Spiral Galaxy vs Elliptical Galaxy Difference: A Complete Beginner-Friendly Guide
Introduction
The spiral galaxy vs elliptical galaxy difference is an important topic in astronomy. These two galaxy types have different shapes, structures, star populations, and amounts of gas and dust.
Galaxies are enormous systems held together by gravity. They contain stars, gas, dust, planets, and dark matter. Most large galaxies also have a supermassive black hole at their center. (NASA Science)
Scientists classify galaxies partly by their visible shapes. Spiral galaxies have broad disks and curved arms, while elliptical galaxies look more rounded or oval and have much less visible structure. (NASA Science)
These differences can also tell astronomers about how galaxies form and change over time. By studying their stars, gas, dust, and motion, scientists can learn more about the history of the universe.
In this guide, we will compare spiral and elliptical galaxies in simple terms. We will also look at their structures, star formation, gas content, and possible evolutionary paths.
What Is a Galaxy?
A galaxy is a huge gravitational system containing stars and other forms of matter.
Galaxies can contain billions or even trillions of stars. They also contain gas and dust that can provide the raw materials needed to form new stars. Dark matter adds much more mass, although it cannot be seen directly with ordinary light. (NASA Science)
Astronomers classify galaxies into several broad groups. The familiar categories include spiral, elliptical, and irregular galaxies. Lenticular galaxies form another important category between some spiral and elliptical features. (NASA Science)
Our home galaxy, the Milky Way, is a spiral galaxy. The nearby Andromeda Galaxy, also known as M31, is another major spiral galaxy. NASA lists Andromeda as the nearest major galaxy to the Milky Way at about 2.5 million light-years away. (NASA Science)
Understanding these galaxy types helps scientists compare different environments across the universe.
What Is a Spiral Galaxy?
A spiral galaxy has a broad, rotating disk with curved arms extending from a central region.
These galaxies often contain large amounts of gas and dust, especially within their spiral arms. That material can support the formation of new stars. As a result, spiral galaxies can contain both young and old stellar populations. (NASA Science)
The Milky Way is an example of a barred spiral galaxy. Andromeda is also a spiral galaxy, although its structure is not identical to that of the Milky Way. (NASA Science)
Main Features of Spiral Galaxies
Spiral galaxies commonly have several recognizable features.
A Flat Disk
The main body of a spiral galaxy is a relatively flat disk containing stars, gas, and dust.
From a face-on view, the disk can look like a giant pinwheel. However, the shape can be harder to recognize when the galaxy is viewed from the side.
Spiral Arms
The curved arms are one of the most obvious features of a spiral galaxy.
These regions often contain significant amounts of gas and dust. They can also contain many young, bright stars and star-forming regions. (NASA Science)
The arms are not simply solid structures that rotate like the blades of a fan. They are patterns within the galaxy’s disk, and stars can move through these patterns.
Central Bulge
Many spiral galaxies have a dense central bulge.
The bulge contains a high concentration of stars and is generally dominated by older stellar populations.
In barred spiral galaxies, a long bar of stars crosses the central region. The spiral arms can begin near the ends of this bar. (NASA Science)
Halo
A spiral galaxy also has a much larger, fainter halo surrounding its main disk.
The halo can contain older stars and star clusters. It is also associated with a large amount of dark matter.
Example: The Milky Way
The Milky Way is our home galaxy and is classified as a barred spiral galaxy.
We cannot photograph it from outside because our Solar System is inside the galaxy’s disk. Instead, astronomers study its stars and other material from within the Milky Way.
The galaxy contains a central bulge, a disk, spiral structure, and a surrounding halo.
Studying the Milky Way helps scientists understand how spiral galaxies work. It also gives us a useful reference when comparing our galaxy with other galaxies.
Example: The Andromeda Galaxy
The Andromeda Galaxy is another major spiral galaxy.
It is about 2.5 million light-years from Earth and is the nearest major galaxy to the Milky Way. NASA’s Hubble observations show its broad disk and spiral structure in great detail. (NASA Science)
Andromeda is useful for studying spiral galaxies because astronomers can observe it from outside. This gives scientists a different view from what we can obtain from inside the Milky Way.
