The 10 strangest space structures discovered in 2021

The radio jellyfish is more than 1 million light-years wide.

(Image credit: Torrance Hodgson, ICRAR/Curtin University)

Orbiting more than 300 miles (480 kilometers) over Earth and separated by tens of millions of light-years from many of the interstellar objects it studies, the Hubble Space Telescope takes "working remotely" to a new extreme. Even as the world below grappled with another pandemic year, weird and wonderful space discoveries flooded in from above, with astronomers pulling back the curtain on monster black holes, invisible magnetic megastructures and a cosmic treasure trove of extraterrestrial planets.

As a reminder that the universe just gets stranger and stranger the farther you get from Earth, here are 10 of the most awesome, extreme and enigmatic space structures discovered in 2021.

They say that in space, no one can hear you wakka wakka wakka wakka. Tell that to the Pac-Man remnant, the gassy remains of an ancient supernova that have taken on a shape instantly recognizable to fans of the classic video game. The object, officially known as N 63A, is the product of a star that collapsed under its own weight in the not-too-distant Large Magellanic Cloud, located 163,000 light-years from the Milky Way. The resulting dispersal of superheated gas took on this shape by chance. But the bright "power pellets" sitting in Pac-Man's path are no coincidence; according to NASA researchers, the pellets are young stars, forged from the same gas cloud that bore Pac-Man's ill-fated progenitor star long, long ago. What a pity … Looks like that star ran out of extra lives.

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Galaxy clusters are the largest known structures in the universe bound together by gravity. They can contain thousands of galaxies, enormous clouds of hot gas and, sometimes, the glowing ghost of a jellyfish or two. In the galaxy cluster Abell 2877, located in the southern sky about 300 million light-years from Earth, astronomers have discovered one such jellyfish. Visible only in a narrow band of radio light, the cosmic jelly is more than 1 million light-years wide.

According to a study published March 17 in The Astrophysical Journal, no structure this large had ever been seen in such a narrow band of light. It may be that this cosmic jelly is actually a "radio phoenix" — a cosmic structure born from a high-energy explosion (like a black hole outburst), fades over millions of years as the structure expands and its electrons lose energy, and finally gets reenergized by another cosmic cataclysm (such as the collision of two galaxies). The result is an enormous structure that glows brightly in certain radio frequencies but dims rapidly in all others. It's a ghost, a jellyfish and a phoenix, all in one!

The star system, known as GW Orionis (or GW Ori) and located about 1,300 light-years from Earth, makes a tempting target for study; with three dusty, orange rings nested inside one another, the system literally looks like a giant bull's-eye in the sky. At the center of that bull's-eye are three stars — two locked in a tight binary orbit with each other, and a third swirling widely around the other two. In a paper published Sept. 17 in the journal Monthly Notices of the Royal Astronomical Society, researchers built on previous data to show that a wobbly misalignment in the star system's three rings is almost certainly caused by the presence of a large, Jupiter-size planet inside one of the rings. If confirmed by future research, this enormous world will become the first "circumtriple" planet, or planet orbiting three stars, ever detected in the universe — and will give Luke Skywalker's double-sunned home world Tatooine a real run for its money.

In 2019, researchers released the first (and, so far, only) photograph of a supermassive black hole, a gargantuan object about 6.5 billion times as massive as the sun and located some 55 million light-years from Earth in the galaxy Messier 87. This year, scientists took another look at the monster object using the Very Large Array observatory in New Mexico, focusing now on the enormous jet of matter and energy blasting out of the black hole's center. The team's analysis showed that the ginormous jet was hardly a straight shooter, but rather was contorted into a bizarre "double helix" structure by a corkscrew-shaped magnetic field that blasts out of the black hole and deep into space for nearly 3,300 light-years. This is the longest magnetic field ever detected in a galactic jet, the researchers said, and it provides a fresh view of one of the most common phenomena in the universe.

The center of the Milky Way functions like a giant particle accelerator, shooting beams of charged matter called cosmic rays out into the universe at near light speed. When researchers tried to map the density of cosmic rays near the galactic center in a Nov. 9 study in the journal Nature Communications, they discovered something puzzling: Even as cosmic rays gushed out of the galaxy's center en masse, a mysterious "barrier" was keeping a large portion of incoming cosmic rays from entering the center at all. The team could only speculate about the source of this cosmic ray barrier but suggested it could be a jumble of magnetic fields related to our galaxy's central black hole, the monstrous Sagittarius A*.

