Elliptical vs Spiral Galaxies: Stellar Differences Explained

Let's embark on a cosmic journey, setting our sights on two distinct galaxies - the spiral NGC 4647 and elliptical M60. Nestled 54 million and 63 million light-years away from Earth respectively, these two galaxies serendipitously align almost perfectly in our line of sight. This alignment, immortalized in a Hubble image, provides a unique opportunity to delve into the contrasting characteristics of these galaxy types.

Starting with their architecture, elliptical galaxies, like M60, exhibit an ellipsoid form, their stars evenly scattered but denser at the core. Spiral galaxies, such as NGC 4647, present a slightly more intricate design. They possess an ellipsoid-shaped nucleus, enveloped by an exceedingly thin disk, which is the birthplace of their distinctive spiral arms.

A second and visually striking difference lies in their color palette. Spiral galaxies paint the cosmos in hues of blue, whereas elliptical galaxies appear more whitish. These color variations hint at the age and composition of the stars within. Elliptical galaxies are home to older, yellow-hued stars, while spiral galaxies host a younger generation of stars, their intense heat and mass radiating a vibrant blue. However, the heart of spiral galaxies is older, yielding a whitish appearance.

This color divergence also underscores the varying amount of interstellar gas within these galaxies. Elliptical galaxies, like M60, are virtually barren of this gas, devoid of the raw materials needed for star creation. Contrastingly, spiral galaxies, such as NGC 4647, are teeming with gas and dust, providing the perfect nursery for continual star birth.

Image Credit: NASA, ESA, Hubble Heritage Team (STScI/AURA).