Question 1

Which kind of active galaxies has been observed at the greatest distances from us
A)Seyfert galaxies
B)radio galaxies
C)quasars

Accepted Answer

Quasars have been observed at the greatest distances from us, some as far as 13 billion light years away. Seyfert galaxies and radio galaxies, while still relatively distant, have not been observed at such extreme distances.

Question 2

The diagram illustrates physical size and angular size as seen by the observer. We can estimate the size in light years (or parsecs or km) of M31 from 
A)its angular size in degrees.
B)its distance in light years (or parsecs or km).
C)its angular size in degrees and its distance in light years (or parsecs or km).
D)It is impossible to estimate the size of M31.

Accepted Answer

Using the diagram, we can measure the angular size of M31 to be approximately 3 degrees. To estimate the distance to M31, we can use the standard ruler method. By comparing the physical size of M31 (measured in the diagram) to its angular size (measured in degrees), we can calculate its distance. Assuming the physical size of M31 is 100,000 light years, we can set up a proportion:

Physical size / Distance = Angular size

Plugging in the values we have, we get:

100,000 ly / Distance = 3 degrees

Solving for distance, we get:

Distance = 100,000 ly / 3 degrees = 33,333 ly/degree

Multiplying this by the angular size of M31 (3 degrees), we get the distance to M31:

Distance = 33,333 ly/degree * 3 degrees = 100,000 ly

Therefore, the size of M31 can be estimated to be approximately 100,000 light years and its angular size is approximately 3 degrees.

Question 3

Why do astronomers believe supermassive black holes are the source of an AGN's energy
A)Such black holes have been found at the center of most galaxies, both active and inactive.
B)Radio jets are seen from low-mass black holes plus accretion disks inside our galaxy.
C)Jets and accretion disks have been observed in active galaxies.
D)Black holes can produce so much energy in such a small place.
E)All of the other choices are correct.

Accepted Answer

All of the choices are correct. Astronomers have observed supermassive black holes at the center of most galaxies, both active and inactive. They have also observed jets and accretion disks in the active galaxies, which are believed to be powered by the black holes. Additionally, low-mass black holes and accretion disks inside our own galaxy have been observed emitting radio jets. Lastly, black holes can produce enormous amounts of energy in a very small space, making them a likely source of the energy seen in AGNs.

Question 4

Recent high resolution radio observations show that quasars can be classified as
A)exploding supernova stars.
B)exploding planets.
C)normal galaxies like our Milky Way Galaxy.
D)a kind of active galaxy similar to Seyfert and radio galaxies.

Accepted Answer

The passage states that recent high resolution radio observations classify quasars as "a kind of active galaxy similar to Seyfert and radio galaxies." Therefore, the best choice is D.

Question 5

Astronomers who discovered quasars found that they show ___________ of their spectral lines and are thus probably much ___________ than nearby galaxies.
A)large redshifts; farther away
B)large blueshifts; farther away
C)no wavelength difference; nearer
D)large redshifts; nearer
E)large blueshift; nearer

Accepted Answer

Astronomers found that quasars show large redshifts in their spectral lines. This means that the wavelengths of light emitted by quasars are shifted towards longer, or redder, wavelengths. This is a result of the Doppler effect, which occurs when an object is moving away from us. The greater the redshift, the farther away the object is. Therefore, quasars are probably much farther away than nearby galaxies.

Question 6

Jet-shaped regions of radio and optical emission have been observed in
A)quasars.
B)radio galaxies.
C)the 3-Kelvin radiation.
D)quasars and radio galaxies.

Accepted Answer

Jet-shaped regions of radio and optical emission have been observed in both quasars and radio galaxies.

Question 7

How are astronomers able to determine that quasars are so small
A)They are variable over a short period of time.
B)They emit mainly X-rays.
C)They are only found at very large distance.
D)The structure of a quasar is completely resolved in images.

Accepted Answer

Astronomers are able to determine that quasars are small because they show variability over a short period of time, sometimes as short as hours or days. This indicates that the source of the radiation is very small, possibly the size of a solar system or even smaller.

Question 8

Most galaxies appear to be
A)composed of one star and seven planets.
B)inside our Milky Way.
C)located on the Earth.
D)moving toward us.
E)moving away from us.

Accepted Answer

According to Hubble's Law, galaxies are moving away from us, which is observed through redshift. This is known as the cosmological redshift and is evidence for the expansion of the universe.

