There’s no better way to celebrate the 100th anniversary of Einstein’s proposal of relativity than successfully detecting gravitational waves. On February 11, 2016 the American Physical Society published a review letter stating that local Laser Interferometer Gravitational Wave Observatory (LIGO) detectors had done just that.
The wave came from two black holes merging into one. They call this a binary black hole merger and it is the first of its kind that we have come to observe. Essentially, two extremely dense objects are rotating around each other. Their immense gravitational pull brings these two black holes closer and closer together. Eventually the two dense masses merge into one.
As Einstein has famously proved, E=mc^2. The amount of energy present equals the mass, times the gravitational constant ( c ), squared. The more matter you have, the greater the potential energy. How much matter do we have? Well the black holes had similar mass, 36 and 29 times that of our sun.
What happens when all the sudden two extremely dense singularities with immense matter merge into one? The extra matter explodes into a low-frequency gravitational wave. This wave is something physics and mathematicians have predicted to exist for decades. The problem has been developing a laser sensitive enough to pick up the waves.
The gravitational waves were actually detected on September 14, 2015 at 5:51 EDT. To make it easy they named the signal GW150914. To ensure that the detection was real and not a false alarm, reports of the detection were not released to the public until months after. A false detection had occurred at LIGO in 2011. However, this time both of LIGO’s detectors in Hanford, Washington and Livingston, Louisiana picked up a gravitational wave signal. The frequency ranged from 35- 350 Hz in just under a half second. The black holes were 150 kilometers across and are estimated to have joined 1.3 billion years ago.
One may ask how any of this has any importance. Taken from the review letter itself:
“Our observations provide unique access to the properties of space-time in the strong-field, high velocity regime and confirm predictions of general relativity for the nonlinear dynamics of highly disturbed black holes.”
In layman’s terms it means that we have confirmed a long over-due prediction in physics: the presence of gravitational waves. It also means we have opened the door to so many incredible new opportunities in the sciences in understanding more how mass and gravity warp space-time and the outcome of two enormous amount of energies colliding together.
Another may ask how we can be sure that this detection is not another example of what happened to LIGO in 2011. Fortunately, this time extended measures were taken to ensure that the detection wasn’t a result from faulty machinery or an external factor. Thorough investigations were done on the lasers to guarantee that everything was operating correctly. As for external factors, there were no environmental occurrences at that time that would have disrupted the lasers.
Researchers at LIGO have already established what levels of outside magnetic, radio-frequency, acoustic, or vibrations excitations would have to occur to alert a detection in the laser. The probability of observing a noise as strong as GW150914 is incredibly small. The false alarm probability rate measures at 5 x 10^-6, or .000001 percent. If one had happened, a detector somewhere would have reported such an incident, but fortunately for physics this is not the case.
So yeah, we have detected gravitational waves for the first time and have observed our first binary black hole merger. I believe many would agree that this is one our biggest discoveries in the past century. Congratulations to Einstein for predicting gravitational waves. Happy 100th anniversary to his proposal of relativity, and job well done to all those working tirelessly on decoding our universe.
B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration). “Observation of Gravitational Waves from a Binary Black Hole Merger.” Phys. Rev. Lett. 116, 061102 – Published 11 February 2016
LIGO. “Gravitation waves detected 100 years after Einstein’s prediction.” News Release, Washington D.C./Cascina, Italy. 11 February 2016.