They're calling it X17—and it might help solve a great mystery of nature. Scientists in Hungary say they've twice stumbled on the previously unknown particle while seeking evidence of a "fifth force" guiding our visible universe, CNN reports. "X17 could be a particle, which connects our visible world with the dark matter," says lead scientist Attila Krasznahorkay. The team first spotted evidence of X17 three years ago when observing electrons and positrons break off at unexpected angles from a decaying isotope of beryllium. Now, with some calling that a lab error, the scientists announced a similar find in the breakup of an excited helium atom. "This would be a no-brainer Nobel Prize" if accurate, says US physics professor Jonathan Feng. But what does it all mean?
Four known forces are running the visible universe—gravity, electromagnetism, and the strong and weak nuclear forces—but scientists have been seeking evidence of a "fifth force" to explain dark matter, which invisibly makes up most of the universe, and fulfill Albert Einstein's dream of building a "unified field theory" to explain all existence. Enter X17, whose unusual mass (17 megaelectronvolts) and blink-of-an-eye lifespan (less of a trillionth of a second) tell us it can't be a particle carrying the four established forces, per Science Alert. Which leaves ... what, exactly? Maybe a glimpse beyond the visible universe. And there's "no reason to stop at the fifth" force, adds Feng. "There could be a sixth, seventh, and eighth force." (Read more dark matter stories.)