Astronomy
The Relationship Between Galaxy Morphology and Star Formation
Quick fact
Around 70% of all stars in the universe are born in spiral galaxies, even though spirals make up only about 20% of all galaxies.
Why this is interesting
You've seen images of beautiful spiral galaxies and round, smooth elliptical galaxies—but did you know their shapes reveal whether they are actively giving birth to new stars or are largely dormant?
Read the full explanation
Understanding The Relationship Between Galaxy Morphology and Star Formation
Galaxies come in three main shapes: spiral (like our Milky Way), elliptical (round and smooth), and irregular (chaotic). These shapes, called morphologies, are not just aesthetic—they tell us how much gas is available for star formation. Spiral galaxies have cold, dense gas clouds in their arms, which collapse to form new stars. Elliptical galaxies, in contrast, have little gas left; most of it was used up long ago or stripped away, so they form stars very slowly or not at all. Irregular galaxies often have plenty of gas and show bursts of star formation, especially if they have recently interacted with another galaxy. In short, a galaxy's morphology is a snapshot of its star-forming potential.
A deeper explanation
The relationship stems from galactic dynamics and evolution. Spirals maintain their gas reservoirs through a steady supply from the cosmic web and internal recycling, allowing continuous star formation. Ellipticals are thought to result from mergers of gas-rich galaxies that funnel gas to the center, triggering a starburst that consumes the fuel, leaving a gas-poor, red-and-dead galaxy. Environment also plays a role: galaxies in dense clusters often have their gas stripped, transforming spirals into passive lenticulars or ellipticals. The star formation rate in a galaxy is thus intimately tied to its morphology, history, and surroundings. This correlation is a key diagnostic in extragalactic astronomy, allowing astronomers to estimate a galaxy's star formation activity just by its Hubble type, and to trace galaxy evolution over cosmic time.