The naked eye can see a long way. In fact, on a clear autumn night in the northern hemisphere you will be able to see our nearest neighbouring galaxy, Andromeda, just 2.5 million light years away. Initially observed as a “small cloud” in 964 AD by Persian astronomer Abd al-Rahman al-Sufi, Andromeda was named M31 in 1764 by French astronomer Charles Messier.
Unlike the Milky Way, Andromeda possesses a dual core, which is believed to be the outcome of M31’s collision with the smaller elliptical galaxy M32 about 200 billion years ago. Its dual core has contributed to the sheer size of Andromeda, making its diameter twice that of the Milky Way. This collision process is believed to have occurred due to Andromeda’s “galactic cannibalism,” whereby the galaxy absorbs smaller galaxies.
Recent studies of the galactic cannibalism hypothesis have observed that Andromeda is not only indulging itself in dwarf galaxies, but has also set course for our own galaxy. Andromeda’s blue shift light has led astronomers to conclude from the Doppler Effect that the galaxy is moving towards our own, and could eventually collide with the Milky Way. Since Andromeda is 2.5 million light years away and its velocity is largely unknown, such a collision can only be speculated to involve multiple sideways swipe impacts, eventually merging M31 and the Milky Way into a larger elliptical galaxy. If such an event were to occur, the fate of our solar system would teeter between being ejected from the Milky Way entirely, remaining intact while encountering ever-increasing solar radiation, or having the sun exit the Milky Way by resettling in M31 during the initial impacts.
While Andromeda possesses a similar spiral shape to the Milky Way, one of its prized possessions is a giant outer ring consisting of many young and luminous blue stars. Astronomers believe this ring was created by the passage of dwarf galaxies through the center of Andromeda, which compressed the interstellar dust and gases to induce star formation. It is hypothesized that if M31 continues to devour small galaxies, the outer ring will increase in significance and change Andromeda from a spiral to a ring galaxy.
In the night sky, Andromeda Galaxy is the farthest object visible to the naked eye and is situated within its own constellation, aptly named Andromeda. In mythology, the constellation represents the Greek princess Andromeda, who was condemned to be sacrificed to a sea creature as payment for her mother’s conceited behavior — only to be saved by the Greek hero Perseus, who would later become her husband.
The galaxy can be best observed during the month of October, positioned to the north-west of the Square of Pegasus, which is similar in shape to the commonly known Ursa Major, yet it contains stronger right angles unlike the Big Dipper’s recognizable trapezoidal characteristics.
This week’s venture brought us 2.5 million light years away into the depths of Andromeda. Next time we will be waltzing through a mythical Greek hunter, stationed a little closer than our cannibalistic neighbor. Until then, the night sky remains a glance away, awaiting your adventures.
