A little more than 1.3 billion years before 14 Sep 2015, a pair of 29 and 36 solar mass black holes orbited each other, slowly getting closer together. On that date, they merged into one black hole of 62 solar masses. Their merger radiated 3 solar masses of energy in a fraction of a second.
This animation from Simulating Extreme Spacetime SXS uses calculated effects from the equations of Einstein to simulate the view of the star field behind the black holes. Imagine you are close enough to watch their dance. Paths of starlight are altered by the masses of the black holes. It is also greatly slowed down. The black holes were actually moving a high fraction of the speed of light as they orbited just before merger.
Power is energy per second. The power of their merger exceeded the power of all the stars in the known universe by many times in the final hundredths of seconds. The fabric of space and time warped violently near the small but massive bodies and caused two LIGO detectors in the states of Washington and Louisiana to recorded the event almost simultaneously. LIGO stands for Laser Interferometer Gravitational-Wave Observatory.
Consider two ice skaters slowly revolving around each other at arms length. As they pull inward to decrease their radius of spin. That causes an increase in their frequency of spin due to conservation of angular momentum. The two black holes were doing the same over time. Their pull inward was caused by the attractive force of gravity. Unlike the skaters who remain as two close bodies, the black holes attracted each other so strongly that they merged into one body.
We see depicted in the next video from SXS the distortion of the fabric of space-time near the black holes. It is represented by depressions in the colored horizontal sheet. Notice the clock in the upper left. The final stages of this merger took place in a few tenths of a second. Bands of blue and purple gravitational waves radiate outward. After the merger, the black hole settles down but the gravitational waves continue to speed throughout space in all directions traveling at the speed of light.
Journey of a G-Wave
LIGO scientist David Reitze describes the journey of gravitational waves from their origin 1.3 billion years ago to now.
Sound of the Chirp
Scientists are especially excited by the audio signal one can hear from the LIGO detectors. The wave form caused by the orbiting black holes shows an increasing frequency and amplitude. At the 0.9 s time, the black holes orbited each other about 50 times per second. By 0.95 s, their orbit frequency rose to over 256 times per second. They merged at that moment and the sound stopped.
Two objects, each of diameter over 100 km and mass of about 30 Suns, orbited in a decreasing spiral to over 250 times per second and reached speeds of half the speed of light. This is the most energetic event measured since the Big Bang.
For the first time, we can hear the universe sending us information of this immensely powerful event. This clip is extracted from the original LIGO video. It has been slowed down to make easier to hear. Play it several times with the volume turned up.
Why So Important?
The first publication about gravitational waves was by Einstein in 1916. He expressed skepticism about their existence. Correspondence with others convinced him to re-evaluate his work. He published a set of equations which predicted the existence of the waves and that they would travel at the speed of light. There was no technology available to test the theory. The waving distances were much too small to detect. The announcement from LIGO comes 100 years after Einstein’s great idea.
A similar situation existed when Isaac Newton proposed his theory of Universal Gravitation in 1687. No technology existed which was sensitive enough to test the theory about attraction of masses toward each other. That technology came 110 years later in 1797-98 with the work of Henry Canvendish. He was able to confirm the correctness of Newton’s theory.
Improvements are planned for the LIGO machines. Other countries are joining in the search with their own detectors. A whole new field of astronomy is opening up to mankind with this achievement. It is as important as the invention of the telescope was to Galileo. That instrument opened the era of observational astronomy in ways no one could imagine at the time. LIGO and similar technologies will do the same. A bright future lies ahead.
Other Waves Explained
Waves are very important in our study of the world around us. They come in many types with certain features in common. This video by Henry Reich at Minute Physics explains gravitational waves in terms that should be familiar.