The International Center for Radio Astronomy Research (ICRAR) reports that our own Milky Way galaxy has a twin. This new finding was presented today at the International Astronomical Union General Assembly in Beijing.
Taken alone, the Milky Way is not an unusual galaxy and there are likely many others like it. But the Milky Way has two companions known as the Magellanic Clouds, irregular dwarf galaxies that orbit the Milky Way. This particular arrangement of galaxies is quite irregular. Some believed that it was totally unique. But a recent survey of our local universe, or the universe in the area of the Milky Way, has identified two other groups of galaxies that appear nearly identical to our own.
Dr. Aaron Robotham of the University of Western Australia node of the International Centre for Radio Astronomy Research and the University of St Andrews in Scotland, who worked with the survey data, says: “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. Everything had to come together at once: we needed telescopes good enough to detect not just galaxies but their faint companions, we needed to look at large sections of the sky, and most of all we needed to make sure no galaxies were missed in the survey.”
The survey examined hundreds of thousands of different galaxies and found only two galaxies similar to the Milky Way that had companion galaxies similar to the Magellanic Clouds. While it is not unusual for galaxies to have companions, it is unusual for them to have multiple companions that are as large as the Magellanic Clouds. The Magellanic Clouds are so large and bright that they can be seen clearly from the southern hemisphere at night without sophisticated imaging equipment. In fact, the first historical mention of the dwarf galaxies comes from the year 964 in the Book of Fixed Stars, a work by the Persian astronomer Al Sufi.
Though dwarf companion galaxies like the Magellanic Clouds are very rare, they do tend to accompany galaxies much like the Milky Way.
Dr. Robotham goes on to say: “The galaxy we live in is perfectly typical, but the nearby Magellanic Clouds are a rare, and possibly short-lived, occurrence. We should enjoy them whilst we can, they’ll only be around for a few billion more years.”