The Small Magellanic Cloud (SMC) – a dwarf galaxy orbiting near our own Milky Way – appears to be meeting a rather dramatic end.
That’s the conclusion of a new study published in The Astrophysical Journal Supplement Series, where astronomers tracked more than 7,000 massive stars in the SMC – each one over eight times the mass of our Sun.
These stellar heavyweights burn bright and fast, living short lives that offer clues not just about their own movements but also the turbulent gas clouds from which they’re born.
And what the researchers found was striking. This once-cordial cosmic neighbour is being rather rudely torn apart by the gravity of the Large Magellanic Cloud (LMC) – another nearby dwarf galaxy that’s slightly larger and apparently not above throwing its weight around.
“The SMC is an interacting galaxy, gravitationally bound to the LMC,” Satoya Nakano, the study’s first author, told BBC Science Focus. “The stars on the side of the SMC closer to the LMC are experiencing a stronger gravitational force and are moving towards the LMC, while the stars farther away experience a weaker pull.”
This gravitational tug-of-war – along with a possible nudge from our own Milky Way, which looms some 200,000 light-years away – is slowly pulling the SMC apart.
So, why does this matter?
For one, the team discovered that the SMC isn’t rotating the way astronomers had assumed. Spiral galaxies like our own typically rotate, with stars and gas processing around a central axis. But not all galaxies do – and the SMC, it turns out, might be one of them.
“The question of when rotational motion emerges in galaxies is a topic of great interest among researchers,” Nakano said.
“The SMC was considered to be a rotating galaxy, but in this study, we’ve shown it’s not actually rotating. If we’ve misinterpreted even nearby galaxies like the SMC, it suggests we need to be much more cautious when assessing the rotation of galaxies farther afield.”
And the SMC is very nearby by cosmic standards. At just 200,000 light-years away, it’s more than 10 times closer than Andromeda – the nearest large galaxy.
The lack of rotation doesn’t just change our understanding of the SMC’s structure – it could also throw off estimates of its mass.
“Because the SMC is not rotating, our past estimates of its mass could be wrong,” Prof Kengo Tachihara, another of the study’s authors, told BBC Science Focus.
“Estimates for the mass came previously from its presumed rotational motion. But if these are not reliable, then we need to revise our estimates. Without this, we cannot predict what lies in the future for the SMC.”
Nakano and Tachihara hope their observations will open the door for detailed simulations to model the galaxy’s fate. But for now, its future looks far from bright.
About our experts
Satoya Nakano is a PhD candidate in the Department of Physics, Graduate School of Science, Nagoya University, Japan.
Kengo Tachihara is an associate professor at the Graduate School of Science, Nagoya University, Japan. His research has been published in prestigious journals such as Publications of the Astronomical Society of Japan, The Astrophysical Journal and Astronomy & Astrophysics.
Read more: