Grade 12 Science: Galaxies

A complete set of practice flashcards covering galaxy definitions, sizes, classification systems, evolution, dark matter, supermassive black holes, observation wavelengths, and cosmic structures.

What is a galaxy?

A galaxy is a huge collection of stars, gas, plasma, dust, and dark matter that are held together by gravity.

How do dwarf galaxies compare to giant galaxies in terms of star count?

Small dwarf galaxies have millions of stars, while giant galaxies can have trillions of stars.

What three main shapes are used to categorize galaxies?

Spiral (shaped like a spinning disc with curved arms), Elliptical (round or oval shaped), and Irregular (does not have a clear or regular shape).

What classification system do scientists use to categorize galaxies by their shapes?

The Hubble Sequence.

How many galaxies exist in the observable universe according to current estimates?

There are at least hundreds of billions of galaxies in the observable universe, with some estimates reaching around 2 trillion.

How did galaxies initially begin forming in the early universe?

Galaxies began forming from small differences in the density of matter in the early universe.

Through what processes do galaxies change over time?

Galaxies change over time through star formation, collisions & mergers, and interactions with other galaxies.

How do scientists know dark matter exists despite it being invisible?

Scientists know dark matter is there because of the way its gravity affects stars and other matter, helping explain why stars in galaxies rotate at the speeds they do.

Where are supermassive black holes located in galaxies, and how massive are they?

They are located at the center of many galaxies and can contain millions or billions of times the mass of the Sun.

What creates an active galactic nucleus (AGN)?

An active galactic nucleus (AGN) is created when material falls toward a supermassive black hole and releases enormous amounts of energy.

What types of light wavelengths do scientists observe to study galaxies?

Visible light, Infrared, Radio waves, Ultra violet, and X-rays.

What hierarchy describes how galaxies gather into larger structures in the cosmic web?

Galaxies -> Groups -> Clusters -> Cosmic web.

What are the huge empty regions between galactic sheets and filaments called?

Voids.

Where does the word galaxy originate from and what does it mean?

It comes from the Greek word galaxias, meaning milky circle, derived from the appearance of the Milky Way in the night sky.

What does the word Galaxy with a capital G specifically refer to?

It is sometimes used to specifically mean our own galaxy, the Milky Way.

Why were other galaxies long ago called island universes?

Because scientists thought of them as separate systems similar to our own Milky Way.