Science 3 min read

Hoag's Object: The Mysterious "Matryoshka Doll" Galaxy

Hoag's Object: A Nearly Perfect Ring Galaxy | Image Credit :  NASA, ESA, Hubble / Processing: Benoit Blanco

Hoag's Object: A Nearly Perfect Ring Galaxy | Image Credit : NASA, ESA, Hubble / Processing: Benoit Blanco

The Milky Way is a spiral galaxy characterized by its dense core surrounded by four spiraling arms of stars, gas, and dust.

But not all galaxies look alike. Some don’t have any spirals like ring galaxies that represent a rare type of galaxies in the universe.

One of the most known ring galaxies is Hoag’s object, which scientists aren’t quite sure as to how it formed.

A Galaxy Within a Galaxy… Within a Galaxy

Now thanks to the Hubble Space Telescope, a new picture provides new information and raises even more questions about this oddball galaxy.

Almost 70 years after its discovery, Hoag’s object remains a beautiful enigma. The most recent image taken by the Hubble telescope reveals an even weirder sight.

Geophysicist Benoit Blanco reprocessed the picture using an artificial intelligence algorithm, called Deep Prior, to suppress noise.

The sphere of stars at the core and the near-perfect round ring surrounding it appear more clearly. But in the dark area between the two structures, it’s possible to see yet another small ring galaxy.

Hoag’s Object Still Puzzling Astronomers

American astronomer Arthur Hoag discovered the galaxy that would bear his name in 1950. At first, he chalked its peculiar ring-like shape off as an optical illusion caused by gravitational lensing.

In the constellation of the Snake, some 600 million light-years away, lies Hoag’s object. With a size of around 100,000 light-years, it’s slightly larger than our home galaxy.

Hoag’s object looks like a cosmic bullseye with a yellow core of old stars encircled by a ring of younger bluish stars. Apparently, no spiral arms or anything visible holds the ring and the core together.

Astronomers can’t agree on the mechanism that might have caused Hoag’s galaxy to take this ring pattern.

One popular hypothesis is that the structure of Hoag’s object is the result of a cosmic collision between two galaxies.

Two to three billion years ago, Hoag’s object might have been a disk-shaped galaxy that collided with another galaxy.

A ring of stars and gases would then have formed around the core of one of the two galaxies depending on the gravitational interactions. However, astronomers have yet to find evidence supporting the occurrence of such major cosmic event.

One problem facing astronomers studying Hoag-type galaxies is their rarity. It’s estimated that less than 0.1% of all galaxies observed in the universe are ring-type galaxies. And of those cataloged, none compares to Hoag’s object when it comes to symmetry.

Read More: Scientists Take Extraordinary New Photos of the Milky Way Core

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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