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Gemini South Observatory images NGC 4753's spiral dust disk, the result of a galaxy merger

NGC 4753 was discovered in 1784 by astronomer William Herschel and has some fascinating features. In this image, the complex dust lanes of the galaxy are a spectacular sight. NGC 4753 is about 60 million light-years away in the constellation Virgo

In this image, the complex dust lanes of the galaxy are a spectacular sight. NGC 4753 is about 60 million light years away in the constellation Virgo. Photo by ESO's Gemini South Telescope in Chile
In this image, the complex dust lanes of the galaxy are a spectacular sight. NGC 4753 is about 60 million light-years away in the constellation Virgo. Gemini South Telescope photo

The Lens Galaxy NGC 4753, imaged by the Gemini South Telescope, is a truly impressive object. The prominent and complex network of dust lanes winding around its galactic nucleus defines its type as "unique" and is probably the result of a galactic merger with a nearby dwarf galaxy about 1.3 billion years ago.

An astonishing number of galaxies exist in the observable universe, between 100 billion and two trillion according to recent estimates. And like snowflakes, no two galaxies are exactly the same. But they can be divided into four general types, according to their visual appearance and physical properties: elliptical, lenticular, irregular, and spiral, with many subtypes in between. But galaxies are dynamic objects that evolve over time due to interaction with the environment, and a specific galaxy can belong to several types during its lifetime.

Such is NGC 4753, which astronomers think started out as a regular lens galaxy but became a more specific type of "unique" after merging with a nearby dwarf galaxy more than a billion years ago.

NGC 4753 was discovered in 1784 by astronomer William Herschel and has some fascinating features. In this image, the complex dust lanes of the galaxy are a spectacular sight. NGC 4753 is about 60 million light-years away in the constellation Virgo. It belongs to the galaxy group NGC 4753 in the Virgo Cloud 2 - a series of at least a hundred galaxy clusters and individual galaxies at the southern end of the Virgo supercluster.

NGC 4753's unique dust lanes, which appear to meander around the galactic nucleus, have long intrigued astronomers and are the irregular features that give it the "unique" classification. From Earth you see the galaxy almost straight across the rim, and it can look very mysterious. But in 1992 a group of astronomers led by Tom Steinman-Cameron published a detailed study of NGC 4753 in which they found that its complex shape was likely the result of a merger with a small companion galaxy.

"Galaxies that swallow other galaxies often look like a disaster," Steinman-Cameron said, "and this is a disaster galaxy."

The product of merging galaxies

A galaxy merger happens when two (or more) galaxies collide, and their material mixes and significantly changes the shape and behavior of each of the galaxies involved. In the case of NGC 4753, the once normal lens galaxy is thought to have merged with a nearby gas-rich dwarf galaxy about 1.3 billion years ago. The dwarf galaxy's gas, along with bursts of star formation caused by this galactic collision, injected large amounts of dust into the system. The spiraling inward motion of the galaxy due to gravity caused the accumulated dust to spread into a disk shape. And this is where the story gets interesting.

Steinman-Cameron and his team found that a phenomenon called differential tilting is responsible for NGC 4753's winding dust lanes. Tilting occurs when the axis of rotation of a spinning object changes direction, like a spinning top that wobbles as it loses momentum. And differential means that the drop rate changes according to the radius. In the case of an accretion disk of dust surrounding a galactic nucleus, the accretion rate is faster towards the center and slower near the edges. This fluctuating motion was caused by the angle at which NGC 4753 and its former dwarf companion collided and is the reason for the highly tortuous dust lanes we see wrapped around the galaxy's luminous nucleus today.

"For a long time no one knew how to interpret this unique galaxy," Steinman-Cameron said. "But after we started with the idea of ​​an adsorbent that was spread into a disk shape and then analyzed the three-dimensional geometry, the mystery was solved. It is very exciting to now see this very detailed picture of Gemini South after 30 years".

to the announcement of the American National Science Foundation

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