Galactic Evolution

For 13.7 billion years, the Universe has been evolving, shaping the intricate galactic formations we observe today. From the ancient explosion of the big bang to the striking spirals and the giant ellipticals scattered across the cosmos, the journey of galactic evolution is the result of cosmic forces, stellar births and deaths, and the mysterious influence of dark matter. Understanding how galaxies form, grow, and transform can reveal the eons worth of history regarding the Universe. In this blog, we will explore the fascinating life cycle of galaxies, from their chaotic beginnings to their mature, prospering forms.

Galactic Classifications

Before we begin diving into the theories of how galaxies actually evolve, we must take a look at how different galaxies have been categorized. In 1926, an American astronomer by the name of Edwin Hubble would publish his classification scheme for galaxies.

The above tuning fork diagram displays the different galaxy formations and their unique characteristics, starting with elliptical galaxies. Elliptical galaxies exhibit smooth surfaces, featureless light distribution, appearing as ellipses in photos. Also, stars that orbit in elliptical galaxies tend to move in an unorderly fashion compared to that of a spiral galaxy. Lenticular galaxies as show in the diagram, located in the intersection (“S0”) between the spirals and elliptical galaxies are considered to be a transitory stage between ellipticals and spirals, connecting these two types. Their characteristics include a bright central bulge encased by a disk-like formation. Spiral galaxies present themselves in two different categories, normal spirals appear as flattened disks with the inclusion of stars which go to form the distinct spiral structure. Similarly, given the distinct shape, arms are observed to be tightly wound and a central point that consists of a high concentration of stars. Barred spirals on the other hand contain a bright linear feature known as a bar that spans the nucleus with the arms unravelling from the ends of the bar. Furthermore, irregular galaxies although not pictured in the diagram exist without a real structure. Astronomers believe that the unique distorted features of these galaxies are the result of gravitational forces from nearby galaxies.

 

Theories of Galactic Evolution

The evolution of galaxies is a complex and dynamic process, influenced by various factors including dark matter, interstellar gases, star formation, and gravitational interactions. Understanding how galaxies change over billions of years requires examining several important processes and theoretical ideas.

Hierarchical Merging

One prominent theory is know as “hierarchical merging”, which states that galaxies grow and evolve through the merging of smaller structures. In the early universe, small gas clouds joined under the influence of gravity to form the first stars and proto-galaxies. These small structures merged over time, forming larger and more complex galaxies. This process continues today, as observed in galactic collisions and mergers. For example, the Milky Way is expected to collide with the Andromeda galaxy in about 4.5 billion years, eventually merging to form a new galaxy.

Secular Evolution

Secular evolution refers to the gradual transformation of galaxies due to internal processes rather than interactions with other galaxies. In spiral galaxies, this can include the redistribution of stars and gas within the disk, driven by the gravitational influence of bars and spiral arms. Over time, these processes can lead to the growth of the central bulge and the development of new spiral arms.

Star Formation

Star formation plays a key role in galactic evolution. When the gas inside a galaxy cools and condenses, it can form new stars. The energy and radiation from these stars, particularly the massive ones, can heat surrounding gas,  trigger further star formation, or even drive gas out of the galaxy in powerful winds. This feedback loop regulates the rate of star formation and shapes the galaxy’s structure over time.

The Role of Dark Matter

Dark matter, an invisible substance that makes up about 27% of the universe, plays a significant role in understanding galactic evolution. Galaxies are thought to reside within massive halos of dark matter, which provide the gravitational framework necessary for their formation and stability. Dark matter interactions can influence the distribution of galaxies and their evolution by affecting the gravitational potential pockets in which they reside.

Observable Evidence

Astronomers rely on various observational techniques to study galactic evolution. Telescopes equipped with advanced imaging and spectroscopy capabilities allow scientists to observe galaxies at different stages of their development; from the early universe to the present. By studying distant galaxies, we can look back in time and understand the conditions and processes that shaped them.

The Hubble Space Telescope and other observatories have provided detailed images of galaxies at various redshifts, revealing the morphing process and structure of galaxies over billions of years. These observations have confirmed many aspects of hierarchical merging and secular evolution theories, providing a clearer picture of how galaxies change and grow.

 

Citations:

10 Wonder Questions:

1. What happened before the big bang?
2. How did the first stars and galaxies form?
3. How do galaxies evolve over time?
4. How would humanity conduct itself if foreign life is discovered?
5. Is sending humans to Mars worth the cost? Why or why not?
6. Are there other shaped planets?
7. Why is gravity the strongest force?
8. Where is the center of the universe?
9. Is there life on other planets?
10. Are the laws of physics the same everywhere?

Reflection:

1. What questions did you need to research in order to research your topic?

• • What is the universe made of?
  • What are the different galaxy types?
  • What are the differences between galaxies?

2. What new or familiar digital tools did you try to use as you worked through this project?

• • Mostly relied on google for clarifications from google scholar papers and I used gale engage to find reliable sources to provide further information. Along the way I used Scribbr to keep track of all my citations.

3. What was the process you used to investigate the topic?

• • Firstly I had wanted to outline important information from sources that I could use to support in educating my self on the topic. On a separate document I wrote bullet points from select sites that I would later consider when formatting my blog post.

4. How did you verify and cite the information you found?

• • I only used resources that had been reliably cited and written by credible sources. Also to ensure full credibility i used gale engage from the Riverside library website.

5. How did the process of completing this challenge go? What could you have done better?

• • I could have put in more research to further convey my findings although I didn’t want to over complicate things. The topic of space is typically something I don’t favour which made it difficult to get some parts done.