As a spiral galaxy, the Milky Way is far from unique. But what makes our galaxy particularly special is its pairing with the Magellanic Clouds — two irregular dwarf galaxies that are orbiting around it. Astronomers have never been able to find anything quite like it — at least not until now.
A new paper published in the Monthly Notices of the Royal Astronomical Society reveals that we're not completely unique in this regard — and that there are at least two galaxies out there that look almost exactly just like ours.
The finding was made by Aaron Robotham, jointly from the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR) and the University of St. Andrews in Scotland. Robotham and his team searched for galaxies similar to the Milky Way-Magellanic Clouds pairing by analyzing the most detailed map of the local universe yet, the Galaxy and Mass Assembly survey (GAMA).
That the Milky Way Galaxy is rare is not a complete surprise to astronomers. Computer simulations have largely been unable to replicate the formation of a megascale structural pairing like ours. Predicting their rate of occurrence throughout the cosmos, therefore, has been impossible. In fact, based on a sample of one, it was quite conceivable that ours was the only system quite like it in the observable universe.
Robotham's discovery now shows that this isn't the case — but it's clear that the configuration is still very rare. His research reveals that 11.9% of Milky Way-sized galaxies have one companion, and that 3.4% have two. But as it turns out, the Magellanic Clouds are quite large and close-by as far as companion dwarf galaxies are concerned. When looking for systems with similarly sized pairings, Robotham was only able to find two. His calculations show that only 0.4% of Milky Way-type galaxies have two galaxial clouds exactly like ours.
Moreover, Robotham has also concluded that companions like the Magellanic Clouds tend to hang around spiral galaxies similar to the Milky Way — but that they don't last long from a cosmological perspective. He suspects that they only last a few billion years and then disperse into the larger structure.
The entire paper can found at the Monthly Notices of the Royal Astronomical Society.
Top image courtesy Sci-News.