Why Spiral Galaxies Can Form New Stars
Gas and dust are important ingredients for star formation.
Spiral galaxies often retain more of this cold material than elliptical galaxies. Their disks therefore contain regions where new stars can form.
The youngest stars are often found in or near the spiral arms, while older stars are also present in the bulge, disk, and halo. (NASA Science)
This mixture of young and old stars gives spiral galaxies a different appearance and history from many elliptical galaxies.
A Useful AstroNive Connection
Galaxy structure is also connected to the larger-scale movement of matter through the universe.
If you want to explore another example of how large-scale gravity affects galaxies and their surroundings, read AstroNive’s guide to The Great Attractor and the cosmic force pulling galaxies.
This helps put individual galaxies into the wider picture of cosmic structure.
What Makes Spiral Galaxies Different?
The main feature that separates spiral galaxies from elliptical galaxies is their structure.
Spiral galaxies have organized disks and arms. They also tend to contain more gas and dust, which allows ongoing star formation.
Elliptical galaxies have much smoother shapes and generally contain older stars with less ongoing star formation. (NASA Science)
However, the difference is more than appearance.
Galaxy shape is connected to its history, stellar population, gas supply, and interactions with other galaxies.
That is why astronomers study galaxy structure when trying to understand how galaxies evolve.
Spiral Galaxies Are Not All the Same
Not every spiral galaxy looks identical.
Some have tightly wound arms, while others have more open arms. Some have a strong central bar, while others do not.
Astronomers use different classification systems to describe these variations. The classic Hubble classification separates spiral galaxies into several forms based partly on the appearance of their arms and central regions. (NASA Science)
This means that “spiral galaxy” describes a broad family rather than one exact shape.
In the next part, we will look closely at elliptical galaxies and then compare the two galaxy types by shape, stars, gas, dust, motion, and formation.
What Is an Elliptical Galaxy?
An elliptical galaxy has a smooth, rounded, or oval appearance. Unlike a spiral galaxy, it does not have visible spiral arms or a prominent flat disk.
These galaxies can range from relatively small systems to enormous galaxies containing vast numbers of stars. Their stars are generally older, and they usually contain much less cold gas and dust than star-forming spiral galaxies. NASA: Types of Galaxies
Main Features of Elliptical Galaxies
Elliptical galaxies have several features that make them different from spiral galaxies.
Smooth Shape
Their most obvious feature is their smooth appearance.
An elliptical galaxy may look almost spherical or strongly stretched into an oval shape. Astronomers classify elliptical galaxies partly by how elongated they appear.
Older Stars
Elliptical galaxies are generally dominated by older stars.
Because they usually contain little cold gas and dust, they have much less ongoing star formation than typical spiral galaxies. NASA: Types of Galaxies
Little Cold Gas and Dust
Gas is an important raw material for making new stars.
Many elliptical galaxies have relatively little cold gas available for star formation. As a result, they often appear less blue than galaxies with large populations of young stars.
Different Stellar Motion
The stars in a spiral galaxy mainly follow organized motion around its disk.
In elliptical galaxies, stellar orbits are generally more varied and less dominated by one common direction of rotation.
This difference in motion is another important part of the spiral galaxy vs elliptical galaxy difference.
Example: Messier 87
Messier 87, or M87, is a famous giant elliptical galaxy in the Virgo Cluster.
It is especially well known because scientists have studied the supermassive black hole at its center. The Event Horizon Telescope produced the first direct image of a black hole’s shadow in M87 in 2019.
M87 shows why elliptical galaxies can be important laboratories for studying massive galaxies, black holes, and galaxy clusters.
What Is an Elliptical Galaxy?
An elliptical galaxy has a smooth, rounded, or oval shape. Unlike a spiral galaxy, it does not have visible spiral arms or a prominent flat disk.
These galaxies can range from relatively small systems to enormous galaxies containing vast numbers of stars. They generally contain older stars and much less cold gas and dust than actively star-forming spiral galaxies. NASA: Types of Galaxies
Main Features of Elliptical Galaxies
The most obvious feature is their smooth appearance. Some elliptical galaxies look almost spherical, while others are noticeably stretched into an oval shape.
