The cosmic evolution from rotating pinwheels to smooth ovals

Space · Published 25 October 2026 Swipe more like this →

In short: Galaxies are not just static collections of stars; they are dynamic structures that evolve through collisions and maturation. From the barred spirals we call home to the gas-poor ellipticals born of violent mergers, the diversity of galactic shapes reveals a history of celestial interaction.

Astronomers primarily categorize galaxies by their physical shapes and the activity occurring in their central regions—often powered by supermassive black holes. Spiral galaxies, such as our Milky Way and Andromeda, are characterized by pancake-like disks with rotating arms where young stars form from gas. These systems are often surrounded by halos containing old stars, star clusters, and dark matter, which exerts a gravitational pull without emitting light. Some spiral arms appear loosely wound while others are tight. Certain spirals remain hidden from our view because they are oriented edge-on.

A significant subtype is the barred spiral, which features ribbons of gas and dust cutting across the center. Scientists believe these bars indicate that a galaxy has reached full maturity. In contrast, elliptical galaxies range from round to oval shapes with very little organization. Because they contain minimal gas and dust, they lack new star formation; instead, their older stars orbit the core in random directions. These are thought to originate from collisions and mergers between spiral galaxies. Elliptical galaxies are less common than their spiral counterparts. These oval structures show very little internal organization or structure.

Lenticular galaxies serve as a structural middle ground, possessing the central bulge and disk of spirals but lacking the arms. They share the older stellar populations of ellipticals, leading to theories that they may be faded spirals or products of mergers. Finally, irregular galaxies—ranging from dwarf types with 100 million times the Sun’s mass to giants weighing 10 billion solar masses—exhibit chaotic shapes like rings or toothpicks, often caused by gravitational interactions with neighboring galaxies. These irregular shapes can resemble toothpicks or small groupings of stars. Some dwarf irregulars possess only 100 million times the mass of our Sun.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• The structural backbone of the cosmos is defined by gravity and shape
• Galaxies are the visible foundation of the universe, but how do they evolve?
• A spiral galaxy's arms are traffic jams that stars drive through
• Why do some galaxies display such perfect, sweeping, and majestic spiral arms?
• Galaxies that exist in the vast emptiness of cosmic voids
• The cosmic mystery of galaxies being stripped of their building blocks
• The mysterious forces pulling our galaxy toward the unknown
• The Milky Way is a 100,000 light-year wide cosmic theater
• The universe contains trillions of galaxies, each a cosmic city
• What defines a galaxy in the vast expanse of space?
• The distant galaxy that might have revealed the universe's first stars
• From tiny clusters to cosmic webs, galaxies define our universe

More in Galaxies · More in Space · Latest · A–Z · All topics