Eye of the Beholder

ESA/Webb, NASA & CSA, G. Mahler

One of the first verified predictions of general relativity is the gravitational deflection of starlight. The effect was first observed in 1919 during a total solar eclipse. Since stars appear as points of light, the effect is seen as an apparent shift in the position of stars near the eclipse. But the effect happens more generally. If a distant galaxy is obscured by a closer one, some of the distant light is gravitationally lensed around the closer galaxy, giving us a warped and distorted view of the faraway stars. This effect can also magnify the distant galaxy, making its light appear brighter, and we have used this effect to observe some of the most distant stars in the Universe.

But perhaps the most beautiful effect of gravitational lensing is what’s known as an Einstein Ring. This is where the distant galaxy is so perfectly centered behind the closer galaxy that its light is distorted into a circle of light. Einstein was aware of the effect but said in 1936 that “there is no hope of observing this phenomenon directly.” But as brilliant as Einstein was, he couldn’t imagine the power of modern telescopes.

We have now found dozens of Einstein rings, and one of the more beautiful examples was recently found by JWST, as seen in the image above. The close galaxy in the foreground is an elliptical galaxy that’s part of a large cluster known as SMACS J0028.2-7537. The more colorful galaxy warped around it is a spiral galaxy similar to the Milky Way. It is billions of years more distant, but perfectly aligned to create the almost perfect ring.

Of course, this image is only possible because of our vantage point. Astronomers in other galaxies wouldn’t catch such a wondrous image. Yet another astronomical example of how beauty is not only in the eye of the beholder, but also where that beholder is.