The Milky Way is a far from unique galaxy, but when paired with its close companions – dwarf galaxies, the Magellanic Clouds – it is very rare. However, now astronomers have found the first group of galaxies that appear to be just like it.
Using the most detailed map of the Universe yet, the Galaxy and Mass Assembly survey (GAMA), astronomer Dr Aaron Robotham and colleagues searched for groups of galaxies similar to our own.
Robotham, who is jointly from the University of Western Australia node of the International Centre for Radio Astronomy Research (ICAR) and the University of St Andrews in Scotland said: “We’ve never found another galaxy system like the Milky Way before, which is not surprising considering how hard they are to spot! It’s only recently become possible to do the type of analysis that lets us find similar groups.”
Our spiral galaxy is orbited by close neighbours, the Large and Small Magellanic Clouds, which can be clearly seen in the southern hemisphere night sky. Many galaxies are circled by smaller ones, but few are orbited by two that are as large as the Magellanic Clouds.
Simulations of how galaxies form tend not to produce many examples similar to the Milky Way and its neighbours, suggesting it is fairly unique. Astronomers have only just been able to tell how rare it is, with the discovery of just two exact matches in the hundreds of thousands of galaxies surveyed.
Robotham’s team found 3% of galaxies that were similar to the Milky Way had companion galaxies like the Magellanic Clouds, and 14 galaxies systems in total that are similar to ours.
The team concluded that while neighbouring galaxies like the Magellanic Clouds are rare, they are usually found near a galaxy like the Milky Way. However, Robotham reckons that these large companion galaxies don’t last long – cosmologically speaking. “They will only be around for a few billion more years,” he stated.
Dr Robotham presented the findings at the International Astronomical Union General Assembly in Bejing. He and his team have been awarded further time on telescopes in New South Wales and Chile to study these ‘twin’ systems now that they’ve been discovered.