In an Oct. 26 study in the journal Astronomy & Astrophysics, scientists shared the discovery of a massive "shipyard" where galaxies are built, similar to the one our Milky Way grew up in. The giant structure, called a protocluster, contains more than 60 galaxies and is 11 billion light-years from Earth, placing it in a part of the universe that is only 3 billion years old. Protoclusters like this one form in regions of space where long threads of gas, called filaments, crisscross, providing a buffet of hydrogen for gravity to coalesce into stars and galaxies. The young galaxies coming together in this "shipyard" appear to be growing at a voracious, almost unrealistic speed, the researchers said. The finding suggests that ancient protoclusters were far more efficient at assembling the foundations of the modern universe than researchers ever imagined.

Two clouds of gas, both alike in dignity, appear side by side in the fair Milky Way. Known as "molecular clusters," these enormous provinces of star-forming gas stretch across the sky, seeming to form a bridge between the constellations Taurus and Perseus. It's a celestial tale of star-crossed love — and, according to recent research, it's also an enormous optical illusion.

New 3D maps of the region, courtesy of the European Space Agency's Gaia space observatory, show that these canoodling clouds are actually hundreds of light-years apart, separated by an enormous, empty orb entirely absent of gas, dust and stars. Dubbed the Perseus-Taurus Supershell, this newly detected chasm stretches about 500 light-years wide, according to a study published Sept. 22 in The Astrophysical Journal Letters, and was likely created by a catastrophic supernova millions of years ago. The good news is that the ancient explosion probably accelerated star formation on the edges of the supershell, the researchers wrote, giving this star-crossed tragedy a happy ending.

Earth, along with the rest of the solar system and some nearby stars, may be trapped inside a gigantic magnetic tunnel — and astronomers don't know why. A tube of vast magnetized tendrils, 1,000 light-years long and invisible to the naked eye, may encircle the solar system, astronomers proposed in a paper on the preprint database arXiv. The team's investigation into two of the brightest radio-emitting gas structures in our galactic neighborhood — the North Polar Spur and the Fan Region — revealed that the two structures might be linked, even though they are located on different sides of the sky. The glue that links these structures are long, twisting tendrils of charged particles and magnetic fields, resembling a "curving tunnel" that wraps around everything in between, including the solar system, the researchers said. It's unclear where this magnetic "tunnel" came from, but tendrils like these could be ubiquitous in the universe and possibly part of an all-encompassing web of crisscrossing magnetic-field lines, the authors suggested.

Black holes are messy eaters. When an unlucky star ventures too close to one of these voracious objects, the black hole's extreme gravity stretches the star into a long noodle shape in a process called "spaghettification." In May, researchers saw this untidy process happen directly for the first time, when a black hole located 750 million light-years from Earth and weighing 30 million times the mass of the sun trapped a passing star in its clutches. The disastrous encounter produced a bright flash of optical light, X-rays and radio waves that telescopes on Earth could clearly detect. But it also revealed an unusual pattern of absorption lines around the black hole's pole, showing a long strand of light wrapped many times around the black hole, like a ball of yarn. Because most absorption lines typically appear near the black hole's equator, the researchers concluded that they must be witnessing a stellar spaghettification in action. Now, how do they send an enormous napkin to another galaxy?

Finally, for an object much closer to home than any others described this year, how about a "mysterious hut" standing proudly on the far side of the moon? China's Yutu 2 rover spotted the cube-shaped anomaly on Oct. 29, with the object protruding just above an otherwise uniform horizon. Is it an alien obelisk, à la Stanley Kubrick's "2001: A Space Odyssey"? Or is it something far more boring, like one of the moon's many boulders? It will take Yutu two or three months to get a closer look — and, hopefully, a satisfying answer — according to the China National Space Administration. We'll be watching the sky optimistically until then.

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Brandon is the space / physics editor at Live Science. With more than 20 years of editorial experience, his writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. His interests include black holes, asteroids and comets, and the search for extraterrestrial life.

The 10 strangest space structures discovered in 2021

1. A star-munching "Pac Man" in the southern sky

2. A ghostly jellyfish, risen from the dead

3. The ultra-rare planet in Orion's nose

4. A helix-shaped black hole energy cannon

5. An invisible "barrier" shielding the galaxy's center

6. A massive "shipyard" of ancient galaxies

7. A 500-light-year-wide "cavity" in the Milky Way

8. The twisted magnetic "tunnel" that surrounds the solar system

9. The first view of a "spaghettified" star

10. A "mystery hut" on the far side of the moon