A team of astronomers including two UVic professors have made an amazing discovery that could change our understanding of how galaxies are formed. Their research looks at the behaviour of dwarf galaxies. A paper recently published in Nature journal entitled “A vast, thin plane of corotating dwarf galaxies orbiting the Andromeda galaxy” explains that about half of the dwarf galaxies orbiting Andromeda rotate in a pancake-like structure that is over a million light years in diameter, but only 30,000 light years thick. Before this discovery, astrophysicists expected that dwarf galaxies would orbit their larger galaxy in random patterns.
“This paper in particular is part of a big project that we started several years ago called the Pan-Andromeda Archaeological Survey,” said Julio Navarro, a UVic astrophysics professor and co-author of the paper. “It is an imaging survey to get a big picture [of] the Andromeda galaxy and all of its surroundings. But the area is so big that is takes hundreds and hundreds of telescopes and stitches them all together,” he says.
The observations took place at the Canada-France-Hawaii Telescope from 2008 to 2011 and were led by Alan McConnachie, another UVic professor and co-author of the paper. McConnachie is also the principal investigator of PAndAS and is on the National Research Council of the Herzberg Institute of Astrophysics in Saanich.
Dwarf galaxies are smaller than average galaxies. Dwarf galaxies can also orbit larger galaxies, and both the Milky Way and Andromeda have dwarf galaxies orbiting them.
“Andromeda is the nearest galaxy like us,” explains Navarro. “Basically, the Milky Way and Andromeda are the two big kids on the block of this whole volume in space where we live. We are the two biggest, but we are fairly far apart from each other.” He says although the discovery may change our understanding about the formation of large galaxies in the future, the discovery concerns the formation of the dwarf galaxies, not large galaxies. “I think we learn more about the surroundings of Andromeda and the environment in which Andromeda formed rather than Andromeda particularly,” said Navarro.
Navarro plans to continue to be involved in this project and suggests the next step to take in order to better understand the significance of the discovery is to complete more observations. “We want to find more satellites to make sure this finding is not just chance. We don’t think it is, but we always want to make sure.” He says the second step is to expand theoretical knowledge. This step involves running computer simulations to see under what conditions this structure can be found. Navarro has two UVic students currently running these simulations and hopes to find something soon. “My prediction is that we will figure out what it is. To me, I think it’s just the transient configuration of Andromeda swallowing all these galaxies at the same time, and that’s why we see this pattern. But it is still fairly uncanny.”
This uncanny pattern intrigues Navarro. “It’s a very unusual, unexpected formation,” said Navarro. “It suggests our thinking about how galaxies form is totally wrong.” For Navarro, this unexpected discovery is a good thing: “You only learn when you find something that is unexpected. If it’s expected, you already know it. You only learn when things go wrong, when predictions go wrong, when your models don’t work. That’s when you really learn.”
