There are different types of galaxies, three main types in fact, and each has its subgroups. Galaxies come in different shapes, sizes and appearances, but generally speaking, they can be organised into three distinct classes:
- Spiral galaxies
- Elliptical galaxies
- Irregular galaxies
Each of these galaxy classes has subgroups, and some galaxies are even somewhat hors catégorie; they don’t quite fit into a category.
The morphology of a galaxy refers to its visual appearance—the way it presents itself to our cosmic gaze. Imagine galaxies as celestial artworks, each with its unique brushstrokes and patterns.
To study their evolution, astronomers find it practical to classify galaxies based on their morphology. However, this task isn’t always straightforward. Why? Because the boundaries between different types of galaxies are often as elusive as stardust.
Actually, you can help with this endeavour. If you want to assist astronomers in categorising this celestial art gallery, head to galaxyzoo.org. There, you can help unravel the mysteries of these cosmic masterpieces.
With the help of volunteers, astronomers have revised their understanding of how the spiral arms of galaxies behave. It’s like a cosmic remix, where the stars dance to a new rhythm.
Let us explore the different types of galaxies
Let’s have a closer look at the three categories of galaxies, so we have a better understanding.
Spiral galaxies
In our vast cosmic canvas, spiral galaxies take centre stage. These celestial wonders are characterized by a central reddish bulge and graceful bluish spiral arms that stretch across a flat disk. Imagine them as cosmic dancers, twirling through space with periods spanning hundreds of millions of years.
The spiral arms, although they contain just 2-3 times as many stars as the spaces between them, shine brilliantly. Why? Because these regions are stellar birthplaces. This is where active star formation occurs, fueled by massive stars that burn bright with blue radiance. Their presence gives the arms their vivid blue hue.
So, when you gaze up at the night sky, remember that spiral galaxies are more than just structures—they’re celestial poems, written in stardust and illuminated by the cosmic dance of stars.
Around two-thirds of spiral galaxies flaunt a fascinating feature: a bar-like structure extending from their central bulge.
- The Bar’s Role:
- This galactic bar is similar to a density wave, as are the spiral arms themselves.
- What does it do? It has a cosmic appetite—it sucks in gas from the surrounding spiral arms.
- We can think of it as a stellar vacuum cleaner, gathering interstellar material.
- Stellar Nurseries:
- The gas drawn into the bar doesn’t go to waste. Instead, it becomes the raw material for new star formation.
- Within these bar regions, stars ignite, their brilliance illuminating the cosmic canvas.
- It’s like a celestial bakery, kneading stardust into newborn suns.
- Feeding the Cosmic Beast:
- But wait, there’s more! This gas isn’t just for stars. It can also be a cosmic feast for a supermassive black hole.
- Nestled at the galaxy’s core, this black hole devours the gas, growing into an active galactic nucleus or even a quasar.
- Imagine a cosmic dragon sipping stardust smoothies—such is the power of this feeding frenzy.
So, next time you peer through your cosmic telescope, remember that spiral galaxies aren’t just serene disks—they’re dynamic theatres where stars pirouette, bars waltz, and black holes feast
No 2 in different types of galaxies is Elliptical Galaxies
Elliptical galaxies, believed to form through the merging of smaller (proto-) galaxies, emerge from cosmic collisions. During these intense encounters, the star formation rate surges dramatically, resulting in vibrant ‘starbursts.’
However, this vigorous star formation can deplete much of the gas in one fell swoop. The collision itself, along with stellar winds and supernovae, expels the remaining gas, making it challenging for new stars to form. Consequently, only the older stars persist, and their reddish-orange hue characterizes most elliptical galaxies.
In essence, this process, aptly termed ‘quenching’, leaves behind a galaxy that appears red and ‘lifeless.’
Elliptical galaxies, colossal cosmic entities, dwarfs even our own Milky Way in terms of mass, weighing up to ten times as much. These galactic behemoths frequently take up residence at the heart of expansive galaxy clusters—vast assemblages comprising hundreds or even thousands of galaxies—bound together by the unyielding grip of gravity.
The irregular type of galaxies
Irregular galaxies, unlike other different types of galaxies, boast entirely distinct shapes. These cosmic misfits owe their irregular forms to collisions or near-misses with other galaxies.
Typically smaller in size, irregular galaxies lack the robustness of their larger counterparts, which can better withstand the gravitational tumult caused by neighbouring galaxies.
Another intriguing category is that of lenticular galaxies, blending elements of both ellipticals and spirals. These galaxies exhibit subtle spiral structures alongside a prominent elliptical halo.
Interestingly, the rarity of a galaxy increases with its size and mass. Most galaxies fall into the category of dwarf galaxies, which can be further subdivided into dwarf spirals, dwarf ellipticals, dwarf irregulars, and dwarf spheroidal galaxies.
Ring galaxies, akin to spiral galaxies, feature a central bulge and an expansive stellar ring structure. Their formation remains a mystery—perhaps a result of another galaxy ploughing straight through a spiral galaxy. However, due to their scarcity, they remain relatively unexplored.
In a recent astronomical discovery, scientists identified the most distant of these peculiar galaxies, providing evidence of a cosmic ‘hit-and-run’ event that occurred a staggering 11 billion years ago.
You can learn more about galaxies, and what they are, in a previous article here on Space Stuff Blog.
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