Describe how elliptical galaxies and spiral bulges are similar.

Elliptical galaxies and spiral bulges are rich in older stars. These stars, often billions of years old, typically have a reddish hue. This happens because older stars burn cooler and emit light at a longer wavelength. Both these structures have a minimal amount of ongoing star formation.

Consequently, they share similar characteristics when it comes to age and color. These older stars have already exhausted much of their hydrogen fuel and have entered later stages of evolution, becoming giants or even remnants, like white dwarfs.

Because these regions have little to no gas and dust, which are necessary elements for new star formation, the stellar population remains relatively static over time.

The motion of stars in elliptical galaxies and spiral bulges is mostly random. Unlike spiral arms, where stars move along well-defined orbits, here stars exhibit more chaotic, non-circular motions.

This randomness is what contributes to the smooth, featureless appearance of these structures. From a dynamics perspective, the stars within both enjoy a balanced gravitational pull that prevents any significant disruption in their collective orbits.

This non-rotational star motion is one of the key reasons these systems lack the distinct spiral arms found in other types of galaxies. Without a concerted rotational force, the stars distribute themselves more evenly, leading to a spherical or ellipsoidal shape.

The stability of elliptical galaxies and spiral bulges is largely due to their strong gravitational influence. The combined gravitational force from all the stars in these structures ensures that they maintain their shape without major disturbances.

Each star contributes to a collective gravitational pull, effectively keeping the system cohesive and preventing individual stars from straying too far from their positions.

This balanced force is crucial for maintaining equilibrium within the galaxy or bulge, as it promotes a stable environment where the stars move according to the overall gravitational field, which remains consistent over long periods.