Why Do Galaxies Have Different Shapes?

September 29, 2026

Four contrasting galaxy forms, including spiral, elliptical, edge-on and irregular structures, connected by delicate orbital lines in deep space.

Journal Information

Universe:

Cosmos

Focus:

Galaxies, Form, Movement, Scale and Visual Culture

Reading Time:

22 Minutes

"When we look at a galaxy, we may see vast spiral arms opening outwards from the centre, a smooth and almost perfectly oval structure, or scattered regions of stars with no obvious order. At first glance, these may appear to be simply different visual forms, but the appearance of a galaxy can carry traces of the stars, gas, dust, movement and past interactions within it. Trying to understand why these enormous systems of billions of stars look so different from one another can tell us a great deal not only about astronomy, but also about how movement and scale become visible. Perhaps this is one reason galaxies are so compelling: their forms may appear like fixed symbols, yet they are actually the result of movements unfolding across immense periods of time."

Why Do Galaxies Have Different Shapes?

Not every galaxy in the sky has the same basic visual structure. Some show clearly defined arms extending from a bright centre, while others display a smoother and more oval distribution of stars. In some galaxies, identifying a clear centre, arm structure or symmetry is much more difficult. To understand these differences, it is useful to think of a galaxy not simply as a vast collection of stars sitting in the distance, but as an enormous system in constant motion.

The appearance of a galaxy can be connected to the distribution of its stars, the amount of gas and dust it contains, where star formation is concentrated and how the galaxy itself moves. Close encounters or mergers with other galaxies can also alter its form over time. Galaxy classifications therefore tell us more than simply “what does it look like?” They can also provide clues about the physical structure and history of the system.

The form of a galaxy is not decoration.

It is one of the visible parts of its story.

What Makes a Galaxy a Galaxy?

A galaxy is not simply made of stars that happen to appear close together. Stars, stellar systems, gas, dust and enormous amounts of unseen matter move within the same large system under the influence of gravity. Galaxies can contain millions of stars, while the largest systems may hold hundreds of billions.

Gravity is the fundamental force that allows such an enormous structure to remain together. Stars and gas in different parts of the galaxy move under the influence of its overall mass distribution. This does not mean, however, that every star follows the same path. Depending on the structure of the galaxy, stellar orbits and patterns of movement can vary considerably.

When we look at a galaxy, then, we are actually seeing a large-scale form produced by billions of separate motions working together. A spiral arm, an oval body or an irregular distribution of stars is not the surface of a single object. It is the image produced by countless stars and other forms of matter moving within the same system over immense periods of time.

Why Do Spiral Galaxies Look Like Rotating Vortices?

Spiral galaxies are among the most recognisable structures in cosmic imagery. Arms opening outwards from a bright central region can give the galaxy the appearance of an enormous rotating vortex. The Milky Way is also classified as a barred spiral galaxy, and the Solar System lies within this vast structure.

It would be misleading to imagine spiral arms as fixed chains of stars permanently attached to the centre of a galaxy. Stars and gas move through the galaxy while the larger spiral structure can remain visible. The arms often make regions rich in dense gas, dust and young stars more noticeable, which is why bright areas of star formation can make the spiral pattern particularly clear.

As the galaxy rotates over billions of years, individual stars continue along their own orbits. The spiral we see is therefore not a completely fixed pattern. It is more useful to think of it as a temporary yet persistent visual order within a system moving across enormous timescales.

For the human eye, this structure is particularly powerful. Spiral arms naturally guide our attention from the outer regions towards the centre, then back outwards again, producing a strong sense of movement.

Why Do Spiral Arms Not Rotate as a Single Solid Form With the Entire Galaxy?

If we imagine a spiral galaxy as a pattern painted onto a rotating plate, we miss an important detail. The stars and gas within a galaxy are not attached to a solid surface moving at one angular speed. Matter in the inner and outer regions can follow different orbital motions.

