08 The Milky Way Galaxy Free Online FlashCards

What defines the Milky Way as a barred spiral galaxy?

It is a rotating galaxy with a central bar and spiral arms.

How long does the Sun take to orbit the galactic center?

The Sun takes roughly 240 million years to complete one orbit around the galactic center.

What makes up the interstellar medium?

The interstellar medium is mostly gas, with tiny solid dust grains. Its gas occurs in hot ionized, warmer atomic, and cold molecular conditions.

How does interstellar dust affect visible light?

Dust absorbs and scatters visible light, making distant parts of the Galaxy harder to see and reddening the light that reaches us.

What are the main characteristics of open clusters?

Open clusters are relatively loose groups, usually in the disk and often near spiral arms. They contain tens to thousands of stars and can gradually disperse as they orbit.

How do outer-galaxy rotation speeds support dark matter?

In many spiral galaxies, outer stars and gas move faster than visible matter alone predicts; their speeds remain roughly level instead of dropping. This supports an extended dark-matter halo inferred from gravity.

Where is the Sun located in the Milky Way?

The disk is a broad, flattened region containing most of the Milky Way’s stars, gas, and dust. The Sun lies about halfway from the center in the Orion Spur.

How do the thin and thick disks differ?

The thin disk includes many young stars and active star-forming regions; the older, thicker disk extends farther above and below the galactic plane.

What lies at the center of the Milky Way?

The central bar and bulge are dense regions containing many older stars. Sagittarius A*, a supermassive black hole, lies at the very center.

What is the stellar halo?

The stellar halo is a sparse, roughly spherical region surrounding the disk and bulge; it contains old stars and many globular clusters.

What is the Milky Way’s dark-matter halo?

It is an unseen mass distribution inferred from gravity that extends beyond the regions containing most of the Galaxy’s visible stars.

How can molecular clouds lead to star formation?

Gravity can cause parts of molecular clouds to collapse, forming new stars.