In 1916, Albert Einstein first predicted the existence of gravitational waves through his theory of general relativity. These waves have been described as ripples in the space-time continuum and have been estimated to travel at the speed of light. It was later thought that certain violent events in the universe produced these ripples, for example, the collision of massive black holes or neutron stars. But for almost a century, we had no empirical evidence for these waves!
However, in September 2015, the highly sensitive Laser Interferometer Gravitational-Wave Observatory or LIGO in the United States made an unusual observation. The LIGO arms detected a weak signal that was as short as a fifth of a second. But, it was the âvoilaâ moment for astrophysicists! For the first time, they had traced and detected the presence of enigmatic gravitational waves.
Investigations revealed that the waves originated from the collision of the two massive black holes, which occurred about 1.3 billion light years away. This collision sent a vibration through the universe, and LIGO finally chose the ripple over a billion years later.
Have you ever wondered what makes gravitational waves so important? In this three-part article series, Dr Parameswaran Ajith answers some of the most worrying questions around these fundamental waves. He is an astrophysicist at the International Center for Theoretical Sciences (ICTS) in Bangalore and has done important work studying different aspects of gravitational wave astronomy.
Can you briefly explain what gravitational waves are?
We know that light is the electromagnetic wave, oscillations of electric and magnetic fields propagating extremely rapidly in space-time. Gravitational waves are oscillations in space-time itself.
Einstein’s general theory of relativity describes gravity as the curvature of space-time. Any massive object would curl space-time around it. The movement of such objects would produce oscillations that move at the speed of light. We can therefore consider gravitational waves as ripples in space-time.
What causes gravitational waves?
Any accelerated movement of any massive object will produce gravitational waves. However, most of the time, these waves are too weak to be detected by any technology imaginable. âStrongâ waves are only produced when extremely massive and compact (dense) objects move at very high speeds, for example two black holes colliding. These are very rare events, which occur in a galaxy once in just several million years.
Why is it essential to observe and understand these waves?
Among the many reasons to study gravitational waves, one important aspect is that these waves are as fundamental to physics as electromagnetic waves. Studying these waves is one of the most effective ways to understand gravity.
So far, we have learned most of the universe from astronomical observations of electromagnetic waves. The study of gravitational waves offers a whole new way of understanding the universe. Gravitational waves carry completely different information about the source.
For example, the light from a collapsing star (called a supernova) tells about what is happening at the level of the star’s expanding envelope. In contrast, gravitational waves can tell what is going on in the deep interior.
There are many astronomical phenomena, such as black hole collisions that emit no light but a lot of gravitational waves. In addition, gravitational waves are the only way to find out what happened in the universe within fractions of a second after the Big Bang. Astronomy using gravitational waves is a new window to the universe.
The interview is part of a series called Ask an astronomer. This gravitational wave interview series is published in three parts, published daily from July 12 From.
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