Question 1

What objects are used to determine that the galaxy is mostly dark matter?

Accepted Answer

The presence of dark matter is indicated

Question 2

Magnetic fields in the Milky Way are concentrated in the disk because:

Accepted Answer

A) halo stars are incapable of producing strong magnetic fields 
B) the fields are tied to the charged particles in dense molecular clouds 
C) gravity forces them to sink to the center of the disk 
D) supernovae explosions continually force them toward the middle of the disk 
E) supernovae explosions eliminate magnetic fields away from the disk 
A) halo stars are incapable of producing strong magnetic fields 
B) the fields are tied to the charged particles in dense molecular clouds 
C) gravity forces them to sink to the center of the disk 
D) supernovae explosions continually force them toward the middle of the disk 
E) supernovae explosions eliminate magnetic fields away from the disk

Question 3

Cosmic rays come mostly from extragalactic sources and contribute little to the overall energy balance in the Milky Way disk.

Accepted Answer

A) True 
 B)False

Question 4

Suppose it was discovered that the galaxy has constantly been absorbing large amounts of gas that never had any stars form in it.Would this complicate our interpretation of ages and chemical enrichment?

Accepted Answer

Such a discovery might indeed complicate

Question 5

Our galaxy is classified as an Sd galaxy in the Hubble sequence.

Accepted Answer

A) True 
 B)False

Question 6

What are the main observational difficulties in observing the shape and spiral arm pattern of the Milky Way?

Accepted Answer

We are seeing it from within,s

Question 7

In which part of the Milky Way would you find little or no neutral hydrogen,no current star formation,and stars that are all older than 10 billion years?

Accepted Answer

A) the inner disk 
B) the outer disk 
C) the galactic center 
D) the solar neighborhood 
E) the halo 
A) the inner disk 
B) the outer disk 
C) the galactic center 
D) the solar neighborhood 
E) the halo

Question 8

Stars in the halo are most easily identified passing by the Sun because of their distinctively redder colors.

Accepted Answer

A) True 
 B)False

Question 9

Calculate the size of the event horizon of the supermassive black hole at the center of the Milky Way,the mass of which is 4 × 106 M⨀.Give your answer in units of AU.

Accepted Answer

R_s = 2GM/c² = 2 × 6.7 × 10⁻¹¹ m³/kg

Question 10

There is a 109 M⨀ black hole at the center of the Milky Way that is rapidly accreting stars and gas.

Accepted Answer

A) True 
 B)False

Question 11

If a globular cluster were 1,000 pc away from us and an RR Lyrae star in it had an absolute magnitude of 0.5,what would its apparent magnitude be?

Accepted Answer

A) 4.0 
B) 6.5 
C) 8.0 
D) 10.5 
E) 15.5 
A) 4.0 
B) 6.5 
C) 8.0 
D) 10.5 
E) 15.5

Question 12

Why is 21-cm radiation the best way to map the spiral arms in the Milky Way?

Accepted Answer

A) The molecular hydrogen gas that produces this emission is concentrated in the spiral arms. 
B) These photons,which are produced by neutral hydrogen,pass through the dense clouds of gas and dust in the disk. 
C) The emission is produced by supernovae,which are concentrated in the spiral arms. 
D) Radio telescopes are easier to operate than optical telescopes,and observations can be made even during the daytime. 
E) Radio photons do not have Doppler shifts,so we can detect clouds of gas without having to worry about the orbital velocities. 
A) The molecular hydrogen gas that produces this emission is concentrated in the spiral arms. 
B) These photons,which are produced by neutral hydrogen,pass through the dense clouds of gas and dust in the disk. 
C) The emission is produced by supernovae,which are concentrated in the spiral arms. 
D) Radio telescopes are easier to operate than optical telescopes,and observations can be made even during the daytime. 
E) Radio photons do not have Doppler shifts,so we can detect clouds of gas without having to worry about the orbital velocities.

Question 13

The Milky Way has two major spiral arms that emanate from the ends of its bar.

Accepted Answer

A) True 
 B)False

Question 14

If you found a halo star that was 13 billion years old and had the same amount of heavy elements as the Sun,would you be surprised?

Accepted Answer

A) No;many halo stars have high fractions of heavy elements. 
B) No;this star probably escaped from a globular cluster. 
C) No;this star has been around a long time,and has created a lot of heavy elements through nuclear fusion. 
D) Yes,because most halo or globular cluster stars have few heavy elements. 
E) Yes;halo stars mostly have ages less than 10 billion years. 
A) No;many halo stars have high fractions of heavy elements. 
B) No;this star probably escaped from a globular cluster. 
C) No;this star has been around a long time,and has created a lot of heavy elements through nuclear fusion. 
D) Yes,because most halo or globular cluster stars have few heavy elements. 
E) Yes;halo stars mostly have ages less than 10 billion years.

