Detecting ripples in a space-time was not an easy task, after-all it took 50 years of trial and error, and 25 years perfecting a set of instruments so sensitive that could finally show a distortion in space-time millions of light years away. The discovery of gravitational waves have stirred the whole world of astronomy and have posed all sort of fascinating questions for astronomers regarding binary black-hole systems. Perhaps in a way it has opened a new field of gravitational physics which will revolutionize our understanding of the universe during its infancy.
The game has just started and now that we know how to measure gravitational waves, experiments like LIGO can be further enhanced to have a broader view of events happening in and around the cosmos that we have never been able to see before, such as mergers of super-massive black holes in the early universe. But the utmost question is that how far back can we really go? What about the gravitational waves that occurred moments after the big bang, will LIGO’s discovery help us catch those?
Let us take a step back in time, we are now in an era where the masses involved in the events are large by stellar standards, they are dwarfed by the super-massive black holes that scientists believe are present at the center of almost every galaxy. Our very own galaxy, the Milky Way, hosts a hole of about 4 million sun masses, detected through the motions of stars orbiting it.
There are yet a lot to discover about these super-massive black holes. We presently understand them through the immense amounts of electromagnetic radiation, like visible light and X-rays, produced by gas cascades into them. We know the likeliness of the process of formation of black holes, where some gasses are too slow and near and others are too fast and away for the black holes to capture it. So, the intriguing questions are that how could they get so big?
The answer could be that collisions between these super-massive holes helped to grow them, particularly when they were comparatively young and had not yet gained much gas. However, a collision between two super-massive black holes can probably only happen if the two galaxies hosting them collide and merge too. But these event is impossible to happen in the current time as because galaxies are far away from each other. But what if we go back in time, a time when the universe was much younger and the galaxies were very nearer to each other.
So detecting gravitational waves from such collisions means going back in time and analyzing the most distant galaxies giving us direct traces about how important these events were in growing super-massive black holes early in their lives and in turn unraveling the truth of mystery about the universe.
But the collision of super-massive black-holes is not the end. The Big Bang, and particularly the eon of very rapid expansion dubbed inflation with enormous masses moving with almost light speed producing powerful gravitational waves are the goal we are looking forward to achieve. However, the most powerful signal comes from masses whose size is comparable to the scale of the universe itself. Since gravitational radiation has a typical wavelength larger than the masses emitting it, the “wavelength” of this radiation is itself similar to the entire size of the universe. So LIGO, or any other experiment that is smaller than the universe, will not be able to detect it.
The challenge is extremely difficult but a positive result could give evidence for the popular inflation theory, and offer explanations for several baffling features of the universe, such as why the distribution of matter is so standardized. Although finding such a signal is a colossal challenge, so was the direct detection of gravitational waves when first proposed half a century ago.