Imma Perfetto
Cosmos science journalist
Large galaxies like our own, the Milky Way, are often orbited by smaller satellite galaxies that buzz about like bees around a hive.
The Small Magellanic Cloud (SMC) and its larger companion, the Large Magellanic Cloud (LMC), are some of our closest dwarf galaxies. They can even be seen with the naked eye in the southern hemisphere at night.
But new research from Japan suggests that the gravitational pull of the LMC might be tearing the smaller one apart.
“When we first got this result, we suspected that there might be an error in our method of analysis,” says Associate Professor Kengo Tachihara, who co-led the research at Nagoya University.
Tachihara and his team used data collected by the Gaia space telescope to track the movement of more than 7,000 massive stars in the SMC. These stars, which are more than 8 times the size of our Sun, typically only live for a few million years before exploding as supernovae.
“The stars in the SMC were moving in opposite directions on either side of the galaxy, as though they are being pulled apart,” says Tachihara.
“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.”
As these massive stars are so young, they are found in regions of space rich in a crucial component of star formation – hydrogen gas. Typically, they move together with the gas from which they formed, as they have not yet had time to decouple from its motion.
As we are unable to get a bird’s-eye view of the galaxy in which we live, Tachihara adds, the SMC and the LMC are the only galaxies in which we can observe the details of stellar motion.
But the study revealed an unexpected finding; the massive stars in the SMC do not follow a rotational pattern, which indicates that the interstellar gas itself also does not rotate.
“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,” says co-lead researcher, Satoya Nakano.
“This could potentially change our understanding of the history of the 3-body interaction between the Magellanic Clouds and the Milky Way.”
The research is published in a paper in The Astrophysical Journal Supplement Series.
