Astro 150 S 2024 Final Review 2/2 May 3, 2024

What happens immediately after a solar-mass main sequence star stops burning hydrogen fuel in its core?

• Helium fuses in the core

• Helium flash

• Hydrogen fuses in shells around the core

• The core compresses

Tags

NGSS.HS-ESS1-1

Supernova explosions will result in... (multiple correct answers)

• White dwarfs

• Neutron stars

• Black holes

• Complete destruction of the star

Answer explanation

Only those stars greater than about 8 solar masses detonate in supernova explosions. Stars above this mass also will become either neutron stars or black holes.

Tags

NGSS.HS-ESS1-3

Which of these is NOT a way we can detect black holes?

• Direct imaging

• Radiation from accretion disks

• Watching objects disappear into them

From the point of view of an astronaut falling into a black hole, how is time passing for things far away from the black hole?

• Time is flowing the same

• Time is speeding up

• Time is slowing down

• It depends on the black hole mass

Answer explanation

Due to the extreme gravity near a black hole, time slows way down for things close to the black hole (from the perspective of an outside observer). For an observer close to the black hole, it looks like everything else is sped up.

What makes the 21 cm line?

• A certain hydrogen spectral line

• A certain helium spectral line

• Hydrogen electrons flipping spin

• Helium electrons flipping spin

Answer explanation

When a hydrogen's electron flips its spin, it releases a photon with a 21 cm wavelength.

Tags

NGSS.HS-PS4-3

Why does the Milky Way's rotation curve look like this?

• The stars orbit according to Kepler's laws

• There is a lot of dark matter in our Galaxy

• Gravitational interactions between stars speed up orbits

• This actually ISN'T the rotation curve we observe

Answer explanation

If most of the mass of the Galaxy were contained at the center, the Milky Way's rotation would follow a Keplerian orbit--material on the outside would orbit more slowly. The reason that the orbital speed doesn't change much as you go farther out is because the mass is more evenly distributed, thanks to dark matter.

Tags

NGSS.HS-PS2-4

What type of galaxy is the Milky Way?

• An elliptical

• A spiral

• A barred spiral

• An irregular

Where do giant elliptical galaxies come from?

• Spiral galaxies using up all their material

• They form from enormous gas clouds

• Ordinary ellipticals stripping matter from passing galaxies

• Spiral galaxies merging together

Answer explanation

As spiral galaxies collide, their gas clouds collide and trigger bursts of star formation. The galaxies combine, and once the new stars die out, the resulting galaxy is very large (hence, giant elliptical) and very yellow because there are only longer-lived, less blue stars there.

Why do galaxies collide, but stars don't?

• Gravitational interaction swings stars away from each other

• There is a lot of space between the stars compared to their size

• Most stars get flung away from each other during galactic collisions

• They do, they just become black holes and disappear on collision

Answer explanation

The stars are extremely far apart for their size. The size-distance difference is analogous to having two grapefruits with one in New York and the other in San Francisco.

Tags

NGSS.HS-PS2-4

What differentiates the different types of AGN?

• Their inclination toward us

• Their distance away from us

• Their age

• Their mass