Density waves are one important concept used to explain spiral structure. In simplified terms, stars and gas may move through denser regions that make the spiral arms more visible. In the same way that the individual cars within a traffic jam continually change while the area of congestion remains visible, the stars within a spiral arm can change over time while the larger structure persists.

This comparison does not explain every detail, but it helps us understand an important point. Spiral arms do not need to consist of exactly the same stars remaining together for billions of years. They can be dynamic regions where galactic movement and star formation come together.

The form we see therefore exists despite movement.

Or perhaps more accurately, it exists because of movement.

What Is a Barred Spiral Galaxy?

Some spiral galaxies contain a long bar of stars across their central region rather than a purely rounded centre. Spiral arms can extend outwards from the ends of this central bar. These systems are known as barred spiral galaxies, and the Milky Way is also thought to possess such a central structure.

A galactic bar is not merely a visual detail. It can influence the movement of stars and gas and may help transport gas towards the inner regions of the galaxy. This can affect star formation near the centre and contribute to the long-term structure of the galaxy.

Visually, the bar also changes the symmetry of the spiral galaxy. The arms may feel as though they emerge not from a single round centre, but from a horizontal or angled main structure. The same basic spiral idea therefore gains a different rhythm.

This distinction matters within the visual language of the cosmos. Even within the same broad class of galaxy, there is no single standard form.

Why Do Elliptical Galaxies Not Have Spiral Arms?

Elliptical galaxies look very different from the clearly defined discs and arms of spiral galaxies. They may be nearly round or stretched into long oval shapes, and their stars generally form a smoother distribution of light that becomes more concentrated towards the centre. At first glance they can appear simpler than spiral galaxies, but that visual simplicity does not mean they are physically simple.

The stars in these galaxies can move in more varied directions rather than following the more orderly circular motion associated with a disc. Many elliptical galaxies also contain less cold gas and star-forming material than spiral galaxies, which can limit the formation of new stars. A significant part of their light may therefore come from older stellar populations.

Some elliptical galaxies are thought to be connected with past galaxy mergers. When two large galaxies interact and merge, their previous organised disc structures can be disrupted and the orbits of their stars can become more complex. Long after the system settles, the result may be a large, smooth distribution of stars without visible spiral arms.

From this perspective, an elliptical form does not mean that order is absent.

It may represent a different kind of order.

Why Do Lenticular Galaxies Seem to Sit Between Two Different Worlds?

Lenticular galaxies can appear to occupy a visual space between spiral and elliptical galaxies. They can possess a disc and central bulge, yet lack clearly defined spiral arms. From a distance, they may therefore resemble both the flat disc of a spiral galaxy and the smoother appearance of an elliptical galaxy.

These galaxies often contain less cold gas for forming new stars than spiral galaxies. Their discs may remain visible even though the bright young stars that normally help define spiral arms are absent or much less prominent. The overall form can remain while the activity within it changes character.

There is no single process that explains how every lenticular galaxy reached this structure. Gas loss, environmental effects or past interactions may play different roles in different systems. As is often the case with cosmic classifications, belonging to a category does not mean that every member of that category shares exactly the same history.

This again shows why galaxy shapes should not be treated as purely superficial classifications.

Is an Irregular Galaxy Really Irregular?

The phrase “irregular galaxy” may initially suggest that the galaxy has no structure at all. In reality, the term usually means that the galaxy cannot easily be placed within a clear large-scale form such as a spiral or elliptical galaxy. Regions of star formation, gas clouds and bright clusters are still present, but they may not be organised within a symmetrical disc or smooth oval body.

The appearance of some irregular galaxies may have been influenced by the gravity of a nearby galaxy or by a past encounter. Other systems may never have resembled large spiral galaxies because of their smaller masses and different internal structures. “Irregular” therefore does not describe one single physical history.

Visually, irregular galaxies are especially interesting because they disrupt the symmetry our eyes can easily recognise. In a spiral galaxy we can follow arms towards the centre, while an elliptical galaxy offers an overall oval unity. In an irregular galaxy, the eye may need to form its own connections between different bright regions and clouds of gas.

