3 Galaxies and Their Evolution Free Online FlashCards

What is a galaxy?

A galaxy is a gravitationally bound system of stars, gas, dust, stellar remnants, and dark matter.

What are key features of a spiral galaxy?

A spiral galaxy has a rotating, flattened disk, often with spiral arms and a central bulge. Many young stars form in its gas- and dust-rich arms.

How does a galaxy’s dark-matter halo affect it?

A dark-matter halo extends beyond a galaxy’s visible stars. Dark matter does not emit or reflect detectable light, but its gravity affects the motion of stars and gas.

How does gas help sustain a galaxy’s stellar life cycle?

Cold gas can collapse under gravity to form stars. Stars later return some material to space, enriching surrounding gas with elements made inside stars.

How did early galaxies begin to form?

Gravity gathered dark matter into halos; ordinary gas collected inside them, cooled, and formed stars. Small systems could then grow by drawing in gas and merging.

What can a close gravitational encounter do to a galaxy?

Close gravitational encounters can distort galaxies, pull out streams of stars and gas, or compress gas clouds and trigger a burst of star formation.

What is galactic cannibalism?

A large galaxy can gradually absorb smaller companions, adding their stars and gas to its own. This process is sometimes called galactic cannibalism.

What is the cosmic web?

The cosmic web is the large-scale pattern of filaments, walls, and sheets that contain groups and clusters of galaxies, with vast, relatively empty voids between them.

How can a galaxy’s environment influence its evolution?

A galaxy’s environment can affect its evolution: close neighbors make encounters and mergers more likely, while hot gas in a dense cluster can affect its gas supply.

How do elliptical galaxies differ from gas-rich spirals?

Elliptical galaxies range from nearly round to elongated. Their stars move in many directions, and they generally have less cold gas and less star formation than gas-rich spirals.

What distinguishes a lenticular galaxy?

A lenticular galaxy has a disk and central bulge but lacks prominent spiral arms. It often has little ongoing star formation.

What defines an irregular galaxy?

An irregular galaxy lacks a clear spiral or elliptical shape. Some are gas-rich, and some have been distorted by gravitational encounters.