Question 15

If we found a star cluster at the edge of the disk of the Milky Way at a distance of 10 kpc from the center,which orbited with a velocity of 300 km/s,what would be the total mass enclosed within this radius?

Accepted Answer

A) 3 × 1011 M⨀ 
B) 7 × 1011 MV 
C) 2 × 1011 M⨀ 
D) 4 × 1012 M⨀ 
E) 8 × 1012 M⨀ 
A) 3 × 1011 M⨀ 
B) 7 × 1011 MV 
C) 2 × 1011 M⨀ 
D) 4 × 1012 M⨀ 
E) 8 × 1012 M⨀

Question 16

Why can the observed chemical abundance of a star tell you something about its age?

Accepted Answer

As a galaxy evolves,gas is converted to

Question 17

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

Accepted Answer

A) one single cloud of gas gently collapsing and star formation proceeding slowly within it 
B) one single cloud of gas that rapidly collapsed and turned most of its gas into stars 
C) violent merging of protogalactic fragments that stimulated a high rate of star formation 
D) slow merging of protogalactic fragments after they had already turned most of their gas into stars 
E) merging of two galaxies,each about half as massive as the Milky Way is today 
A) one single cloud of gas gently collapsing and star formation proceeding slowly within it 
B) one single cloud of gas that rapidly collapsed and turned most of its gas into stars 
C) violent merging of protogalactic fragments that stimulated a high rate of star formation 
D) slow merging of protogalactic fragments after they had already turned most of their gas into stars 
E) merging of two galaxies,each about half as massive as the Milky Way is today

Question 18

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had:

Accepted Answer

A) not yet formed stars 
B) converted most of their gas into stars 
C) begun forming stars 
D) each formed a supermassive black hole at their center 
E) gathered a lot of dark matter from surrounding space 
A) not yet formed stars 
B) converted most of their gas into stars 
C) begun forming stars 
D) each formed a supermassive black hole at their center 
E) gathered a lot of dark matter from surrounding space

Question 19

How many years does it take the Sun to complete one orbit around the Milky Way? Note that the Sun is traveling at approximately 220 km/s and is 8 kpc from the center of the Milky Way.

Accepted Answer

A) 180 thousand years 
B) 7 million years 
C) 35 million years 
D) 230 million years 
E) 620 million years 
A) 180 thousand years 
B) 7 million years 
C) 35 million years 
D) 230 million years 
E) 620 million years

Question 20

Stars in the Milky Way that are 12 to 13 billion years old are only found in globular clusters.

Accepted Answer

A) True 
 B)False

Exam 21: The Milky Waya Normal Spiral Galaxy

What objects are used to determine that the galaxy is mostly dark matter?

Magnetic fields in the Milky Way are concentrated in the disk because:

Cosmic rays come mostly from extragalactic sources and contribute little to the overall energy balance in the Milky Way disk.

Suppose it was discovered that the galaxy has constantly been absorbing large amounts of gas that never had any stars form in it.Would this complicate our interpretation of ages and chemical enrichment?

Our galaxy is classified as an Sd galaxy in the Hubble sequence.

What are the main observational difficulties in observing the shape and spiral arm pattern of the Milky Way?

In which part of the Milky Way would you find little or no neutral hydrogen,no current star formation,and stars that are all older than 10 billion years?

Stars in the halo are most easily identified passing by the Sun because of their distinctively redder colors.

Calculate the size of the event horizon of the supermassive black hole at the center of the Milky Way,the mass of which is 4 × 106 M⨀.Give your answer in units of AU.

There is a 109 M⨀ black hole at the center of the Milky Way that is rapidly accreting stars and gas.

If a globular cluster were 1,000 pc away from us and an RR Lyrae star in it had an absolute magnitude of 0.5,what would its apparent magnitude be?

Why is 21-cm radiation the best way to map the spiral arms in the Milky Way?

The Milky Way has two major spiral arms that emanate from the ends of its bar.

If you found a halo star that was 13 billion years old and had the same amount of heavy elements as the Sun,would you be surprised?

If we found a star cluster at the edge of the disk of the Milky Way at a distance of 10 kpc from the center,which orbited with a velocity of 300 km/s,what would be the total mass enclosed within this radius?

Why can the observed chemical abundance of a star tell you something about its age?

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had:

How many years does it take the Sun to complete one orbit around the Milky Way? Note that the Sun is traveling at approximately 220 km/s and is 8 kpc from the center of the Milky Way.

Stars in the Milky Way that are 12 to 13 billion years old are only found in globular clusters.

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornments Moons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

The Expanding Universe

Galaxies

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

Calculate the size of the event horizon of the supermassive black hole at the center of the Milky Way,the mass of which is 4 × 10⁶ M_⨀.Give your answer in units of AU.

There is a 10⁹ M_⨀ black hole at the center of the Milky Way that is rapidly accreting stars and gas.