Categories: Astronomy

Astronomy Jargon 101: Gravitational Lens

In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll be seeing double with today’s topic: gravitational lens!

Einstein’s theory of general relativity tells us that matter and energy bend and warp the fabric of spacetime. Indeed, this bending and warping is exactly what we experience as the force of gravity, since the deformations in spacetime instruct matter how to move. This bending doesn’t just apply to matter, but also to light.

The means that gravity bends the path of light in a phenomenon known as gravitational lensing. This was one of the first predictions of the theory of relativity, and an expedition led by Sir Arthur Eddington to observe the bending of starlight during a total solar eclipse was the first test of Einstein’s famous theory.

There are three kinds of gravitational lenses, divided into how strong the effect is.

The first kind is called strong gravitational lensing. Astronomers see this kind of lensing around gigantic clusters of galaxies. When light from background galaxies passes through or near the cluster, that light bends, distorts, and even sometimes follows separate paths. The background galaxy then appears warped and distorted, and in some cases can appear in multiple locations around the cluster.

The second kind is much weaker, and hence is called weak gravitational lensing. This is caused by the light from distant galaxies passing through billions of light-years of cosmic structure on its way to our telescopes. This won’t visibly distort the images of galaxies, but gently tweak them. Astronomers use this mild distortion to estimate the amount of matter between us and the galaxy, helping them to build maps of the universe.

The last kind if called microlensing, and is by far the weakest, as its name suggests. When a small object passes between us and a star, the image of the star will briefly appear to flare and brighten, due to multiple beams of light from the star getting focused around the object. This technique allows astronomers to discover otherwise invisible things like black holes and rogue planets wandering the galaxy.

Paul M. Sutter

Astrophysicist, Author, Host |

Recent Posts

There’s Another, More Boring Explanation for those Dyson Sphere Candidate Stars

Dyson Spheres have been a tantalising digression in the hunt for alien intelligence. Just recently…

1 hour ago

Hundreds of Massive Stars Have Simply Disappeared

The lifecycle of a star is regularly articulated as formation taking place inside vast clouds…

2 hours ago

What’s Under This Hole on the Surface of Mars?

Human visitors to Mars need somewhere to shelter from the radiation, temperature swings, and dust…

2 hours ago

Sorry Spock, But “Vulcan” Isn’t a Planet After All

In 2018, astronomers detected an exoplanet around the star 40 Eridani. It's about 16 light-years…

5 hours ago

A Mini-Neptune in the Habitable Zone in a Binary Star System

Sometimes, it seems like habitable worlds can pop up almost anywhere in the universe. A…

6 hours ago

Astronomy Generates Mountains of Data. That’s Perfect for AI

Consumer-grade AI is finding its way into people's daily lives with its ability to generate…

9 hours ago