Question 1

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

Accepted Answer

To estimate the size in light years (or parsecs or km) of M31, we need both its angular size and distance. From the given image, we can estimate the angular size of M31 to be approximately 3 degrees.

To find the distance to M31, we can use the relationship between distance, size, and angular size:

distance (in parsecs) = size (in parsecs) / angular size (in radians)

Since we don't have the size of M31 in parsecs, we can use its size in light years and a conversion factor:

1 parsec = 3.26 light years

Therefore,

distance (in light years) = size (in light years) / (angular size (in degrees) * 3.26)

Using a known size of M31 (approximately 220,000 light years) and the estimated angular size (3 degrees), we can estimate the distance to M31 to be approximately 2.5 million light years.

Therefore, the best choice is C: its angular size in degrees and its distance in light years (or parsecs or km).

Question 2

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

Accepted Answer

The Hubble classification system recognizes three main types of galaxies: elliptical, spiral, and irregular. Out of the given choices, only "spiral" is a name for a type of galaxy in this system.

Question 3

If a quasar has a recessional velocity of 2.7 × 10⁵ 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.

Accepted Answer

The Hubble constant (H₀) is calculated by dividing the recessional velocity by the distance: H₀ = (2.7 × 10⁵ km/s) / 3600 Mpc = 75 km/s/Mpc.

Question 4

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

Accepted Answer

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

Question 5

The hydrogen Balmer line H_β 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?

Accepted Answer

Using the formula for redshift, z = (λ(observed) - λ(rest)) / λ(rest), we get z = (2430.5 nm - 486.1 nm) / 486.1 nm = 4.99, which is closest to choice D. Therefore, the answer is D.

Question 6

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

Accepted Answer

Quasars show large redshifts of their spectral lines, indicating that they are moving away from us at high speeds and are farther away than nearby galaxies.

Question 7

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

Accepted Answer

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

Question 8

How are astronomers able to determine that quasars are so small?

Accepted Answer

Astronomers are able to determine that quasars are small by observing their variability over a short period of time. This can only happen if the source is relatively small, as larger sources would take longer to vary.

Question 9

Most galaxies appear to be

Accepted Answer

The observation of redshift in the light spectrum of distant galaxies indicates that they are moving away from us, which is consistent with the expansion of the universe.

Question 10

Active galaxies are thought to have _______ in their centers.

Accepted Answer

Active galaxies have both accretion disks and massive black holes in their centers. The black hole's strong gravitational pull can pull in nearby materials (such as gas) from the disk and heat them, causing the disk to emit high-energy radiation that can be observed as the galaxy's activity.

Question 11

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

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 12

The hydrogen Balmer line H_β 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"?

Accepted Answer

The change in wavelength is 2430.5 nm - 486.1 nm = 1944.4 nm. Since the observed wavelength is longer than the laboratory wavelength, it is a redshift.

Question 13

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

Accepted Answer

Quasars are the most distant active galaxies observed, with some being billions of light-years away. Seyfert galaxies and radio galaxies are also active galaxies, but they have not been observed at the same distances as quasars.

Question 14

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

Accepted Answer

The rotation curve method involves measuring the Doppler shifts of material at the edge of a galaxy's disk and computing the period of its orbit using the formula P = 2 π r / v, where r is the distance from the center of the galaxy and v is the velocity of the material. By measuring many points along the rotation curve, we can estimate the mass distribution of the galaxy. Therefore, choice C combines both important components of the rotation curve method.

Question 15

The unified model describes active galactic nuclei using

Accepted Answer

The unified model describes active galactic nuclei as a supermassive black hole surrounded by an accretion disk and dense disk of gas. This model unifies different types of active galactic nuclei based on their observed properties, such as the orientation of the observer with respect to the accretion disk. Therefore, B is the best choice.

Question 16

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

Accepted Answer

Recent high resolution radio observations show that quasars can be classified as a kind of active galaxy similar to Seyfert and radio galaxies.

Question 17

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

Accepted Answer

Choice A states that supermassive black holes have been found at the center of most galaxies, both active and inactive, which suggests that they are likely the source of an AGN's energy. Choice B states that radio jets are seen from low-mass black holes plus accretion disks inside our galaxy, which may suggest a relationship between black holes and AGNs, but this doesn't necessarily mean that supermassive black holes are the source of an AGN's energy. Choice C states that jets and accretion disks have been observed in active galaxies, which supports the idea that AGNs are powered by some sort of accretion process, but doesn't specifically tie it to supermassive black holes. Choice D is also a valid reason for why astronomers might believe supermassive black holes are the source of an AGN's energy, as a black hole's immense gravitational energy could be released as radiation through accretion. Therefore, the best choice is E, as all of the other choices are correct and support the idea that supermassive black holes are the source of an AGN's energy.

Question 18

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.

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 19

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?

Accepted Answer

Using Hubble's law:

v = H0*d

where v is the radial velocity, H0 is Hubble's constant, and d is the distance to the quasar.

Solving for d:

d = v/H0

Plugging in the given values:

d = (0.95c) / (70 km/s/Mpc)

where c is the speed of light.

Converting units and solving:

d = (0.95*3.00*10^5 km/s) / (70 km/s/Mpc)

d = 40,500 Mpc

The correct answer is A), which is 4100 Mpc after rounding to one significant digit.

Question 20

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

Accepted Answer

The central region of a Seyfert galaxy is much brighter due to the presence of an actively accreting supermassive black hole at its center, which emits strong radiation in the form of non-thermal ionizing radiation, producing broad emission lines in the spectrum. In contrast, normal spiral galaxies have a much fainter central region, without any strong non-thermal emission lines. Therefore, the major observational difference between a Seyfert galaxy and a normal spiral galaxy is the brightness of their central region, particularly in the optical and UV bands.

Quiz 13: Galaxies: Normal and Active

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

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

If a quasar has a recessional velocity of 2.7 × 10⁵ 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 figure shows an image of a galaxy at dust-penetrating wavelengths. It can be classified as which one of the following galactic types?

The hydrogen Balmer line H_β 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?

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

Active galaxies are thought to have _______ in their centers.

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

The hydrogen Balmer line H_β 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"?

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

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

The unified model describes active galactic nuclei using

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

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

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.

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?

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

Quiz 13: Galaxies: Normal and Active

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

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

If a quasar has a recessional velocity of 2.7 × 105 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 figure shows an image of a galaxy at dust-penetrating wavelengths. It can be classified as which one of the following galactic types?

The hydrogen Balmer line H β 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?

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

Active galaxies are thought to have _______ in their centers.

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

The hydrogen Balmer line H β 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"?

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

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

The unified model describes active galactic nuclei using

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

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

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.

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?

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

If a quasar has a recessional velocity of 2.7 × 10⁵ 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 H_β 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?

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

The hydrogen Balmer line H_β 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"?