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A perfect cosmic circle captured by Webb shows a distant spiral galaxy bent around a closer elliptical one. This Einstein ring offers a glimpse into the warped nature of space and time. Credit: ESA/Webb, NASA & CSA, G. Mahler |
A stunning new image from the James Webb Space Telescope reveals a cosmic mirage known as an Einstein ring, where the light of a distant galaxy is warped into a perfect circle by the gravity of a closer one.
This rare alignment offers scientists a natural magnifying glass to study galaxies billions of light-years away. Thanks to Webb’s powerful instruments and support from Hubble, astronomers can peer into galaxy clusters and explore the evolution of the universe in unprecedented detail.
A Cosmic Optical Illusion: The Einstein Ring
This new Picture of the Month from the James Webb Space Telescope showcases a rare and striking cosmic phenomenon known as an Einstein ring. At first glance, the image might look like a single, oddly shaped galaxy—but it’s actually two galaxies separated by a vast distance. The closer galaxy sits at the center of the image, while the light from a more distant galaxy has been bent around it, forming a glowing ring.
Einstein rings occur due to a process called gravitational lensing, where light from a distant object is bent by the gravity of a massive object lying between it and the observer. This happens because spacetime, the very fabric of the universe, is curved by mass, and light follows those curves. While this bending is far too subtle to notice on everyday scales, it becomes dramatic on astronomical scales, such as when light from one galaxy passes near another galaxy or a cluster of galaxies.
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When we observe a distant galaxy with our telescope, its light may encounter another galaxy on its way to us. The foreground galaxy acts like a magnifying lens, bending the traveling light rays due to its gravity. This is called gravitational lensing. If the background galaxy, the lensing galaxy, and the telescope are perfectly aligned, the image appears as a ring – called an Einstein ring. Einstein rings were first theorized to exist by Einstein in his general theory of relativity. Credit: ESA |
Perfect Alignment Creates the Ring
When the background galaxy, the lensing galaxy, and the observer are almost perfectly aligned, this lensing effect creates a nearly complete circle of light: an Einstein ring. Depending on how precise the alignment is, the ring may appear full, as it does here, or only partially complete. These rare alignments act as natural magnifying lenses, allowing astronomers to study extremely distant and faint galaxies that would otherwise be invisible.
The lensing galaxy at the center of this Einstein ring is an elliptical galaxy, as can be seen from the galaxy’s bright core and smooth, featureless body. This galaxy belongs to a galaxy cluster named SMACSJ0028.2-7537. The lensed galaxy wrapped around the elliptical galaxy is a spiral galaxy. Even though its image has been warped as its light traveled around the galaxy in its path, individual star clusters and gas structures are clearly visible.
Mapping the Universe with Webb and Hubble
The data for this image were collected as part of the Strong Lensing and Cluster Evolution (SLICE) survey (program 5594), led by Guillaume Mahler of the University of Liège in Belgium. The project involves a team of international astronomers and uses the Webb Telescope’s Near-InfraRed Camera (NIRCam) to study how galaxy clusters have evolved over the past 8 billion years. In total, the survey is observing 182 galaxy clusters. This image also includes data from two instruments aboard the NASA/ESA Hubble Space Telescope: the Wide Field Camera 3 and the Advanced Camera for Surveys.