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PHY 1000 Unit 8 Zoo of Galaxies


Galaxies are majestic celestial structures that captivate our imaginations and offer glimpses into the vastness of the universe. They are the building blocks of the cosmos, each housing billions or even trillions of stars along with countless other celestial objects. Let us delve deeper into the three main types of galaxies: spiral, elliptical, and irregular.

Spiral Galaxy:

Among the diverse galaxies, spiral galaxies reign as the most common type, comprising over 75% of all known universes. They possess a captivating beauty with their graceful, swirling arms and pronounced core. The spiral arms of these galaxies exhibit a high rate of star formation, with hot, young stars illuminating their surroundings. These galaxies are also relatively young, containing copious amounts of gas and dust, serving as new stars’ birthplaces.

PHY 1000 Unit 8 Zoo of Galaxies

What distinguishes spiral galaxies is their vibrant colors, which reflect the different stages of star development within them. In the tapestry of a spiral galaxy, red hues mark the presence of older stars nearing the end of their lives, while blue regions signify the birth of young, energetic stars. This color variation is akin to excavating Earth’s soil, where the deeper one digs, the more prosperous and diverse the layers become due to the accumulation of minerals over time.

Spiral galaxies exhibit a range of forms. Some appear as tightly wound spirals, where discerning the individual arms can be challenging. Others showcase a more moderate winding, gradually revealing their distinct components. Lastly, loosely wound spirals proudly unveil their outstretched arms emanating from the central bulge. Notably, our heavenly abode, the Milky Way galaxy, shares many similarities with a typical spiral galaxy.

Elliptical Galaxy:

In contrast to the mesmerizing spirals, elliptical galaxies exude a different aura of grandeur. These galaxies are the largest entities in the universe, boasting masses exceeding 10 billion solar masses. Unlike their spiral counterparts, elliptical galaxies lack intricate arms and graceful swirls. Instead, they adopt a rounded or elongated shape reminiscent of a bulge.

PHY 1000 Unit 8 Zoo of Galaxies

Elliptical galaxies present a stark contrast in terms of star formation and composition. They consist of minimal amounts, if any, of gas and dust. Consequently, they display no discernible signs of young star creation. Instead, the stars within these galaxies are predominantly aging, nearing the twilight of their existence. 

The color palette of elliptical galaxies tends to lean towards red, owing to the prevalence of low-mass, older stars. The lack of gas and interstellar dust required for new star formation indicates that these galaxies have depleted their fuel and are gradually waning.

Irregular Galaxy:

Nature always holds a few surprises, and irregular galaxies embody that sense of wonderment. These galaxies defy the structured elegance of spirals and the rounded contours of ellipticals. Irregular galaxies are characterized by their peculiar, asymmetrical shapes and chaotic appearance. Their distorted forms can range from a mishmash of twisted arms to a cigar-shaped structure with a cloud-like formation at one end, reminiscent of smoke drifting away.

Irregular galaxies represent the outliers, accounting for less than 5% of all known galaxies. They are often the smallest and least luminous members of the galactic family. However, what sets them apart is their inherent youthfulness. Irregular galaxies harbor the newest generation of stars, with environments rich in interstellar dust and gases. These cosmic nurseries are the birthplaces of countless young stars, painting the galaxy with a vibrant blue hue.

PHY 1000 Unit 8 Zoo of Galaxies

Within the realm of irregular galaxies, two primary classifications emerge. Irr I galaxies consist predominantly of blue stars, indicating their youthful nature. These galaxies are brimming with stellar activity as new stars burst into existence.

 On the other hand, Irr II galaxies exhibit peculiar characteristics resulting from recent explosive events or close encounters with neighboring stars or galaxies. Among these rare curiosities, a notable example is the Starburst galaxy, known for its intensely bright and active core. The star clusters within this galaxy outshine anything found within our own Milky Way, radiating brilliantly across the entire spectrum of colors.

Our Universe:

Contemplating the universe’s grand tapestry and its evolution is an awe-inspiring journey. As we unravel the mysteries of the cosmos, we encounter an ever-changing landscape of cosmic wonders. 

Our understanding of the universe has evolved from ancient stargazers who marveled at the brightness in the night sky to the sophisticated telescopes in space, enabling us to peer deep into the cosmic abyss. Unmanned satellites embark on audacious missions, pushing the boundaries of exploration with hopes of reaching the edge of our galaxy and venturing even further into the unknown.

PHY 1000 Unit 8 Zoo of Galaxies

Just as ancient civilizations discovered that the Earth is not flat and that we are not the center of the universe, our pursuit of knowledge continues unabated. We persistently strive to comprehend the intricate workings of the universe by observing, analyzing, and theorizing. 

Billions of years have culminated in our present understanding. With ever-advancing scientific achievements, we anticipate that Earth will endure for billions more, providing ample time for us to unravel other cosmic secrets and expand our intellectual horizons.

The galaxies’ diverse forms and mesmerizing features serve as beacons of inspiration and remind us of the infinite possibilities that await discovery. They beckon us to gaze skyward, ponder our place in the vast cosmos expanse, and embark on an unending quest for knowledge and understanding.


Airapetian, V. S. (2014). Rocking stories of the universe. Dubuque, IA: Great River Learning


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