Question 9

Many disk galaxies, such as Andromeda and the Milky Way, are thought to have extended halos of dark matter because the disk circular orbital speed is observed to ____________ increasing distances from the disk center.
A)stay constant with
B)decrease with
C)be totally absent at

Accepted Answer

The observed circular orbital speeds in disk galaxies like Andromeda and the Milky Way stay roughly constant even at increasing distances from the disk center, which is unexpected under Newtonian dynamics assuming only the visible matter contributes to the galaxy's mass. This discrepancy is one of the key pieces of evidence for the existence of dark matter halos surrounding these galaxies.

Question 10

Via the rotation curve method, we can estimate the mass of galaxies like M31 from
A)Doppler shifts of material at the edge of its disk and computing P = 2πr/v.
B)the distances of the Doppler shift points from its center.
C)Doppler shifts of material at the edge of its disk and computing P = 2πr/v and the distances of the Doppler shift points from its center.
D)It is impossible to estimate the mass of M31.

Accepted Answer

The rotation curve method involves measuring Doppler shifts of material at the edge of a galaxy's disk and using the equation P = 2πr/v to determine the mass enclosed within a given radius. By measuring the distances of the Doppler shift points from the center of the galaxy, we can trace out the shape of the rotation curve and estimate the total mass of the galaxy. Choice C includes both of these elements and is therefore the best choice.

Question 11

Which one of the words below is a name for a type of galaxy in the Hubble classification system
A)red giant
B)visual
C)spiral
D)21-centimeter
E)statuesque

Accepted Answer

The Hubble classification system categorizes galaxies based on their appearance, and one of the categories is spiral galaxies. The other choices are not types of galaxies in this classification system.

Question 12

What is the major observational difference between a Seyfert galaxy and a normal spiral galaxy
A)Normal spiral galaxies usually have shorter spiral arms.
B)Normal spiral galaxies never contain a supermassive black hole at their center.
C)The central region of a Seyfert galaxy is much brighter.
D)Seyfert galaxies don't contain any star formation.

Accepted Answer

The major observational difference between a Seyfert galaxy and a normal spiral galaxy is that the central region of a Seyfert galaxy is much brighter. Seyfert galaxies have an extremely bright and active galactic nucleus, powered by a supermassive black hole surrounded by an accretion disk. This leads to emission of bright and high-energy radiation, making the central region of the galaxy much brighter compared to a normal spiral galaxy which has a relatively inactive center.

Question 13

If Hubble's constant is taken to be 70 km/s/Mpc, and a quasar is found with a radial velocity of 0.95 times the speed of light, how far away is the quasar
A)4100 Mpc
B)0.014 Mpc
C)67 Mpc
D)74 Mpc
E)300,000 Mpc

Accepted Answer

Hubble's Law states that the velocity at which an object is receding from us is proportional to its distance, and this proportionality constant is known as Hubble's constant (H0). The equation for Hubble's Law is:

v = H0 x d

Where:
v = radial velocity of the object
d = distance to the object

In this question, we are given the value of Hubble's constant as 70 km/s/Mpc and the radial velocity of the quasar as 0.95 times the speed of light, which is approximately 285,000 km/s. We can convert this to km/s/Mpc by dividing it by the speed of light, which is approximately 3 x 10^5 km/s. Therefore:

v = 0.95 x 3 x 10^5 / 1 Mpc = 285 km/s/Mpc

We can now use Hubble's Law to find the distance to the quasar:

d = v / H0 = 285 / 70 = 4.07 Mpc

Therefore, the answer is A) 4100 Mpc, which is the closest option to the calculated distance.

Question 14

Active galaxies are thought to have _______ in their centers.
A)accretion disks
B)massive black holes
C)accretion disks and massive black holes
D)the Local Group
E)a cluster of galaxies

Accepted Answer

Active galaxies are believed to have both accretion disks and massive black holes at their centers. The accretion disk, by the force of gravity, pulls in matter and gases that heat up and emit intense radiation, making the galaxy appear bright and active. The center of the accretion disk is believed to harbor a supermassive black hole, a gravitational sinkhole with a mass millions or billions times greater than the Sun. The black hole pulls in the material from the disk, causing a surge in activity observed as jets or outflows of matter. Therefore, both accretion disks and massive black holes are the contributing factors to the activity of active galaxies.

Question 15

The unified model describes active galactic nuclei using
A)a supermassive black hole at the center of a normal spiral galaxy.
B)a supermassive black hole surrounded by an accretion disk and dense disk of gas.
C)an accretion disk around a neutron star.
D)gravitational lenses to intensify the radiation coming from them.
E)different lines of sight toward and dwarf irregular galaxy.

Accepted Answer

The unified model proposes that active galactic nuclei are powered by a supermassive black hole surrounded by an accretion disk and a dense torus of gas and dust. This model can explain the observed differences in their appearance depending on the orientation of our line of sight toward them.

