For centuries it was believed that Andromeda is part of our Milky Way. It was only in the early 20th century when it was discovered that Andromeda was in fact, a separate galaxy. Scientists now know that it is the largest and brightest galaxy in the sky. It is also the most remote object visible to the naked eye. Andromeda is the most nearest galaxy to our Milky Way Galaxy. The Milky Way contains our planet earth and the rest of the solar system.
Andromeda is spiral shaped and one of the most massive galaxies in our part of the universe.
In moderately dark skies the galaxy is visible as an elongated, hazy patch, slightly brighter in the center, and fading away on the edges until it blends into the sky’s background.
Andromeda gets its name from the Andromeda Constellation. The galaxy is located near one of the edges of this constellation and hence it was named the Andromeda Galaxy. The word Andromeda is actually a name from Greek mythology. According to Greek legends, Andromeda was a Princess and the daughter of King Cepheus and his Queen Cassiopeia.
This Galaxy was first described in 964 by Abdul Rahman Sufi, a Muslim astronomer from Persia. Abdul Rahman mentioned the galaxy in his book called the “Book of Fixed Stars”. He described the Andromeda as a “nebulous smear”.
The Andromeda is also known as the Messier 31 or M31. The name comes from Charles Messier, a French astronomer who documented the Galaxy in his catalog called “Catalogue of Nebulae and Star Clusters”, published in 1771. The number 31 actually signifies that it was the 31st object on Messier’s list of astronomical objects.
Occasionally, it is also known as the NGC 224. This designation came from the New General Catalogue (NGC), a detailed list of astronomical objects documented by British astronomer, John Louis Emil Dreyer in 1888.
Up until the early 20th century, astronomers believed, Andromeda was a part of the Milky Way. This theory was proven wrong in 1920 when American astronomer Edwin Powell Hubble determined conclusively that Andromeda was not part of the Milky Way, and a separate galaxy far away from the Milky Way.
The first photograph of the galaxy was taken in 1887 by Issac Roberts, a Welsh astronomer
The total mass of the Andromeda is estimated to be about 1.8×1042kg making it one of the biggest galaxies in our local part of the universe.
Andromeda is gigantic. Scientists estimate the total number of stars in the galaxy to be around 1 trillion. This is about twice the number of stars estimated to be in the Milky Way Galaxy.
Andromeda Galaxy is at a distance of 2.2 million light years away from earth and hence the most remote object one can observe with the naked eye. This means that if we observe the Andromeda with our eye at any particular time, the bright light coming from the galaxy and reaching our eyes is actually 2.2 million years old. So, what we observe of Andromeda at any given moment with our eye actually happened or took place 2.2 million years ago. Amazing, isn’t it?
Scientists say that Andromeda was formed about 10 billion years ago from the collision and merger of smaller galaxies.
Andromeda Galaxy has a diameter of about 220,000 light-years, which means if someone travels at the speed of light, it would take 220,000 years for them to travel from one edge of the galaxy to another.
Astronomers believe that the Andromeda has at least 2 Spiral Arms. Spiral arms are areas in a galaxy with strong star formation and are called spiral because of the spiral shape they take on, due to the galaxy rotating on its own axis.
Andromeda is also enveloped in a massive halo of gas and it is estimated that the halo contains half the mass of the stars in the Andromeda itself. Halos are giant spheres encircling a galaxy. They may contain old stars, hot gases or even dark matter. Halos play an important part in star formation in galaxies, controlling the rate at which new stars form.
Andromeda’s halo is invisible and dark. It can’t be seen when observing the galaxy. Scientists were only able to discover the halo after observing bright objects in the galaxy behind the halo and observing changes in light patterns due to the halo. This halo is believed to contain gases and an abundance of elements heavier than hydrogen and helium.
Although, the galaxy is so huge and bright that it can be seen anytime of the year, the best time to get a good view is during autumn nights, when the sky is dark and clear.
The Andromeda Galaxy is approaching the Milky Way at a speed of 110km/s. Scientists believe that our Milky Way and the Andromeda will collide after 4 billion years. Imagine that!
Moreover, the Andromeda also has 14 dwarf or satellite galaxies. These galaxies are heavily influenced by interactions with their nearby parent galaxies and are constantly orbiting around them. M32 and M110 are Andromeda’s most prominent satellite galaxies.
The Andromeda is estimated to have at least 35 black-holes, one of which is at the core or nuclei of the Galaxy. This black-hole at the center has a mass of about 2×1038 kg, which is at least 100 million times more than the mass of our Sun.
At least 450-460 globular clusters orbit the Andromeda. Globular clusters are spherical clusters of mostly old stars that orbit their nearby larger galaxy. The spherical shape of these clusters is due to gravity binding them together. Typically, these are found in the outer regions of a galaxy, specifically the halo region.
Although it’s the largest galaxy in our part of the universe, the Andromeda Galaxy contains less dark matter than our Milky Way.
For now much of what we know about the Andromeda is still a mystery. Scientists still have a lot to discover about this galaxy which is so much similar to our Milky Way. Some say the Andromeda may even have planets like our Milky Way. And who knows, maybe these yet to be discovered planets support life like our Earth does. If this were true, maybe one day we’ll get to meet some friendly or not so friendly aliens who might actually even look like us and have the same DNA as humans.