Nature has some pretty fancy tricks up her sleeves for us big brain apes. Oh! Don’t believe us? Engineers spend a lot of time, money, and resources to painstakingly craft the perfect lens for their telescopes; then all of a sudden, out somewhere void, the universe does one of it’s stunts by magnifying whatever that meets the eye. This natural phenomenon seems to magnify objects the power of sheer gravity within the universe. Dear friends, this is what’s known as gravitational lensing — and it’s helping scientists make some very big discoveries.
Related media: What Is Gravitational Lensing?
There’s A Curve In All Affaires
The theory of general relativity by German theoretical physicist Albert Einstein states that matter has the tendency to curve the fabric of spacetime, and as a result, any forms of light or energy that passes through that region gets distorted as the curve. Now, imagine the hypothetical scenario of a bowling ball resting on a trampoline — with the bowling ball acting as a massive object (like a star), and the trampoline acting as the fabric of spacetime.
What if you roll a marble as a traveling beam of light towards the bowling ball, the marble wouldn’t take a straight path on the fabric. Instead, it’ll follow the curve on the trampoline and bent towards the presence of the bowling ball. That’s exactly what light does around a massive object: the more massive an object, the deeper the curve on the trampoline, and the more the marble will bend around it.
This is exactly what happens when light rays pass through a magnifying glass or a telescope: light bends relative to the curve in the lens, which in turn creates an image of whatever is being perceived. In the case of a massive object in space, it could act as a magnifying glass for light around it. This cosmic lensing could play a huge role in aiding astronomers to see (detect) objects that are too faint and far away.
I’ll See You When You Curve There
Gravitational lensing isn’t perfect at resolving whatever is distant out there. In our trampoline analogy above, we could roll out several balls of varying sizes — like marbles, golf balls, and even beads. The odds are they won’t all take the same curve around the bowling ball; (and you guessed it) some would roll to the left, others to the right, some closer, and others farther away. It is the same way with how light travels.
This creates all sorts of distorted images — double images, arcs, rings, and whatever in the weird name of illusion; and it’s doesn’t really matter too much to astronomers. They have a clever way of detecting an object by observing it’s spectra — the light it emits in the electromagnetic (EM) spectrum — to determined what they’re seeing. However, the most important thing is the fact that this sort cosmic lensing in itself gives them much more information already.
Thence Cometh Dark Matter
Here’s the catch: the more a massive object, the more it’s gravity, thus the more it bends the light around it. This is what astronomers used in detecting stuff about distant objects — the degree of the lensing could be used to measure it mass, distance, and even luminosity of galaxies. But somewhere along the way, astronomers realized that all that information didn’t help them in crunching the numbers.
It seems that most distant galaxy clusters were bending too much light than what their actual mass would; and this discovery led to the hypothetical idea of “dark matter (and dark energy),” — the elusive substance that doesn’t emit or reflect light, but makes up 80 percent of the mass of the universe. Gravitational lensing is the only evidence that supports the existence of dark matter.
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Written by: Nana Kwadwo, Tue, Sep 10, 2019.