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StarDateYour guide to the universe Author: Billy Henry
StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky. Language: en-us Genres: Astronomy, Education, Science Contact email: Get it Feed URL: Get it iTunes ID: Get it |
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Einstein Rings
Sunday, 7 December, 2025
A couple of years ago, a space telescope discovered something odd about NGC 6505. The galaxy is encircled by a ring. It isn’t part of the galaxy itself. Instead, it’s an image of a background galaxy – one that’s billions of light-years farther. Einstein Rings are named for Albert Einstein because they were predicted by his theory of gravity. The gravity of a foreground object acts as a lens – it bends and magnifies the light of a background object. On small scales, gravitational lenses have revealed everything from black holes to rogue planets. Galaxies are much bigger and heavier, so they produce more dramatic lenses. Many of them create bright arcs. But when the alignment is just right, they can create a full circle. NGC 6505 is a good example. The galaxy is about twice the diameter of the Milky Way, and several times its mass. It’s about 600 million light-years away. The background galaxy is four billion light-years farther. The lensing effect has allowed astronomers to measure the amount of dark matter in the center of NGC 6505, as well as details about its stars – discoveries made possible by its beautiful ring. NGC 6505 is enwrapped in the coils of Draco, the dragon. The galaxy is more than a third of the way up the northwestern sky at nightfall. It’s visible through a small telescope. But you need a big telescope and a long exposure to make out its ring. Script by Damond Benningfield
