Cosmic Turducken: Hoag's Object Is A Galaxy Within A Galaxy Within A Galaxy
Ring-shaped galaxies are exceedingly rare, making up a mere 0.1 percent of all known galaxies in the universe, but one of them is particularly peculiar: the cosmic ‘turducken’ that is Hoag’s object.
This galaxy within a galaxy within a galaxy, discovered by Arthur Hoag in 1950, is slightly larger than the Milky Way, measuring about 100,000 light-years across, according to Live Science. And sits about 600 million light-years away from Earth.
A recent Hubble Space Telescope image of the object reveals “a bright ring of billions of blue stars” forming “a perfect circle around a much smaller and denser sphere of reddish stars.”
Peering out between these two galaxies is a third ring galaxy, which Live Science noted is significantly farther away from us.
No one knows why Hoag’s object is the way it is. Hoag himself hypothesized that the object is actually a disk and the ring-shaped appearance is merely an illusion, caused by gravitational lensing — “an effect that occurs when extremely high-mass objects bend and magnify light”; however, we now know that this is not correct.
It’s possible that far in the past, another galaxy crashed into Hoag’s object, causing a split in the disk and warping its gravitational pull. But such an incident had occurred in the last 3 billion years, astronomers would see fallout from the crash, which they do not.
Live Science concludes, “Hoag's object remains a mystery wrapped in a riddle inside an enigma — you know, like a turducken.”