A galaxy neighbouring ours is transforming in unexpected ways – and it could change our view of space, researchers say.
The Small Magellanic Cloud, or SMC, is one of the closest neighbours to our Milky Way galaxy, and is visible with the naked eye from Earth. as its name suggests, it is a small galaxy that is made up of large amounts of gas, and is gravitationally bound to our own galaxy alongside its own companion, the Large Magellanic Cloud or LMC.
All three of the galaxies, including our own, have been interacting for hundreds of millions of years. And the close relationship means that the SMC is one of the most studied galaxies, with astronomers taking detailed catalogues of its stars and gas, and understanding how it moves.
But that research has failed to answer a simple question about the unusual make-up of that galaxy. Its stars do not orbit around its middle, like usual, and astronomers have struggled to know why.
Now researchers think they might understand that unusual movement. The astronomers behind a new study suggest that it is the result of a crash between the SMC and the LMC.
The findings help explain that mystery but could also have consequences for our understanding of the rest of space, which has often used the SMC as a reference point for other galaxies.
"We are seeing a galaxy transforming in live action," said Himansh Rathore, a graduate student at the University of Arizona and the lead author of the paper. "The SMC gives us a unique, front-row view of something very transformative of a process that is critical to how galaxies evolve."
The researchers believe that roughly a few hundred years ago, the SMC crashed right through the LMC’s disk. The gravity from the larger neighbour changed the structure of the SMC, throwing its stars into a random motion, and its gas added pressure to that of the SMC so that its gas rotation was destroyed.
"Imagine sprinkling water droplets on your hand and moving it through the air – as the air rushes past, the droplets get blown off because of the pressure it exerts. Something similar happened to the SMC's gas as it punched through the LMC," said Rathore.
The research suggests that we might be wrong to use the SMC as a kind of baseline for other galaxies. "The SMC went through a catastrophic crash that injected a lot of energy into the system. It is not a 'normal' galaxy by any means," said Gurtina Besla, another researcher on the new paper.
The work is described in a new paper, ‘A Galactic Transformation—Understanding the SMC’s Structural and Kinematic Disequilibrium’, published in the The Astrophysical Journal.
