Milky Way Galaxy – Key Concepts Review

30 question-and-answer flashcards covering major concepts, structures, historical discoveries, and future evolution of the Milky Way Galaxy, based on the lecture’s image captions and notes.

What celestial structure is our home galaxy and is prominently visible as a luminous band across the night sky?

The Milky Way Galaxy

Which siblings mapped star counts in different directions and produced the first cross-section diagram of the Milky Way?

William Herschel and Caroline Herschel

According to Harlow Shapley’s globular-cluster study, where is the Sun located relative to the Milky Way’s center?

Far from the center, about 25,000–28,000 light-years away

What overall structural type best describes the Milky Way: unbarred spiral, barred spiral, or elliptical?

A barred spiral galaxy

Name the four major components of the Milky Way highlighted in schematic diagrams (bulge, , halo, thin disk).

Thick disk

Which minor spiral arm contains our Sun?

The Orion Spur (also called the Orion–Cygnus Spur)

Why do astronomers use infrared surveys like 2MASS to study the Galactic bulge?

Infrared light penetrates interstellar dust better than visible light, revealing stars otherwise obscured

What feature at the Milky Way’s center is designated Sagittarius A*?

A compact radio/X-ray source believed to be a supermassive black hole

Approximately how massive is the black hole at the Galactic center as inferred from stellar orbits?

About 4 million solar masses

Which astronomer’s long-term infrared observations of stellar orbits provided strong evidence for the Galactic center black hole?

Andrea Ghez (and her team)

Describe the orbital motions of stars in the thin disk versus those in the halo.

Thin-disk stars follow nearly circular, co-planar orbits; halo stars have randomly oriented, highly elliptical orbits

What does the Galaxy’s ‘flat’ rotation curve (constant high speed at large radii) imply about its mass distribution?

Large amounts of unseen mass (dark matter) extend beyond the visible disk

What two main spiral arms emerge from the Milky Way’s central bar?

The Scutum-Centaurus Arm and the Perseus Arm

Which model proposes that the Milky Way formed from a single, rotating gas cloud that collapsed under gravity?

The monolithic collapse model

How do tidal streams in the Galactic halo form?

By the Milky Way shredding and absorbing smaller dwarf galaxies, leaving their stars in elongated streams

Name the dwarf galaxy currently being cannibalized by the Milky Way and located on the far side of the Galactic center.

The Sagittarius Dwarf Galaxy

What Hubble image (M54) is now thought to be the nucleus of the Sagittarius Dwarf Galaxy?

Globular cluster M54

In roughly how many billion years will the Milky Way begin a major collision with the Andromeda Galaxy?

About 3–4 billion years

After the Milky Way–Andromeda collision sequence, what type of galaxy is expected to form?

A large elliptical galaxy

What observational evidence distinguishes barred from unbarred spiral galaxies?

A central linear bar of stars with spiral arms emerging from its ends

Which survey mapped half a billion stars in infrared light, revealing the Galaxy’s bulge and thin disk?

The Two Micron All Sky Survey (2MASS)

Why would simple differential rotation alone eventually erase spiral arms?

Inner regions orbit faster than outer ones, winding arms tighter until they disappear, so other sustaining mechanisms are needed

What gaseous molecules (CO and H I) are commonly used to trace the Milky Way’s rotation curve?

Carbon monoxide (CO) and neutral hydrogen (H I)

Which mythological painting by Tintoretto illustrates a Greek legend explaining the Milky Way’s origin?

‘Origin of the Milky Way’

What star-forming regions near the Galactic center are labeled Sagittarius B1 and B2 in radio maps?

Giant molecular clouds experiencing vigorous star formation

How far is one kiloparsec in light-years, a unit often used on rotation-curve graphs?

1 kpc ≈ 3,260 light-years

What is the primary observable difference between the bulge and spiral arms in composite images?

The bulge is dominated by old, yellow-red stars; the arms show young, blue stars and glowing gas

Which neighboring spiral galaxy (M31) provides an external view of a system similar to the Milky Way?

The Andromeda Galaxy

How do thick-disk stars differ chemically from thin-disk stars?

Thick-disk stars are generally older and have lower metallicity (fewer heavy elements)

What term describes the long, threadlike radio features seen near the Galactic center?

Radio filaments