If you are in the Southern Hemisphere, you can see the Small Magellanic Cloud (SMC) with your naked eye. It’s a dwarf galaxy satellite of the Milky Way looking fuzzy in the sky. What you wouldn’t know from looking at it, is that it’s being torn apart by another satellite, also visible to the naked eye, the Large Magellanic Cloud (LMC).

In recent years, astronomers have been able to study the motion of the stars in the galaxy with outstanding precision. And there’s certainly something odd going on with the SMC. A different group suggested that it might be two galaxies instead of one, but this work argues that it is one galaxy in the process of becoming two.

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

The team looked at 7,000 massive stars in the galaxies. These are young stars that will only live for a few million years before going supernova. The team tracked their motion and that indicated that the galaxy was being torn.

“The stars in the SMC were moving in opposite directions on either side of the galaxy, as though they are being pulled apart,” Tachihara said. “Some of these stars are approaching the LMC, while others are moving away from it, suggesting the gravitational influence of the larger galaxy. This unexpected movement supports the hypothesis that the SMC is being disrupted by the LMC, leading to its gradual destruction.” 

The observations also suggest something else about the SMC. Galaxies tend to have a rotational motion. Massive stars are great for tracking that as they are young and often still influence and are influenced by the interstellar gas they formed from. The team found that there is no rotational motion in the stars, so the SMC is likely not rotating.

“If the SMC is indeed not rotating, previous estimates of its mass and its interaction history with the Milky Way and LMC might need to be revised,” co-lead author Satoya Nakano added. “This could potentially change our understanding of the history of the three-body interaction between the two Magellanic Clouds and the Milky Way.” 

Even though the SMC and LMC have been known since the birth of Humanity, there’s clearly a lot more to know about them. Astronomers have called on the international community to rename the Magellanic Clouds given the colonial atrocities perpetrated by Magellan.

A paper on this work is available in The Astrophysical Journal Supplement Series.