Gravitational Tug-of-War Between Dwarf Galaxies Could Tear One Apart, Study Suggests

Astronomers have uncovered evidence that the Small Magellanic Cloud (SMC) is undergoing a “galaxy-wide tidal disruption” caused by the gravitational pull of its larger sibling, the Large Magellanic Cloud (LMC), according to a study published May 21 in *Astronomy & Astrophysics*. The findings challenge long-held assumptions about the SMC’s structure and highlight the dynamic interactions between dwarf galaxies orbiting the Milky Way.

What Causes the Tidal Disruption?

The study, led by Sreepriya Vijayasree of the Leibniz Institute for Astrophysics Potsdam, analyzed stellar movements in the SMC using data from the VISTA Survey of the Magellanic Clouds (VMC). Researchers found that nearly all stars in the SMC are moving outward at an average speed of 38,000 mph (61,000 km/h), aligned along a southeast-northwest axis. This motion, driven by the LMC’s gravitational influence, could eventually split the SMC in half, according to the team.

“The internal motions of stars in the SMC are dominated not by orderly rotation, but by gravitational disturbances caused by repeated encounters with the LMC over billions of years,” Vijayasree said in a statement. The LMC, located 160,000 light-years from Earth, exerts a stronger tidal force on the SMC—200,000 light-years away—than the Milky Way, despite the galaxy’s greater distance.

How Did Researchers Discover This?

The VMC survey, conducted using the VISTA telescope in Chile’s Atacama Desert, tracked stellar movements over 11 years. The dataset revealed the SMC’s stars are not rotating as previously thought but are instead expanding outward, a pattern consistent with tidal disruption. Maria-Rosa Cioni, a co-author of the study, called the results “outstanding” for ground-based observations, noting the survey’s precision in mapping the SMC’s internal kinematics.

The SMC and LMC are connected by the Magellanic Stream, a trail of gas and dust left from their gravitational interactions with the Milky Way. However, the new study emphasizes the LMC’s role in shaping the SMC’s fate, suggesting the dwarf galaxy’s irregular shape and lack of a central core may be consequences of this ongoing conflict.

Why Does This Matter for Astronomy?

This discovery raises questions about the structure and evolution of other Milky Way satellite galaxies. With at least 60 dwarf galaxies orbiting the Milky Way, the SMC’s fate could serve as a model for understanding similar interactions. The findings also underscore the importance of precise observational tools like the VMC, which will soon be enhanced by the One Thousand and One Magellanic Fields survey to further map stellar movements.

“Outstanding observations” like these are critical for refining theories about galaxy dynamics, according to experts. The SMC’s potential disintegration in 2.4 billion years—when both galaxies are expected to collide with the Milky Way—offers a rare glimpse into the violent processes that shape the universe.

Study: The VMC survey. LV. The coherent expansion of the SMC