The $30 million VISTA survey reveals a gravitational tug-of-war

New research using VISTA survey data reveals that the Small Magellanic Cloud is expanding due to tidal forces from the Large Magellanic Cloud, overturning previous assumptions that it behaves like a rotating disk.

The Magellanic Clouds, two prominent satellite galaxies of the Milky Way, are locked in a gravitational dance that is reshaping their structures.

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This discovery challenges long-held assumptions that the SMC behaves like a rotating disk, highlighting the dynamic and often violent nature of galactic interactions.

The study, led by Sreepriya Vijayasree of the Leibniz Institute for Astrophysics Potsdam, used data from the VISTA Survey of the Magellanic Clouds (VMC), which provides unprecedented accuracy in measuring stellar motions over a timespan of up to 11 years.

Tracking millions of stars in the SMC

By tracking millions of stars in the SMC, the team found clear evidence of tidal forces pulling the galaxy outward, a process driven by the LMC's gravitational influence.

These findings not only deepen our understanding of the Magellanic system but also shed light on how satellite galaxies evolve in the presence of more massive companions .

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The VMC survey, conducted with the VISTA telescope in Chile,observes in near-infrared wavelengths, allowing astronomers to peer through dust that obscures optical views.

This capability is crucial for studying the stellar populations of the Magellanic Clouds,which contain a mix of young and old stars.

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The team measured the proper motions of stars-their apparent movement across the sky-and subtracted the SMC's bulk motion to isolate residual velocities.

The resulting map revealed a clear pattern of expansion along the southeast-northwest axis, consistent with tidal stretching induced by the LMC.

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This marks the first time such expansion has been detected across all stellar populations in the SMC, including its central regions.

The precision of the measurements is three times better than previous studies, thanks to the extended 11-year baseline of the VMC data release 7.