Astronomers have found the clearest evidence yet that the way galaxies rotate today was set in motion before galaxies even existed. A team led by Ming-Jie Sheng at Xiamen University has detected, with high statistical confidence, the imprint of primordial tidal forces on the spin of nearby galaxies — a decades-old prediction that had resisted direct confirmation. The work was published in Nature Astronomy.
From lopsided clumps to spinning galaxies
The idea being tested is tidal torque theory. A galaxy’s spin — its angular momentum — shapes its size, its form, and the internal motions of its stars and gas. Tidal torque theory holds that this spin was not generated by the galaxy itself but inherited from the earliest structures in the cosmos, when uneven clumps of gas and dark matter gravitationally tugged on one another.
The mechanism is intuitive. If a primordial clump were slightly elongated, the end nearer a massive neighbor would feel a stronger gravitational pull. That uneven tug would set the whole clump slowly rotating, and the galaxy that eventually condensed from it should carry that rotation forward. The theory has long been widely held, but turning it into a measurable prediction that matches real galaxies had proven stubbornly hard.
Winding the clock backward with ELUCID
To make the test work, Sheng’s team needed to know how matter was arranged in the early universe — not just how it looks now. They drew on the ELUCID project, which reconstructs the primordial distribution of matter by working backward from the positions of galaxies we can observe today. From that reconstruction, they predicted the pattern of spins that early tidal forces should have imparted, and then compared it against actual spin measurements from an instrument that maps the motion of gas and stars within individual galaxies across a large sample of the nearby universe.
The signal emerged most strongly in an unexpected place: the gas inside large, massive elliptical galaxies. There, the measured spin matched the predicted primordial pattern closely enough to rule out coincidence with very high confidence — the strongest demonstration to date that present-day galaxies retain a genuine imprint from cosmic infancy.
A new handle on the early universe
The result does not mean a galaxy’s rotation is entirely predetermined. Mergers and disordered growth scramble much of that primordial signal over billions of years, and the match, while significant, lives alongside a great deal of later-acquired motion. What the study does establish is that a continuous thread links the gravitational pushes and pulls of the infant universe to the galaxies we observe now.
That thread has value beyond galaxy formation. Because these primordial tidal forces are sensitive to the overall contents of the early universe, reading them through galaxy spins could open a new way to constrain properties that are otherwise almost impossible to measure directly — including subtle ingredients like cosmic neutrinos, which should leave their own faint mark on the same primordial tidal field.
© 2026 Homer Dávila Gutiérrez, FRAS — SKYCR.ORG. All rights reserved. Publication: Ming-Jie Sheng et al., A high-significance detection of primordial tidal torque imprints, Nature Astronomy (2026). DOI: 10.1038/s41550-026-02948-w
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 has detected, with high statistical confidence, the imprint of primordial tidal forces on the spin of nearby galaxies — the strongest confirmation yet of tidal torque theory. Using the ELUCID reconstruction of the early universe and IFU spin measurements, the correlation was strongest in the gas of massive elliptical galaxies. The result may open a new way to constrain cosmic ingredients like neutrinos. Published in Nature Astronomy.){kind=link}