Milky Way Galaxy

Most people are familiar with the Milky Way, as it is the galaxy that hosts our very own Solar System. But, did you know that the Milky Way’s name comes from the fact that it looked similar to spilled milk to scholars in the past? Although this milk spill looks like one stretch of stars, the Milky Way actually has multiple arms that we can't see from Earth, due to reasons that will be explained in the blog.

Formation of the Milky Way

The Milky Way galaxy was originally formed during the cosmic Dark Ages, which was essentially “the period before stars and galaxies existed” (Eicher, 2019). Astronomers have never been able to observe the cosmic Dark Ages, but the Hubble Space Telescope allows us to see the early Milky Way, when it was just an infant. Based on the ripples of the cosmic background radiation (essentially the “echo” of the Big Bang), Astronomers can conjure an image of what the Milky Way looked like in its earlier stages.

Composition of the Milky Way

The Milky Way is classified to be a spiral galaxy, but more specifically, a barred spiral galaxy. Barred essentially means that the galactic center of a spiral galaxy looks like a “bar”, as shown in the image on the right. NASA’s Spitzer Space Telescope uses infrared light to discover and locate the areas of the Milky Way of which humans on Earth are not able to see with a naked eye. The arms that make up the spiral galaxy act as continents on the world map, making it easier to plot geography in the Milky Way. Our own Solar System is located in what is known as the “Orion Spur”, which is a small arm that lies in between the two larger arms, Sagittarius and Perseus. These arms orbit around a central black hole (located within the galactic center), which is known as “Sagittarius A*”. It’s a supermassive black hole that holds the entire galaxy together.

Size of the Milky Way

Due to the vast number of stars within the Milky Way and our own patch of the sky, it is hard to determine an exact number. Astronomers estimate the approximate number is about 100 billion stars within the Milky Way alone. The stars form the disk shape of the galaxy, and the diameter from one end to the other is about 100,000 lightyears (one lightyear is about 63241 AU, and 1 AU is the distance from the Earth to the Sun). The distance between each object in space is so wide that Astronomers have to use light years as units of measurement, instead of miles and kilometers- which can only measure distances on Earth in quantifiable numbers. Due to the large distance, it takes our Sun about 250 million years to orbit the galactic center. It would take a millenia for a human to be able to say a single Cosmic year (one Solar revolution) has passed!

Interstellar Medium

As we know, the Universe is astronomically enormous, and it happens to be filled with spaces that have nothing (a vacuum). What is this vacuum called, and what exactly is it?

The Interstellar Medium, commonly known as ISM, is essentially the empty space that exists between any celestial body. The Milky Way features a large ISM, especially since the whole galaxy is not only stars. About 99% of the ISM is composed of hydrogen gas, and the other 1% is dust from sources like comets, supernovae, etc. Within the Milky Way galaxy, the ISM makes up about 10% - 15% of the total distance between visible mass.

Collision With Andromeda?!

Astronomers and mathematicians have been able to peek into the future of the Milky Way by using mathematical modeling and various simulations that have been conducted using computer science. They predict that the Milky Way will merge with our cosmological neighbor, Andromeda. Astronomers are confident that Earth will survive, but our night sky will look nothing like it looks now (see image to the right for reference). Currently, the Andromeda galaxy is moving towards us at a speed of 250,000 miles per hour, which is actually really slow. Due to the vastness of space, traveling at fast rates on Earth is incomparable to fast rates in outer space. It is said that we will be caught in the largest galactic event in about 3.75 billion years.

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Thank you for reaching the end of this blog! We hope you learned something new about the Milky Way galaxy. Be sure to like, comment, and share! If you have any questions, feel free to wander into our little Universe by going to the Contact form located at the top right. Follow us on Instagram for more content! As always, keep gazing skywards.

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Bibliography

Anderson, B. (2019, December 28). AstroFan: The Interstellar Medium and Nebulae. Adler Planetarium.

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Hodge, P. W. (2022, May 26). Milky Way Galaxy | Size, Definition, & Facts. Encyclopedia Britannica.

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NASA. (2015, December). Imagine the Universe! Imagine the Universe! Retrieved July 10, 2022,

NASA. (2017, November 8). The Milky Way Galaxy. NASA Solar System Exploration. Retrieved July 10,

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Orwig, J. (2016, January 22). Outcome of Earth When Milky Way Collides With the Andromeda

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