They are also dominated by older stars. Because they usually contain less cold gas and dust, they generally have much less ongoing star formation than spiral galaxies. NASA: Types of Galaxies
Their stars also move differently from those in a spiral galaxy. Stars in a spiral galaxy mainly follow organized motion around its disk. In an elliptical galaxy, stellar orbits are more varied and are not dominated by one common direction of rotation.
Example: Messier 87
Messier 87, or M87, is a famous giant elliptical galaxy in the Virgo Cluster.
It is especially well known because scientists have studied the supermassive black hole at its center. In 2019, the Event Horizon Telescope produced the first image of a black hole’s shadow, located in the center of M87.
M87 shows why elliptical galaxies are important for studying massive galaxies, black holes, and galaxy clusters.
How Do Elliptical Galaxies Form?
The formation of elliptical galaxies is more complex than simply saying that two spiral galaxies collide.
Galaxy mergers can strongly disturb galactic disks and change their structure. A major merger can produce a system with much less organized disk structure.
However, not every elliptical galaxy necessarily formed through one specific type of collision.
Galaxies can grow through different processes, including mergers, gravitational interactions, and the gradual accumulation of material over cosmic time.
Therefore, astronomers study the stars, gas, motion, and surrounding environment of individual galaxies to understand their histories.
Spiral Galaxy vs Elliptical Galaxy: Key Differences
The clearest way to understand the difference is to compare their main properties.
| Feature | Spiral Galaxy | Elliptical Galaxy |
|---|---|---|
| Shape | Disk with spiral arms | Smooth, rounded, or oval |
| Gas and dust | Often more abundant | Usually much less cold gas and dust |
| Star formation | Often active | Usually low |
| Stars | Young and old populations | Mostly older stars |
| Stellar motion | Strong organized rotation in the disk | More varied stellar orbits |
| Main structure | Disk, bulge, and halo | Smooth stellar distribution |
| Examples | Milky Way, Andromeda | M87 |
These are broad patterns rather than absolute rules. Some galaxies have unusual properties and may not fit neatly into one simple category.
Can a Spiral Galaxy Become an Elliptical Galaxy?
A spiral galaxy can lose much of its disk structure through major gravitational interactions, including some galaxy mergers.
When galaxies interact, their gravity can disturb their stars and gas. A major merger can create a more chaotic stellar system and may contribute to the formation of an elliptical galaxy.
However, galaxy evolution is not always a simple process of spiral → collision → elliptical.
Scientists now understand galaxy evolution as the result of many different processes. Some galaxies merge, while others interact without completely merging. Gas can also cool, heat up, or be removed from a galaxy.
The surrounding environment can influence these changes as well.
That is why astronomers study galaxy populations across different periods of cosmic history rather than relying on one formation pathway.
Why Does the Difference Matter?
The difference between spiral and elliptical galaxies gives scientists clues about their past.
A spiral galaxy with large amounts of gas and young stars may still be actively forming new stars. An elliptical galaxy dominated by old stars may have experienced a different evolutionary history in which star formation became much weaker.
Studying both types allows astronomers to compare different environments and stages of galaxy evolution.
It also connects to a larger question: how did galaxies change from the early universe into the enormous structures we see today?
Similarities Between Spiral and Elliptical Galaxies
Although spiral and elliptical galaxies look very different, they share several basic features.
Both are large gravitational systems containing stars and other matter. They can contain billions of stars and can have supermassive black holes at their centers.
Both galaxy types are also influenced by dark matter. Although dark matter cannot be observed directly with ordinary light, its gravitational effects help scientists understand how galaxies move and remain bound together.
These similarities show that galaxy classification is mainly about their structure and properties, not completely different types of objects.
Which Galaxy Type Has More Star Formation?
Spiral galaxies generally have more active star formation than elliptical galaxies.
Their disks often contain cold gas and dust. This material provides the ingredients needed to create new stars.
Elliptical galaxies usually contain much less cold gas. Therefore, their star formation is generally much weaker.