Perhaps this is why they can carry such a strong visual character despite appearing chaotic.

Can Galaxies Collide With One Another?

Yes. Although the scale of the universe is enormous, galaxies are not completely isolated from one another. Systems within the same galaxy groups and clusters can approach each other under the influence of gravity, experience close encounters and eventually merge.

The phrase “galaxy collision” can sound as though billions of stars are crashing directly into one another in an enormous catastrophe. Yet the distances between stars are so vast that direct physical collisions between individual stars are relatively unlikely when two galaxies merge. The greater effect comes from the overall gravitational fields of the galaxies reshaping the distribution of stars, gas and dust.

Gas clouds can be compressed, new regions of star formation may appear and long streams of stars can extend away from the galaxies. An initially organised spiral structure may become distorted, and an entirely different system may emerge by the end of the merger.

Galactic interactions are among the clearest examples showing that form is not permanent on cosmic scales.

Why Do Galaxies Become Distorted When They Approach One Another?

Gravity becomes increasingly influential as distance decreases. When two galaxies approach one another, different regions of each galaxy are not affected by the other galaxy’s gravity to exactly the same degree. These differences can pull stars and gas away from their previous orbits.

As a result, long tails extending away from the galaxies, bridges of stars or irregular bright regions may appear. Such structures can be among the clearest visible signs of a galactic interaction. A galaxy can temporarily lose a shape that once appeared balanced.

It would be incomplete, however, to understand this distortion only as destruction. Compressed gas can accelerate the formation of new stars, and a completely new large-scale structure may emerge after the merger. On cosmic timescales, form can be disrupted, rearranged and eventually reach another state of balance.

The shape of a galaxy therefore behaves less like a still photograph and more like a single moment within a very long process.

Is the Shape of a Galaxy Really the Shape We See?

When trying to understand the appearance of a galaxy, we also need to consider our own viewing angle. Galaxies are three-dimensional structures, yet telescope images present them to us across a two-dimensional surface. The angle at which a galaxy is oriented towards us can therefore change its appearance considerably.

If we are looking towards the face of a spiral galaxy, its arms may be clearly visible. Another galaxy of the same type viewed edge-on can appear as a narrow, elongated band of light because many of its arms overlap along our line of sight. Its central region may then appear as a brighter bulge within the middle of the disc.

Two galaxies that look completely different therefore do not necessarily have completely different underlying structures. Part of the difference may be physical, while another part may come from viewing angle.

When we observe the universe, there is always a perspective between the image we see and the structure we are looking at.

How Do We Know the Shape of the Milky Way?

The Milky Way presents an interesting problem because we cannot observe our galaxy from the outside. We are inside it. When we look towards the pale band of stars stretching across the night sky, we are actually viewing a dense region of the galactic disc from our position within it.

Understanding the overall structure of the Milky Way requires astronomers to combine the positions and motions of stars with maps of gas distribution and observations across different wavelengths. Dense dust blocks visible light towards the galactic centre, so infrared and radio observations can provide important information about its structure.

These studies show that the Milky Way has a spiral structure with a bar of stars across its centre. Yet it is important to remember that the “external views” of the Milky Way we often see online are not photographs taken from outside our galaxy. We have not yet travelled far enough away to photograph it from such a viewpoint.

This reminds us of another important distinction when looking at space imagery:

Observation, model and artistic visualisation are not the same thing.

Is There a Relationship Between Galaxy Colour and Galaxy Shape?

The overall colour of a galaxy can provide clues about its stellar populations and star formation. Regions where new stars are forming intensely can appear more blue because of very hot, young stars. Areas dominated by older stellar populations may instead lean towards warmer yellow and red tones.

This is one reason the arms of spiral galaxies can appear bluer in some images while their central regions look more yellow. Spiral arms can contain gas and young star-forming regions, while older stellar populations may be more concentrated towards the galactic centre. In elliptical galaxies, where new star formation is more limited, the overall colour can also lean towards warmer tones.

