The cosmos is full of puzzles, but some objects stand out as especially baffling—enigmas that have left astronomers scratching their heads for decades. Here are nine of the most mysterious objects in the known universe, each one sparking debate, wonder, and a sense that our understanding of reality is still in its infancy.

‘Oumuamua: Discovered in 2017, this cigar-shaped object zipped through our solar system on a trajectory unlike anything seen before. Was it an asteroid, a comet, or even something artificial? Its true origin and composition remain hotly debated.

The Red Rectangle Nebula: A stunning, symmetrical nebula unlike any other, the Red Rectangle glows with an eerie red hue and shows sharp, geometric shapes. How did it form such a precise structure in the chaos of space? Scientists still don’t have a clear answer.

Planet Nine: Astronomers are convinced there’s a massive, hidden planet far beyond Pluto—one that could explain the strange orbits of distant objects. But despite years of searching, Planet Nine has never been seen, and its existence is still unconfirmed.

Galaxy X: This so-called “dark galaxy” might lurk on the edge of our Milky Way, composed mostly of dark matter with few or no stars. Its presence is inferred from gravitational effects, but it has yet to be directly observed.

Elst-Pizarro: An object that blurs the lines between comet and asteroid, Elst-Pizarro sports both the orbit of an asteroid and the tail of a comet, confounding efforts to classify it neatly.

Tabby’s Star: Famous for its bizarre, unpredictable dimming, Tabby’s Star (also called Boyajian’s Star) has inspired wild theories ranging from swarms of comets to alien megastructures. No conventional explanation has fully accounted for its strange behavior.

These mysterious cosmic objects serve as reminders that the universe is not only stranger than we imagine it’s stranger than we can imagine. Each one is a cosmic riddle, waiting for the next breakthrough in science to bring us closer to an answer.

The cosmos is full of puzzles, but some objects stand out as especially baffling enigmas that have left astronomers scratching their heads for decades. Here are nine of the most mysterious objects in the known universe, each one sparking debate, wonder, and a sense that our understanding of reality is still in its infancy.