Space photo of the week: A cosmic ‘ghost’ peers through the universe’s past

This image from the Hubble Space Telescope reveals a distant galaxy that looks very different from our own Milky Way. Best seen from the Southern Hemisphere, NGC 6684 is a whopping 44 million light-years away and was spotted coincidentally during Hubble’s census of galaxies within 32.6 million light-years that it’s yet to image. It’s now about three-quarters of its way through this mammoth task.

Astronomers categorize galaxies based on their apparent shapes and physical features. NGC 6684’s hazy, ghostly shape is an example of a specific type of galaxy called a lenticular galaxy — meaning that when viewed side-on, it looks like a lens, according to NASA.

It differs from the Milky Way in how its stars are arranged. The Milky Way is a classic spiral galaxy — a rotating disk of spiral arms full of stars, with dark lanes of dust and empty space between them that orbit around a central bulge of stars. Lenticular galaxies like NGC 6684 still have a bulge of stars at their core but no spiral arms. Instead, there’s a disk of stars.

Lenticular galaxies contain older stars than spiral galaxies do, and astronomers think these galaxies could be aging spiral galaxies whose arms have faded, or spiral galaxies that have merged, according to NASA. Indeed, recent evidence suggests that the Milky Way may have been a lenticular galaxy billions of years ago, before a series of galactic collisions shaped its signature spiral arms. Other lenticular galaxies imaged by Hubble recently include NGC 1023, NGC 5283 and NGC 3489.

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