However, it is important to remember what we previously discussed about colours in space imagery. The colours used in telescope images do not always correspond to the colours the human eye would naturally perceive. The wavelengths selected and the way the data is processed can alter the visual character of the final image.

The colour of a galaxy, like its shape, should therefore be considered with an understanding of how the image was produced.

Why Can the Centre of a Galaxy Appear So Bright?

In many galaxies, the central region appears brighter than its surroundings because the density of stars can increase towards the inner areas. Large numbers of stars concentrated within a relatively small region of the sky can turn the centre into a powerful source of light. In some galaxies, material surrounding an active supermassive black hole can also produce extraordinary brightness.

Not every bright galactic centre, however, indicates an active black hole. A high concentration of stars can produce substantial central brightness on its own. This distinction is particularly important when interpreting images because it would not always be accurate to connect a bright core directly with one specific physical process.

From the perspective of graphic design, a bright galactic centre offers a remarkably strong natural focal point. As the arms extend outwards, the eye is drawn back towards the luminous region at the centre. Light, movement and scale can come together within the same composition.

Perhaps this is one reason spiral galaxies appear so frequently within visual culture.

They almost tell us where to look.

Why Are Spiral Galaxies So Visually Powerful?

The human eye naturally follows movement, and spiral structures can produce this effect even within a still image. Curving arms can appear to rotate around the centre, encouraging the eye to follow the same paths. The composition can therefore suggest movement even though the image itself is not moving.

A spiral also establishes a clear relationship between centre and surrounding space. The bright core becomes the focal point while the arms expand the image outwards and allow us to feel the scale of the galaxy. Dark regions between the arms can make brighter star fields appear even more distinct.

This relationship can also become a powerful tool within cosmic graphic design. The centre, arms, empty space and surrounding stars stop feeling like separate details and begin to act as parts of the same movement. When used effectively, the eye can naturally understand where to pause and which direction to follow within the design.

A scientific structure can therefore also provide a powerful visual language.

Does Every Galaxy Have a Black Hole at Its Centre?

Supermassive black holes are thought to be extremely common at the centres of large galaxies, and the Milky Way contains the supermassive black hole Sagittarius A* at its centre. It would be inaccurate, however, to assume that the general form of a galaxy is determined only by its central black hole.

Although the mass of a central black hole can be enormous, the total mass of the galaxy is far greater. Stars, gas and dark matter all contribute to the gravitational structure of the entire system. Connecting the existence of spiral arms or the general galactic disc only to the central black hole would therefore be incomplete.

Active central black holes can, however, influence the gas within a galaxy. Powerful energy outflows may change the behaviour of surrounding matter and affect star formation over long periods.

The relationship between a galaxy and its central black hole is therefore neither simple nor one-directional.

Does Dark Matter Affect the Shape of a Galaxy?

We know that galaxies are not made only from the stars and gas we can see. The motion of stars within galaxies and other observations indicate that far more mass is present than visible matter alone can account for. We refer to this unseen component as dark matter.

Dark matter does not emit light or reflect it in the ordinary way, so it does not appear directly within telescope images. Yet the gravity of the enormous dark matter haloes thought to surround galaxies influences the motion of stars and gas and plays a fundamental role in the formation and structure of galaxies.

This is particularly compelling because a significant part of the structure we can see exists under the influence of a mass distribution we cannot see. We can observe a spiral arm, measure starlight and examine regions of gas, yet much of the mass shaping the entire system remains invisible to us.

The cosmos gives us the same lesson again.

The visible structure is not always the whole story.

Do Galaxies Differ in Size as Much as They Differ in Shape?

Yes. Galaxies vary enormously not only in form but also in size. Small dwarf galaxies may contain relatively few stars, while large galaxies can hold hundreds of billions or even more.

Physical size and visual complexity, however, are not always the same thing. A small irregular galaxy can appear extremely complex because of active star-forming regions, while a very large elliptical galaxy may look relatively simple from a distance, appearing as a smooth oval field of light.

