AST 112 - Chapter 25 - Week 6

Spring 2025

What is the hazy trail of light that stretches across the sky in remote, dark areas?

The Milky Way galaxy

How many galaxies are there in the observable universe?

Roughly 100 billion

Where is the Milky Way located in the universe?

In a galaxy group on the outskirts of the Virgo supercluster

What is one reason why it is difficult to directly image our own Milky Way galaxy?

Because we reside inside of it, making it challenging to get an external perspective

What component of our Milky Way galaxy contains younger stars?

The thin disk

What describes the structure of a galaxy, including the Milky Way?

They are not solid structures; individual stars follow their own orbital paths around the center

What motion do stars in the flattened disk of the Milky Way exhibit?

A bobbing up and down motion as they orbit around the center of the galaxy

How much time does it take for the Sun to complete one orbit around our galactic center, also known as a galactic year?

Approximately 200 million years

What does the flat rotation curve of the Milky Way suggest about the distribution of its mass?

That most of the mass lies beyond visible stars and suggests a large amount of dark matter

What is dark matter?

It is an undetected form of mass that does not interact with light

What is the distance from the Earth to the center of the Milky Way galaxy?

26,000 light years

What object is at the very center of the Milky Way galaxy?

Sagittarius A

What does SNR stand for in the context of radio images of the galaxy?

Supernova Remnant

What isn’t visible in the X-ray images of the galaxy?

Gas giants

According to Kepler’s Law, what does the rapid orbit of stars around an unseen object at the very center of the Milky Way suggest about the mass of the invisible object?

It has to be millions of times the mass of our sun

What is the primary role of galaxies in the universe?

To act like cosmic recycling plants where material from dead stars is reused

Where were the heavier elements beyond hydrogen and helium created?

In the depths of massive stars and their supernova explosions

What is the significance of galactic recycling for our Solar System?

It makes the formation of rocky planets like Earth possible

What distinguishes Population II stars from Population I stars?

Population II stars are older, and have a smaller proportion of heavy elements

Why do new stars currently form in the disk of the Milky Way, but not out in the Halo?

The halo lacks cold, dense gas that is necessary for star formation