My astronomy blog - Part Two
Some facts about the Andromeda Galaxy
The Andromeda galaxy or Messier 31, M31, or NGC224 in the various catalogues, is a huge classic spiral galaxy in our local group. It is similar to our own galaxy, the Milky Way. However the two galaxies differ slightly in that our own galaxy is a barred spiral; that is it's nucleus has a bar extending it's full length. Andromeda has no such bar. It is larger than the Milky Way but the density of the two galaxies is about the same.
Below are some facts about the Andromeda Galaxy.
Andromeda or M31 is our nearest spiral galactic neighbour and the largest galaxy in the local group; a cluster of galaxies to which our own galaxy belongs.
The Andromeda galaxy is moving towards us. At the moment Andromeda is 2.5 million light years away from us. But as it is getting closer all the time, the gap between our two galaxies is closing. At present we are moving towards each other at about 140kilometres per second. There is a possibility that the two galaxies will merge within the next 5 billion years.
One remote but possible outcome of the merger is that because of the gravitational pull within the two galaxies, the sun could switch galaxies and become bound to the Andromeda system. Even if the two galaxies do not merge, there is still a small chance that the solar system could be ejected from the Milky Way and/or join the Andromeda galaxy.
The total mass, or density of the Andromeda Galaxy is roughly the same as our own galaxy even though Andromeda contains more stars. This is possibly on account of the Milky Way having more dark matter and dense interstellar matter. This interstellar matter which also consist of dust lanes and gas is a nursery for the formation of new stars, so at some point in time, our galaxy could be home to more stars than Andromeda.
Like our own galaxy, Andromeda has a large ring surrounding it. It is possible that it will be changing from a spiral galaxy to a ringed galaxy when the spiral arms have wound up tight around the nucleus. But another kind of ring happens when a smaller galaxy passes through the interstellar gas and dust of a larger galaxy. As it does it compresses the interstellar matter and leaves behind a trail in the form of a ring encircling the larger galaxy. This is the kind of ring we see in Andromeda today.
As the the Andromeda galaxy and our own galaxy are moving towards each other, it is predicted that the two galaxies will collide in about 3 billion years. It is unlikely that any stars themselves will collide during this galactic merger, as the spaces between individual stars in both galaxies are vast.
Andromeda has a double nucleus. The real reason for this is unknown, but at one time it was thought that billions of years ago a smaller galaxy strayed too close to Andromeda and was cannibalised by it. However this theory has been dropped as it is now no longer considered viable.
Andromeda is also home to a supermassive Black Hole in it's centre. This is in accordance with most spiral galaxies. Our own galaxy also houses a supermassive black hole.
A supernova has also been observed in Andromeda. This supernova, namely S Andromedae, was the first one to be observed outside our own galaxy. It was seen in 1885. A supernova occurs when a star, such as our sun, has exhausted all it's fuel and the result is a very large and violent explosion.
Finally the Andromeda galaxy is the only galaxy bright enough to be visible with the naked eye. It lies in the constellation of Andromeda near the Great Square of Pegasus. It appears very small as only the canter of the galaxy is visible to the naked eye. If the full diameter with spiral arms were visible it would be seen as seven times larger than the full moon.
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