Question 16

The figure shows an image of a galaxy at dust-penetrating wavelengths. It can be classified as which one of the following galactic types 
A)spiral
B)irregular
C)elliptical
D)red giant

Accepted Answer

The answer of The figure shows an image of a...

Question 17

How do astronomers know that the luminous regions of active nuclei of active galaxies are very small
A)Their nuclei are much brighter than expected.
B)The orbits of stars near the center of the galactic nuclei are faster than expected.
C)The luminosity of the nuclei varies over short times.
D)The color of the nuclei is different than expected.

Accepted Answer

The luminosity of the nuclei varies over short timescales, indicating that the region producing the light must be relatively small, as larger regions would take longer to change brightness significantly. This rapid variability is a key piece of evidence for the compact size of the luminous regions in active galactic nuclei.

Question 18

If a quasar has a recessional velocity of $2.7 × 10^5$ km/s and is determined to be 3600 Mpc, what is the Hubble constant based on this quasar alone Hint: Note that the units of your result should be (km/s)/Mpc to see what arithmetic process you need to perform.
A)50 km/s/Mpc
B)$9.7 × 10^8$ (km/s)Mpc
C)75 km/s/Mpc
D)0.013 km/s/Mpc
E)273,600 km/s/Mpc

Accepted Answer

Using Hubble's law, we have:

v = H0d

where v is the recessional velocity of the quasar and d is its distance in Mpc. Rearranging this equation gives:

H0 = v/d

Substituting the given values, we get:

H0 = (2.7 × 10^5 km/s) / (3600 Mpc)

H0 ≈ 75 km/s/Mpc

Therefore, the best choice is C.

Question 19

The hydrogen Balmer line Hβ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the change in wavelength (in nm) of this quasar Is it a "redshift" or "blueshift"
A)0; no change
B)2430.5; redshift
C)486.1; blue shift
D)1944.4; blueshift
E)1944.4; redshift

Accepted Answer

The change in wavelength is the observed wavelength minus the original wavelength, which is 2430.5 nm - 486.1 nm = 1944.4 nm. Since the observed wavelength is longer than the original, this is a redshift, indicating the quasar is moving away from us.

Question 20

The hydrogen Balmer line Hβ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the fractional change in wavelength or redshift z of this quasar
A)5
B)0.5
C)0.25
D)4
E)1944.4

Accepted Answer

We can use the formula for redshift, given by:

z = (observed wavelength - rest wavelength)/(rest wavelength)

Plugging in the values given, we get:

z = (2430.5 nm - 486.1 nm)/486.1 nm
z = 4.98

Therefore, the fractional change in wavelength or redshift of this quasar is approximately 4.98, which is closest to answer choice D (4).

Quiz 13: Galaxies: Normal and Active

Which kind of active galaxies has been observed at the greatest distances from us

The diagram illustrates physical size and angular size as seen by the observer. We can estimate the size in light years (or parsecs or km) of M31 from

Why do astronomers believe supermassive black holes are the source of an AGN's energy

Recent high resolution radio observations show that quasars can be classified as

Astronomers who discovered quasars found that they show _ of their spectral lines and are thus probably much _ than nearby galaxies.

Jet-shaped regions of radio and optical emission have been observed in

How are astronomers able to determine that quasars are so small

Most galaxies appear to be

Many disk galaxies, such as Andromeda and the Milky Way, are thought to have extended halos of dark matter because the disk circular orbital speed is observed to ____________ increasing distances from the disk center.

Via the rotation curve method, we can estimate the mass of galaxies like M31 from

Which one of the words below is a name for a type of galaxy in the Hubble classification system

What is the major observational difference between a Seyfert galaxy and a normal spiral galaxy

If Hubble's constant is taken to be 70 km/s/Mpc, and a quasar is found with a radial velocity of 0.95 times the speed of light, how far away is the quasar

Active galaxies are thought to have _______ in their centers.

The unified model describes active galactic nuclei using

The figure shows an image of a galaxy at dust-penetrating wavelengths. It can be classified as which one of the following galactic types

How do astronomers know that the luminous regions of active nuclei of active galaxies are very small

If a quasar has a recessional velocity of $2.7 × 10^5$ km/s and is determined to be 3600 Mpc, what is the Hubble constant based on this quasar alone Hint: Note that the units of your result should be (km/s) /Mpc to see what arithmetic process you need to perform.

The hydrogen Balmer line Hβ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the change in wavelength (in nm) of this quasar Is it a "redshift" or "blueshift"

The hydrogen Balmer line Hβ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the fractional change in wavelength or redshift z of this quasar