The Milky Way’s second closest neighbor galaxy – the Small Magellanic Cloud – behaves unusually. Because the stars of this dwarf galaxy do not orbit around its center, as is normal for galaxies. Instead, they move outward and diverge in a north-south direction. This tearing movement not only affects the outer regions of the dwarf galaxy, but also extends into its center, as astronomers have determined. What’s behind it?
The Large and Small Magellanic Clouds are the Milky Way’s closest neighbors: the two dwarf galaxies are only 160,000 and 200,000 light-years away. It therefore has a close, not always “peaceful” history with our home galaxy. The Milky Way has repeatedly “stolen” stars, gas and entire streams of stars from its two neighbors. The two Magellanic Clouds also influence each other.
The Small Magellanic Cloud is apparently particularly affected by this: as early as the beginning of 2025, astronomers discovered abnormalities when analyzing the movements of a good 7,400 massive stars in this dwarf galaxy: A large part of its stars do not orbit around the center of the Small Magellanic Cloud, but move apart to two sides. The direction of this divergence suggested that tidal forces from the neighboring Large Magellanic Cloud could be at work.
A closer look at the stellar dynamics of our neighbor
However, how far this disturbance goes and what this means for the structure of the Small Magellanic Cloud initially remained unclear. That’s why astronomers led by Sreepriya Vijayasree from the Leibniz Institute for Astrophysics in Potsdam (AIP) have now examined the stellar dynamics in the Small Magellanic Cloud in more detail. To do this, they analyzed data from the European Southern Observatory’s VISTA telescope on Paranal in Chile, which was obtained as part of the VMC survey.
“The VMC survey was designed to map the Magellanic Clouds in infrared light in unprecedented detail, allowing us to peer through the dust and study stellar populations over a wide age range,” explains project leader Maria-Rosa Cioni from AIP. “The latest publication of the VMC data extends the observation period to a total of 11 years, enabling much more precise measurements of stellar movements than previous studies.”
Disturbance into the inner regions
The analysis of this data revealed that the star motion in the Small Magellanic Cloud is more profoundly disturbed than initially assumed. According to this, the stars of the dwarf galaxy move apart in a north-south direction at an average of 17 kilometers per second. This means that if this movement continues, these stars will shift by several thousand light years within a few hundred million years – enough to significantly distort the structure of the galaxy, as Vijayasree and her colleagues explain.
The new analyzes show that this expansion is visible not only at the edge of the galaxy, but also deep in its central regions. Even inside the Small Magellanic Cloud, many stars do not orbit around their galactic center, but predominantly move radially outwards. This anomaly is particularly pronounced in the younger stars of the dwarf galaxy: “In the young stellar population, we find no evidence of rotational motion, not even in the central regions of the galaxy,” the team writes.
But the older red giants in this dwarf galaxy don’t just move in circles: astronomers detected a pronounced movement to the northwest. “This suggests that this population of stars is responding to an older interaction of the Small Magellanic Cloud more than two billion years ago, the imprint of which is preserved in these older stars,” report Vijayasree and her colleagues.
No more orderly rotation
According to astronomers, these results confirm that the Small Magellanic Cloud is subject to strong tidal forces – and that it therefore has a much more complex dynamic structure than previously thought. “Our study shows that the internal movements of the stars in the Small Magellanic Cloud are not dominated by orderly rotation, but by gravitational perturbations,” says Vijayasree. “These disturbances were caused by repeated encounters with the Large Magellanic Cloud over billions of years.”
The gravity of the more massive Large Magellanic Cloud therefore acts on its neighbor and gradually pulls it apart. These disruptive effects extend into the center of the smaller dwarf galaxy and largely prevent its normal rotation. “The results challenge the long-standing assumption that the Small Magellanic Cloud behaves like a rotating disk,” says Vijayasree.
Will the dwarf galaxy be destroyed?
But what does this mean for the future of the Small Magellanic Cloud? Will it one distant day be torn apart whole or swallowed by its larger neighbor? According to astronomers who studied the dwarf galaxy’s pull-apart in 2025, this is not out of the question: “The unexpected movement we discovered supports the idea that this galaxy is being gradually destroyed by the Large Magellanic Cloud,” said Kengo Tachihara of Nagoya University at the time.
However, it is uncertain when the Small Magellanic Cloud will suffer this fate and whether something will come along.
Source: Sreepriya Vijayasree (Leibniz Institute for Astrophysics Potsdam) et al., Astronomy & Astrophysics, 2026; doi: 10.1051/0004-6361/202659431