Gravitational lensing.
Look at the Webb telescope's first deep field image and you may notice
some galaxies that are stretched or banana shaped.
They're not actually shaped like this. So what makes them look like it?
Gravitational lensing.
Gravitational lensing occurs when a celestial object has such a massive
gravitational pull that it actually warps the time and space around it.
Imagine placing a ball on a piece of squishy foam.
The fabric of space --
the foam -- sinks down around the celestial object -- the ball.
And light that would otherwise travel in a straight line
follows the bend of the warped space, distorting and brightening light
from behind the celestial object -- a galaxy cluster in this case.
So why do we care?
Well, because with a natural
magnifying glass, we can see even more distant objects.
In Webb's first deep field here, the banana shaped
galaxies are actually much farther away than the galaxies in the central cluster.
We see them as stretched because their light is being warped
and magnified by the galaxy clusters in front of them.
And this lets us see much farther than we would otherwise be able to.