AStronomy final

The Milky Way has different populations of stars; the has the oldest stars in a large sphere of
randomly-tilted orbits while the has the youngest stars all orbiting in a plane.

halo; nucleus

How did we first learn the Sun is not at the center of the Milky Way?

by mapping the location of
globular clusters on the sky

Over time the slight amounts of heavier elements in the Milky Way’s gas increase due to

stars forging heavier elements and spreading them when they die

How much of the Milky Way’s total mass is dark matter?

90 percent

In the Milky Way, where do stars usually form?

in the spiral arms of the disk

What are the Milky Way’s spiral arms?

regions of higher density where gas compresses and forms
new stars

Why are high-mass stars only in spiral arms while low-mass stars are everywhere?

high-mass stars
die before leaving the arms but low-mass stars live long enough to drift away

Which lists the order in which the stars of our galaxy formed?

nucleus and halo first, then disk, then
spiral arms

As generations of stars are born and die, what do they do to the rest of the gas in a galaxy?

increase
the metallicity of the gas

A red dwarf just born in a spiral arm would have a red dwarf born billions of years ago in the
nucleus.

higher metallicity

Which galaxy component contains young and old stars, gas, and dust all orbiting in the same plane and
direction?

the disk

Which galaxy component contains invisible mass whose gravity affects orbital speeds?

the dark
matter halo

Which galaxy component contains old stars with tilted orbits and globular clusters?

the stellar halo

Which galaxy component contains old stars with tilted orbits and the Milky Way’s central black hole?

the nucleus

For a spiral galaxy, where are the low-metallicity low-mass stars found?

in the halo

Which galaxy type forms the fewest stars?

elliptical galaxies

What launches the narrow jets in some galaxies detected at radio wavelengths?

a supermassive
black hole’s accretion disk

How do astronomers determine whether something is a small galaxy or a star cluster?

by seeing
whether more mass is required than the stars alone provide

How do astronomers measure the total mass of a galaxy?

by observing orbital motions of stars and
gas

Large elliptical galaxies today formed mostly through what process?

major mergers in massive dark
matter halos

Medium-mass halos that grew slowly and avoided major mergers became what kind of galaxies?

spiral galaxies

Small halos heated by the first stars in larger galaxies became what kind of galaxies?

dwarf irregular
galaxies

Which distance method is used for a nearby star vs. a distant quasar?

parallax for stars; Hubble’s law
for quasars

If light from a galaxy took 10 million years to reach us, how do we see it?

as it was 10 million years
ago

If galaxy light traveled 10 billion years, how far has it likely traveled?

more than 10 billion light years

Which observation helps us learn about the first galaxies?

observing very high-redshift galaxies

Why doesn’t the expansion of the universe pull galaxy clusters apart?

their gravity holds them
together

Between which objects would the expansion of space be greatest?

between the Milky Way and a
distant galaxy

What observations reveal the expansion history of the universe?

supernova brightnesses and
redshifts

What is the theoretical limit to how far we could see without expansion?

about 14 billion light years

What explains why galaxies and clusters contain mass we cannot see?

dark matter

What explains the accelerating expansion of the universe?

dark energy

What explains the universe’s age, composition, and background radiation?

the Big Bang

What test did the Big Bang pass?

predicting the abundance of light elements

What do astronomers know happened before the Big Bang?

nothing is known about what came
before it

How old is the universe?

about 14 billion years

What determines the ultimate fate of the universe?

the balance of gravity and dark energy