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Gravitational Lensing

This is the second installment in my once-in-a-while newsletter, The Magical Universe. If you dig it, you can subscribe here!

Hi friends! It’s been a while and I’m very excited to present… 

Magical thing no. 2: Gravitational Lensing!

We all know that gravity affects objects. You drop a plate, it falls to the ground, it smashes, you tear up a little bit because it startled you and you’re still kind of a toddler in a small place deep inside. Bam, that’s gravity. But I didn’t know until recently that gravity affects light as well, in some super dramatic and amazing ways!

Ever wonder why a black hole is black? All the time, right? If you wondered so much why didn’t you look it up? It’s fine, I’ll just tell you: A black hole is “black” because it has so much mass that it’s gravity is strong enough to pull all the light it might emit, or any light that comes close enough to it, into itself. Or in fancier (and more accurate) science words:

The event horizon is the point outside the black hole where the gravitational attraction becomes so strong that the escape velocity (the velocity at which an object would have to go to escape the gravitational field) equals the speed of light.1

But the effects of gravity on light are not limited to inside an event horizon. Gravity can act as a lens, changing the shape or apparent position of an object. This happens when an object’s light interacts with gravity on its way to an observer. This is called gravitational lensing!

Have a look at the diagram above. We have an observer looking at an object (Object A), and another object (Object B) situated past Object A. The light from Object B is distorted by the gravity of Object A. The result, from the observer’s perspective, is 2 images of Object B, on either side of Object A. This can be observed in nature, like the Einstein Cross, for example: 

Believe it or not, this is an image of one galaxy (centre) and one quasar behind it. According to Wikipedia:

The quasar is located about 8 billion light years from Earth, while the lensing galaxy is located at a distance of 400 million light years.

This is pretty magical in itself, but gravitational lensing doesn’t just create multiple images of an object. Let me tell you about my favourite effect of gravitational lensing, the Einstein ring. Imagine holding a wine class on its side and looking through the base. The imagery behind the glass would distort itself in a ring shape around the stem. WELL GUESS WHAT, this happens in space too.

[ dramatic pause ]

This beauty is called the Cosmic Horseshoe, and is an image of two galaxies, the galaxy in the foreground distorting the light from the galaxy behind it. Einstein rings exist in amazing numbers, and feel awesome to look at. 

Here’s one last image for your enjoyment, a collection of awesome gravitationally lensed smears around Abell 2218, a super massive group of galaxies.  

Magical, right?

( images not from Wikipedia found here )

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