The Andromeda Galaxy

What is it?

Also known as Messier 31 (M31), the Andromeda Galaxy is the nearest regular galaxy to our own. It is between 2.2 and 2.9 million lys away from us. It can be found in the Andromeda constellation in the northern celestial hemisphere.
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History of Human Observation:

    • The Andromeda Galaxy is visible to the naked eye but was first recorded by Persian astronomer Abd-al-Rahman Al-Sufi in his Book of Fixed Stars, which he wrote in 964 AD. It is believed that it had already been observed by the early 10th century if not earlier.
    • In 1864, William Huggins used spectroscopy to determine that the “Great Andromeda Neubula” differed fromexternal image Pic_iroberts1.jpg gaseous nebulas because its spectra are more continuous.
    • It was first photographed in 1887 by Isaac Roberts, revealing its spiral shape for the first time.
    • In 1923, Edwin Hubble discovered that M31 is actually a galaxy itself, and external image m31cep.jpgis not within the Milky Way. He accomplished this by discovering Cepheid variables (stars that change predictably in brightness) within M31.
By studying the Andromeda Galaxy, astronomers are able to get a much better idea of the mechanics of galaxies that by studying our own galaxy. The Milky Way is largely obscured from our vision but we are able to see Andromeda rather clearly and in entirety. This allows us to observe many aspects of nebulas, supernova remnants, and galactic interactions.

General Information:
Andromeda, together with the Milky Way, the Triangulum Galaxy, and around 30 smaller galaxies, make up Local Cluster.
Surrounding M31 are a number of smaller companion systems, including: M32, M110, NGC 185, And I, And II, And III, And IV (possibly), And V, And VI, And VII, and And VIII.
The only supernova to have been seen in M31 was observed in 1885 by Ernst Hartwig.external image web~0.jpg The Andromeda Galaxy displays what appears to be a double nucleus. This could be because it actually has two centers as a result of accretion (the absorption of a smaller galaxy by a larger one) or it could be due to a dark cloud of dust obstructing part of a single nucleus.
It is believed that we are only able to see about ten percent of the mass in M31.
M31 is 140,000 ly wide and contains up to one trillion stars. The older stars in the galaxy are 13 billion years old.
Although it is over twice as large as the Milky Way, it has less mass, meaning that it is much less dense.
M31 is the only large spiral galaxy approaching the Milky Way. While most galaxies are growing farther and farther apart, Andromeda and the Milky Way are approaching each other at about 100 km/s. This is likely because they were formed near each other soon after the Big Bang and are now being pulled back together by gravity. It is likely that the two galaxies will collide sometime in the next two or three billion years.

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Recent Research
Recently, it has been discovered that Andromeda is probably still growing. It is able to take up more mass as it “feeds off” one of its neighbors – Triangulum.
There has also been research into how lopsided stellar disks enable super massive black holes to absorb gases at the center of galaxies. This may somehow explain the appearance of two nuclei in M31.

Personal Response

Overall, I think that the Andromeda Galaxy is a fascinating and promising subject. It enable us to better understand not only the universe, but also our own galaxy. After my research, I was left with some questions such as “What exactly are Cepheid variables and why were they an important discovery in M31?” and “What are stellar disks?” Overall, I was often confused by unfamiliar terms, especially in articles on current and recent research. One thing I would like to know is how the Andromeda Galaxy formed over time into what it is today. Also, what will be the eventual end for the Andromeda Galaxy?
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