However, this does not mean that every spiral galaxy is actively forming stars or that every elliptical galaxy has completely stopped forming them. Individual galaxies can have unusual conditions.
Which Galaxy Is Older?
It is better to compare their stellar populations rather than simply saying that one galaxy type is older.
Elliptical galaxies generally contain a larger population of old stars. Spiral galaxies often contain both old and young stars because they can continue forming new stars.
This difference provides important clues about the history of each galaxy.
Are Spiral Galaxies More Common Than Elliptical Galaxies?
The answer depends on the population being studied and how galaxies are classified.
Spiral galaxies are common in the nearby universe, but elliptical galaxies are also an important part of the galaxy population. Large elliptical galaxies are particularly common in dense environments such as galaxy clusters.
Astronomers therefore study the distribution of different galaxy types to understand how their environments affect galaxy evolution.
Why Do Galaxy Shapes Matter?
Galaxy shape is more than a visual feature.
A galaxy’s structure can reveal information about its history, including how it formed stars, how much gas it retained, and whether it experienced interactions with other galaxies.
For example, a well-defined spiral disk suggests a different evolutionary history from the smooth structure of a giant elliptical galaxy.
By comparing these systems, astronomers can build a better picture of how galaxies change over billions of years.
Frequently Asked Questions
What is the main spiral galaxy vs elliptical galaxy difference?
The main difference is their structure. Spiral galaxies have a flattened disk and spiral arms, while elliptical galaxies have a smoother, rounded or oval shape.
Which galaxy type has more young stars?
Spiral galaxies generally have more young stars because they usually contain more gas and dust that can support ongoing star formation.
Which galaxy type contains mostly old stars?
Elliptical galaxies generally contain mostly older stars and have much lower levels of ongoing star formation.
Can a spiral galaxy become an elliptical galaxy?
A major galaxy merger can destroy or greatly disturb a spiral galaxy’s disk and contribute to the formation of an elliptical galaxy. However, galaxy evolution involves several different processes.
Is the Milky Way a spiral galaxy?
Yes. The Milky Way is a barred spiral galaxy.
Is Andromeda a spiral galaxy?
Yes. The Andromeda Galaxy, also called M31, is a major spiral galaxy located about 2.5 million light-years from Earth. NASA: Messier 31
Is M87 an elliptical galaxy?
Yes. Messier 87 is a giant elliptical galaxy in the Virgo Cluster. It is also famous for the supermassive black hole at its center.
Do elliptical galaxies have black holes?
Many large galaxies, including elliptical galaxies, contain supermassive black holes at their centers.
Conclusion
The spiral galaxy vs elliptical galaxy difference can be understood by looking at their shape, stars, gas, dust, motion, and star formation.
Spiral galaxies have flattened disks and spiral arms. They often contain significant amounts of gas and dust and can continue forming new stars.
Elliptical galaxies have smoother shapes and generally contain older stellar populations. They usually have much less cold gas and therefore show less ongoing star formation.
However, these galaxies are not completely separate from one another. Galaxy interactions and mergers can change their structures over time.
Understanding these differences helps astronomers study galaxy formation and evolution. It also shows how the universe can produce many different structures from the same basic ingredients of matter and gravity.
For readers who want to explore more galaxy-related topics, AstroNive’s guide to elliptical galaxies provides a deeper look at this important galaxy type.
Trusted Sources for Further Reading
For more information, NASA’s guide to galaxy types explains the major galaxy classifications and their basic characteristics.
The European Space Agency’s Hubble glossary entry on elliptical galaxies also provides useful background on elliptical galaxy structure.
These sources can help readers explore galaxy classification and evolution beyond this beginner-friendly guide.
jafir
Jafir Abbas is the visionary founder and owner of Astronive.com, a leading online hub for astronomy enthusiasts, space exploration insights, and cosmic discoveries. With a passion for the mysteries of the universe, Jafir has dedicated his work to making complex astronomical concepts accessible and engaging for readers of all ages. Under his guidance, Astronive.com has become a trusted resource for space news, celestial events, and educational content that inspires curiosity about the cosmos. Jafir combines a keen interest in science with a commitment to clear, engaging communication, bringing the wonders of the universe closer to everyone.
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