Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2025 February 26
A cluster of galaxies is shown with many galaxies
around the cluster center. A close look at this center
shows that it is encompassed by a narrow ring of light.
Please see the explanation for more detailed information.

Einstein Ring Surrounds Nearby Galaxy Center
Image Credit & Copyright: ESA, NASA, Euclid Consortium; Processing: J.-C. Cuillandre, G. Anselmi, T. Li

Explanation: Do you see the ring? If you look very closely at the center of the featured galaxy NGC 6505, a ring becomes evident. It is the gravity of NGC 6505, the nearby (z = 0.042) elliptical galaxy that you can easily see, that is magnifying and distorting the image of a distant galaxy into a complete circle. To create a complete Einstein ring there must be perfect alignment of the nearby galaxy's center and part of the background galaxy. Analysis of this ring and the multiple images of the background galaxy help to determine the mass and fraction of dark matter in NGC 6505's center, as well as uncover previously unseen details in the distorted galaxy. The featured image was captured by ESA's Earth-orbiting Euclid telescope in 2023 and released earlier this month.

Tomorrow's picture: open space


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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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