In the morning on 14-September, 2015 about 6 o’clock scientist witness something special that no human ever experienced. But it was not on earth. It was in space. That time two black holes colliding. Those black holes are thirty time massive than our sun. These two black holes had been orbiting to each others for about millions of years. But when they got close together they circled each other faster and faster than before. And then they collided and marched into a single black hole. This colliding also increases there mass. A fraction of second before their crash, they sent a vibrating across the universe at a speed of light.
But most interesting this is that in earth, billions of years later a very special detector called “Laser Interferometer Gravitational Wave Observatory“ or LIGO that picked that signal. This signal was lasted just for a fifth of a second. It was the LIGO`s first observation of gravitational wave.
The answer starts with the gravity and it is the force that pulls two individual objects together. It is the main case for everything in the observable universe. That’s means you are pulling on earth, the moon, the sun and every single star and they are also pulling on you. All of them, if any object having more mass than others then it will have more gravitational force. If the distance between two objects is high then gravitational force will be less.
If every existing mass has an effect on others mass in this universe and no matter how small it is, then changes in gravity can tell us about what those object are doing. Fluctuations in gravity coming from the universe are called gravitational waves. Gravitational waves move out from what caused them like ripples on a pond getting smaller as they move or travel from their center.
But what are they ripples on?
When Einstein devised his theory of relativity, he imagined gravity is a curve in a surface called space-time. A mass in space create a depression in space-time. Now if a ball rolling across the depression will curve like it’s being attracted by others mass. If the mass is bigger than depressing will be deeper and gravity will be stronger. When the mass making the depression moves that time it send out ripples in space-time. These are gravitational wave.
If human body is sensitive enough to feel or detect this wave we may feel like, we are being starched sideways while being compressed vertically. After that in next instant, we will feel like starched up and down while being compressed horizontally. Side wise then up and down and this back and forth will happen again and again as the gravitational wave passed right through you. But this happens in a very small scale that we cannot feel of it.
For this reason we built detector that feels for us to detect them. LIGO detector is now doing that for us. Once detector detects gravitational wave then scientists can extract information about the source of it. In a way, LIGO is a big gravitational wave radio. Radio wave traveling all around us but we cannot feel it and hear the music it’s carrying. It need right types of detector to extract music from it. LOGO detects the gravitational wave signal which scientists then study for data about the object that generated it.
Scientists can drive information like its mass and shape of its orbit. Even we can hear gravitational wave by playing their signal in a speaker. The black hole collision was just one example of what gravitational wave can tell us about the universe. Some others high energy astronomical events will leave gravitational echo too.
Every time we create a new tool to look after space, we discover something new that we never expected to see.