This shows how easily human perception can be misled when judging scale. A galaxy that appears small in the sky may in reality extend across hundreds of thousands of light-years. Apparent size within an image does not directly reveal physical size because distance also affects how large an object looks.

Scale in cosmic imagery therefore needs context, not just numbers.

Do Galaxy Shapes Change Over Time?

Yes. Galaxies are not unchanging sculptures. Their stars move, gas is consumed or redistributed, new stars form, older stars reach the ends of their lives and galaxies can interact with other systems.

These changes do not happen quickly enough for us to watch most of them unfold directly during a human lifetime. Many galactic processes take place across millions or billions of years. A single telescope image can therefore make a galaxy appear almost motionless even though the system itself exists within a long process of change.

The shape of a galaxy as we see it today is therefore not necessarily its final form. It is both the result of its past and one stage in a system that may take on another form in the future.

A photograph of a galaxy freezes the movement.

The galaxy keeps moving.

When We Look at Very Distant Galaxies, Are We Actually Looking Into the Past?

Because light takes time to reach us, when we observe a distant galaxy we do not see it exactly as it exists now. Light from a galaxy millions of light-years away has travelled for millions of years before reaching us. With much more distant systems, we may be looking at galaxies as they existed billions of years ago.

Observing the distant universe through telescopes is therefore also a way of studying the cosmic past. Galaxies in the early universe can appear different and more irregular than many nearby galaxies, helping us understand how galactic structures have changed across time.

This adds another dimension to the idea of galaxy shape. By looking at different distances at the same time, we are also comparing galaxy structures from different periods in cosmic history. The cosmos is not only vast in space.

It is deep in time as well.

Why Is It Useful to Classify Galaxy Shapes?

Dividing galaxies into categories such as spiral, elliptical, lenticular or irregular may initially look like nothing more than a visual sorting system. Classification, however, allows us to compare systems with similar physical properties across enormous amounts of observational data.

Connections can exist between certain forms and star formation, gas content, stellar populations and environmental conditions. Knowing the shape of a galaxy does not explain its entire history, but it can help researchers identify more useful questions to investigate.

Classifications also have limits. Real galaxies do not always fit neatly into clean categories, and some systems can contain several structural features at once. It is therefore more useful to think of classification not as nature itself, but as a human tool that helps us understand natural complexity.

Names do not change the universe.

They give us a shared language through which we can talk about it.

What Can Different Galaxy Shapes Offer Cosmic Design?

When we think of galaxies not only as astronomical systems but also as visual structures, an exceptionally broad language appears. A spiral galaxy can suggest movement and focus, while an elliptical galaxy can offer a calmer and more concentrated field of light. An irregular galaxy can break symmetry and produce a wilder or less predictable sense of composition.

This diversity is valuable for design because it shows that the word “galaxy” does not refer to one single image. Not every cosmic composition needs to rely on the same spiral form. Planets, star clusters, regions of gas and different galactic structures can all carry very different atmospheres.

It is also possible to draw inspiration from the logic of real structures without copying scientific reality exactly. Spiral movement, concentrated centres, irregular distributions of light or the use of empty space can all become part of original graphic compositions.

Science does not narrow the possibilities available to design.

On the contrary, it expands the visual possibilities we can work with.

Does the Power of Galaxies Come Only From Their Beauty?

When we look at galaxy images, we often describe them as beautiful. Bright stars, colourful regions of gas and vast spiral arms make that reaction easy to understand. Yet the reason galaxies affect us may go beyond their visual appearance.

When we look at a galaxy, we also begin to think about scale. We know that billions of stars exist within the same system, even though most of them cannot be distinguished as individual points of light in the image. Even a small section of one spiral arm can contain countless stellar systems.

That knowledge changes the way we experience the image. A galaxy that begins as a beautiful form becomes something far beyond human scale once we consider its true size.

Perhaps this is exactly where the visual power of galaxies becomes strongest.

Our eyes see a shape.