Slide 1
An elliptical galaxy’s smooth glow hides varied orbits
Elliptical galaxies appear as smooth rounded or elongated distributions of starlight. Their stars do not all follow one thin, orderly disk.
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The name describes the projected outline seen on the sky. A two-dimensional appearance cannot uniquely reveal the galaxy’s full three-dimensional shape or the detailed paths of its stars.
Slide 2
Stars move in many directions rather than one thin disk
Stars in an elliptical galaxy can follow orbits in varied directions. Their motions contribute to maintaining an extended stellar distribution against gravity.
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Random motion here means a spread of orbital directions, not an absence of gravitational rules. Each star still responds to the overall gravitational field of the galaxy.
Slide 3
Older stars often dominate over new star formation
Many elliptical galaxies contain mainly older stellar populations and relatively little cold gas for new star formation. Their appearance differs from bright spiral arms.
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A reddish integrated color can reflect the mix of stars rather than one uniform stellar temperature. A galaxy’s spectrum combines light from many stars and must be interpreted as a population.
Slide 4
Similar outlines can hide very different sizes and histories
Elliptical galaxies range from relatively small systems to enormous galaxies. A shared outline does not imply identical mass, environment or history.
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Classification is useful for organizing observations, but it compresses diversity. Comparing mass and stellar motions can reveal important differences between galaxies that look similar in a small image.
Slide 5
Shape alone cannot establish how a galaxy formed
Mergers and other evolutionary processes can contribute to elliptical galaxies. Shape alone does not establish one exact history for an individual system.
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Subtle structures and stellar populations may preserve evidence of earlier interactions. The challenge is to connect those traces with a history consistent with the present distribution and motion of stars.
Sources
- Types of Galaxies
OpenStax, Rice University
- Galaxy Types
NASA