The Milky Way is far from alone in its corner of the Universe. Around our own galaxy, astronomers have detected roughly 60 smaller satellite galaxies, the biggest of them being the Large Magellanic Cloud with 1 percent of the mass of the Milky Way. Astronomers believe many more of these satellites exist, based on their latest model using dark matter.
As reported in a paper to be published in The Astrophysical Journal, the team used known satellites of the Milky Way to refine their model and make predictions about the intergalactic space. The model suggests that about 100 tiny galaxies are yet to be discovered around our galaxy.
"We know some things about dark matter very well – how much dark matter is there, how does it cluster – but all of these statements are qualified by saying, yes, that is how it behaves on scales larger than the size of our local group of galaxies," lead author Ethan Nadler, from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) and Stanford University, said in a statement. "And then the question is, does that work on the smallest scales we can measure?"
To answer this question, the team used a sophisticated galaxy formation simulation. The model is flexible to account for the many things we don’t know about dark matter. So far, what we do know is that this substance (if it really exists) appears to only interact with gravity, outweighs ordinary matter five-to-one, and keeps galaxies and galaxy clusters in shape. Using the simulation, the team looked for all the possible virtual universes where they could form the Milky Way’s companions as we see them today.
The key parameter in the simulation was the Large Magellanic Cloud. Last year, astronomers discovered that the Milky Way stole six satellite galaxies that used to belong to the Large Magellanic Cloud. This time around, the team included in the simulation the possibility where that particular factor came into play. The scenario provided insight into the past of the system, suggesting that the Large Magellanic Cloud had a close interaction with the Milky Way in the last 2 billion years, and provided the researchers with an idea of how many satellites are still yet to be discovered.
It's possible that once the work on the next-generation Vera C. Rubin Observatory is complete, it could be used to find the undetected satellites of the Milky Way.