The origin of spin in spiral and elliptical galaxies has posed a long-standing puzzle for astronomers. One idea, known as tidal torque theory, proposes that galaxies’ spins are an imprinted record of the early universe, imparted by gravity long before galaxies first formed and still detectable in galaxies today.

Through new research published in Nature Astronomy, a team led by Ming-Jie Sheng at Xiamen University has put that idea to its toughest test yet.