Astronomers have uncovered compelling evidence that one of the closest galaxies to the Milky Way is being gravitational torn apart by its larger companion.

Located approximately 200,000 light-years from Earth, the Small Magellanic Cloud (SMC) is a dwarf galaxy that, along with its neighboring Large Magellanic Cloud (LMC), orbits the Milky Way. While both galaxies are expected to eventually merge with the Milky Way in several billion years, a new study suggests that the SMC may face a more immediate and destructive fate.

The research, published April 10 in The Astrophysical Journal Supplement Series, reveals that the SMC is currently being pulled apart by the powerful gravitational forces exerted by the LMC. This conclusion is based on a detailed analysis of stellar motions within the SMC, conducted using data from the European Space Agency’s Gaia spacecraft.

“When we first got this result, we suspected that there might be an error in our method of analysis,” said co-author Kengo Tachihara, an astronomer at Nagoya University in Japan. “However, upon closer examination, the results are indisputable, and we were surprised.”

The SMC, which is part of the Local Group—a collection of about 30 nearby galaxies—is a relatively small, triangle-shaped system spanning just 7,000 light-years. It contains a few hundred million stars and completes an orbit around the LMC every 900 million years and around the Milky Way roughly every 1.5 billion years.

Despite its proximity, studying the SMC has posed challenges due to its modest size and the presence of obscuring interstellar dust and gas. However, thanks to data from Gaia’s third data release, researchers were able to track the movements of approximately 7,000 stars within the SMC.

The findings were striking. “The stars in the SMC were moving in opposite directions on either side of the galaxy, as though they are being pulled apart,” Tachihara explained. “Some of these stars are approaching the LMC, while others are moving away from it.”

This motion strongly suggests that the LMC’s gravitational pull is actively disrupting the structure of the SMC, gradually leading to its disintegration.

Further analysis revealed another anomaly: unlike in the Milky Way, the massive stars within the SMC are not rotating around a central axis. This unusual characteristic raises new questions about the SMC’s mass distribution and its past interactions with both the LMC and the Milky Way.

These insights are particularly valuable because of the SMC’s low metallicity and weak gravitational potential, qualities that are thought to mirror those of early galaxies in the young universe. Understanding the dynamics between the SMC and LMC could therefore provide a window into how galaxies evolve and interact over cosmic time.

“We are unable to get a ‘bird’s-eye view’ of the galaxy in which we live – as a result, the SMC and the LMC are the only galaxies in which we can observe the details of stellar motion,” said Tachihara. “This research is important because it allows us to study the process of star formation in connection with the motion of stars throughout the galaxy.”

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