneers Rainer Weiss and Kip S. Thorne, together with Barry C. Barish, brought the project to completion, having confirmed that more than four decades of effort has led to gravitational waves finally being observed.
What are Gravitational Waves?
Gravitational waves are ripples in the space-time where they arise when heavy objects accelerate and therefore generate disturbances in the gravitational fields2. These “wave distortions” move outward from the source at the speed of light and give effects that, in theory, are measurable when the waves reach Earth given ample sensitive detectors, such as LIGO. Although the effects are minuscule, even for cases of exploding stars or black holes spiraling closer to each other. In order to measure the waves, LIGO, the largest and most sensitive interferometer facility was built. The facility has been recording data since 2002, periodically undergoing upgrades to enhance its sensitivity. Its most recent upgrade came online at the end of summer 2015 and within mere weeks, on September 14 that year, LIGO registered the passage of a gravitational wave, which was significantly above the expected background noise levels. The event was named GW150914, and interpreted as a result of the merging of two black holes at a distance of about 400 Mpc from Earth. This extraordinary discovery pointed to a means of study the astrophysics of black holes in ways that were previously inaccessible.
Gravitational waves reveal the past
Figure 2. As the two black holes spiraled around each other, they emitted gravitational waves for many million years. They got closer and closer, before combining to form one black hole in a couple tenth of a second. The waves reached us, on Earth, 1.3 billion lightyears away,...