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Types of Galaxies: A Complete Overview

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  1. Spiral galaxies

    Spiral galaxies are disk-shaped, with spiral arms winding outward from a bright central bulge. Our own Milky Way and its closest large neighbor, the Andromeda Galaxy, are both spirals. Their arms are rich in young, hot stars, gas, and dust, making them active sites of new star formation.

  2. Elliptical galaxies

    Elliptical galaxies lack spiral arms or a distinct disk, ranging in shape from nearly spherical to flattened ovals. They're generally made of older, redder stars with little new star formation. Some of the largest elliptical galaxies form from repeated collisions and mergers at the centers of galaxy clusters.

  3. Irregular galaxies

    Irregular galaxies have no clear, symmetric shape like spirals or ellipticals, often because collisions or gravitational interactions with other galaxies have disrupted their structure. The Large and Small Magellanic Clouds, satellite galaxies of the Milky Way, are classic examples.

  4. Hubble's galaxy classification

    Around 1926, astronomer Edwin Hubble grouped galaxies by shape into ellipticals (E0-E7), lenticulars (S0), spirals (Sa, Sb, Sc), and barred spirals (SBa, SBb, SBc), arranging them into a tuning-fork-shaped diagram. This "Hubble tuning fork" is still widely used as the basic framework for classifying galaxy shapes today.

  5. Barred spiral galaxies

    A barred spiral galaxy is a spiral with a straight, bar-shaped structure of stars crossing its center, with spiral arms extending from either end of the bar. The Milky Way itself is classified as a barred spiral, and a large share of all spiral galaxies are believed to have this bar structure.

  6. Where the solar system sits in the Milky Way

    Within the roughly 100,000-light-year-wide Milky Way, the solar system isn't at the center β€” it sits in the Orion Arm (a minor spiral arm), about 26,000 light-years out toward the galaxy's edge. The solar system takes roughly 230 million years to complete one orbit around the galactic center.

What is a galaxy?

A galaxy is a massive collection of hundreds of millions to hundreds of billions of stars, gas, dust, and dark matter, all bound together by gravity. The observable universe is estimated to contain hundreds of billions of galaxies, each classifiable into a handful of shape categories.

Galaxies are still moving apart from each other

The fact that the distances between galaxies keep growing over time is key evidence that the universe is expanding. Understanding that expansion is a natural next step after learning about galaxy types.

Frequently Asked Questions

When will the Andromeda Galaxy collide with the Milky Way?

Andromeda is approaching the Milky Way at roughly 110 km/s, and scientists predict the two galaxies will collide and merge in about 4 billion years. Because the distances between individual stars are so vast, actual star-to-star collisions are extremely unlikely even then.

Does every galaxy fit clearly into one shape category?

No. Some galaxies, like lenticular (S0) galaxies, sit in between spiral and elliptical shapes and don't fit neatly into Hubble's classification, meaning real galaxy shapes are far more varied than the classification system suggests.