Galaxies

Did you know that the Milky Way and the Andromeda Galaxy (the closest galaxy to ours) are predicted to be on a collision course, leading into the formation of what is often called “Milkomeda”? But what even are galaxies? According to NASA, galaxies are “cosmic islands” that are composed of “stars, gas, dust, and dark matter held together by [the] gravity” of a supermassive black hole (n.d.). In fact, our very own galaxy, the Milky Way, is composed of an estimated number of 100,000 stars (such as the Sun), with a supermassive black hole, named Sagittarius A*, at its center.

Formation of Galaxies

This is a difficult question to answer, to say the least, because the truth is, the scientific community still doesn't have an answer- though there are many theories. One such theory suggests that dense areas composed of hydrogen and helium formed into “small clouds swirling through space (HubbleSite, n.d.). These clouds collapse into stars due to gravity, which burn out; nonetheless, clouds continue to collapse and form larger clouds by spinning into each other, until rotating disks were formed. These rotating disks' gravity continued to pull more gas and dust into their orbits until stars started to form, which in turn formed a pattern of spiral arms. Space telescopes, such as the Hubble Space Telescope, are unable to observe the first generation of galaxies formed, but fortunately, the James Webb Telescope was designed to do exactly that. Once it reaches its orbital destination and is ready to collect data, scientists will be able to use it to not only detect the first generational galaxies, but perhaps even solve once and for all, how galaxies even came to be in the first place.

Types of Galaxies

Elliptical

One third of all the galaxies of the Universe are classified as elliptical galaxies. Composed of little gas and dust, these galaxies typically contain older stars and are not actively forming new ones. They appear to be "nearly circular to very elongated" (HubbleSite, n.d.). The rarest types of elliptical galaxies are known as Giant Ellipticals, which are about 300,000 light years in diameter, while the most common type of elliptical galaxies are known as Dwarf Ellipticals, which are about a few thousand light years in diameter. A theory suggests that Giant Ellipticals may have formed through the merging of smaller galaxies.

Spiral

Spiral galaxies make up a large portion of the galaxies in the Universe. They appear to be "flat, blue-white disks of stars, gas and dust with yellowish bulges in their centers" (HubbleSite, n.d.) and are actively forming new stars. The most common feature of a spiral galaxy is its spirals that start from its center, where a supermassive black hole is typically located. The Milky Way is the most common example of this type of galaxy, with the Sun located on the arm called Orion-Cugnus. Spiral galaxies can be further divided into two subdivisions: Normal Spirals and Barred Spirals. A barred spiral is a spiral galaxy who's arms start at the end of the bar instead of the bulge.

Irregular

Irregular galaxies contain very little dust. These types of galaxies are often found when astronomers study the galaxies that are located deeper into the Universe. It is important to note that the light observed from these galaxies has been produced billions of light years ago, and the light produced in present-day will take another billion light years to reach Earth. Because these galaxies are observed farther into the Universe, meaning farther in time, this most likely means that these types of galaxies were more prevalent earlier on in the Universe than they are now. This can be farther be backed with evidence found by the Hubble Deep Field Images, which suggest that the farther you go back into the Universe's history, the less developed they become.

But tangent aside, it is important to note that the three types of galaxies presented above are main categories used to classify galaxies, but this does not mean that there are not additional classifications, such as those used to describe merging galaxies. We encourage our audience to do further research, if they are interested in learning more!

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Bibliography

Administrator, N. A. S. A. C. (2015, April 8). Elliptical galaxy. NASA. Retrieved January 16, 2022, from

https://www.nasa.gov/multimedia/imagegallery/image_feature_299.html

Galaxies. HubbleSite.org. (n.d.). Retrieved January 16, 2022, from https://hubblesite.org/science/galaxies

Garner, R. (2017, October 6). Messier 101 (The pinwheel galaxy). NASA. Retrieved January 16, 2022, from

https://www.nasa.gov/feature/goddard/2017/messier-101-the-pinwheel-galaxy

Hille, K. (2015, April 23). NASA Hubble sees sparring antennae galaxies. NASA. Retrieved January 16, 2022,

from https://www.nasa.gov/content/goddard/nasa-hubble-sees-sparring-antennae-galaxies

Which spiral arm of the milky way holds our sun? EarthSky. (2022, January 14). Retrieved January 16, 2022,

from https://earthsky.org/astronomy-essentials/which-spiral-arm-of-the-milky-way-contains-our-sun/