Science for All | What is gravitational lensing? 

The Hindu’s Science for All newsletters are carefully curated to help you understand the everyday happenings and wonders of the universe.

The Hindu’s Science for All newsletters are carefully curated to help you understand the everyday happenings and wonders of the universe.

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Gravity is a force to be reckoned with. This is somewhat surprising, as it is one of the weaker forces in nature, when you consider the strength of the electromagnetic force, which acts between charged magnetic particles such as the electron, or the strong nuclear force, which acts between components of the atomic nucleus, such as the protons and neutrons. Because it depends on the mass of the object, it can even mess with the fabric of space-time, and extremely massive objects can distort or distort the space-time around it.

Even light, despite being the fastest moving object in our universe, is diverted from its straight path when it comes close to a massive object, such as a very massive black hole. When we observe the light from a star passing near an intervening galaxy, it can again acquire a “lens” – a term implying that the galaxy’s gravity causes it to act as a lens and the light from the star distorts and magnifies. This can lead to different effects.

First, gravitational lensing can magnify the star’s image as we see it. Second, if the star we observe is exactly behind the intervening large galaxy, four images of the star have been produced around the image of the galaxy – a phenomenon known as Einstein cross. If it is slightly away from the line connecting us on Earth and the Milky Way, but beyond the Milky Way, the image we capture will be an arc of light.

Recently, scientists have imaged a star that is extremely distant, about 12.8 billion light-years away. Since a light-year is defined as the distance light travels in one year, this would mean we see this star as it existed 12.8 billion years ago — just 0.9 billion years after the Big Bang. This is very exciting because if confirmed, it would reveal to us the composition and nature of a class of stars that formed so early in the universe.

Scientists wouldn’t have been able to see this star were it not for its light to have actually passed through a ripple of space-time created by a galaxy that intervened. This accidental positioning of the star is what, thanks to gravitational lensing, made it possible for scientists to observe it.

Gravitational lenses are essential in discovering many celestial bodies today.

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