Nas 130: Quiz 8

What is the difference between visible light and X-rays?

Wavelength; X-rays have a shorter wavelength than visible light.

The first generation of stars most likely formed __________ when the stars died.

black holes

What is required to determine the luminosity of a star?

both distance and brightness

Essentially all the elements heavier than iron in our galaxy were formed

by supernovae.

If the quantum fluctuations imprinted on the dark matter halos at the time of the formation of the cosmic microwave background radiation were 10 times larger, galaxies would likely be

larger.

What objects are found in the thick disk of the Milky Way Galaxy?

older stars.

A grand unified theory unites which forces?

only electromagnetism, weak nuclear, and strong nuclear

The energy that powers the Sun is generated

only in its core.

We expect the galaxies that we see at a redshift of 4 (that is, when the universe was much younger) will be intrinsically __________ than galaxies today.

smaller and bluer

What is the size of the region responsible for powering an AGN?

solar system size

Examine the following image. The tilted gamma-ray jets emanating from the center of the Milky Way Galaxy are likely evidence that

the accretion disk around the supermassive black hole is also tilted.

Light is increasingly redshifted near a black hole because

time is moving increasingly slower in the observer's frame of reference.

The inverse of the value of H0 is a

time.

Why can't dark matter halos collapse to be the same size as the visible parts of galaxies? Dark matter

can't dissipate its energy through radiation.

An iron core cannot support a massive main-sequence star because iron

cannot fuse with other nuclei to produce energy.

The scientific method is a process by which scientists

gain confidence in theories by failing to prove them wrong.

The fact that the Milky Way has orbiting companion galaxies and is currently "eating" one of them is evidence that

galaxies form by mergers of smaller protogalaxies.

In the proton-proton chain, the net reaction is that four hydrogen nuclei are converted to one helium nucleus and __________ are released.

gamma-ray photons and neutrinos

Soon after the Big Bang, we think the four fundamental forces of nature were united into one superforce, and __________ was the first to split off from the others.

gravity

What process is most responsible for shaping the large-scale structure of the universe?

gravity

Sunspots appear dark because they

have lower temperatures.

By the time the universe was a few minutes old, the majority of the normal matter in the universe was hydrogen, and the remainder was mostly __________.

helium

The collapse of the core of a high-mass star at the end of its life lasts approximately

1 second.

The Sun will likely stop being a main-sequence star in

5 billion years.

How much of the total mass of the universe is made up of hot dark matter?

5 percent

The critical density of the universe is approximately equal to

1 proton per cubic meter (m3).

State the uncertainty (in arcseconds) for parallaxes measured by the Hipparcos satellite.

.001

The bulk of the Sun's energy generation is contained within a region of

0.2 solar radii.

In a binary star system that contains stars with 10 M¤ and 5 M¤, the velocity of the 10 M¤ star will be __________ times the velocity of the 5 M¤ star.

0.5

Which star spends the most time as a main-sequence star?

0.5 M¤

About what was the temperature of the universe when photons were no longer colliding with enough energy to create electron and positron pairs?

1 billion K

If Earth were to be condensed in size until it became a black hole, its Schwarzschild radius would be

1 centimeter (cm).

If your weight on the Moon is 1/6 your weight on Earth, what is the acceleration caused by gravity on the Moon?

1.60 m/s2

Which star spends the least time as a main-sequence star?

10 M¤

Astronomers have known that galaxies are separate entities outside of our own for roughly the past

100 years.

Approximately how long does it take the energy of the photons released in nuclear reactions in the core of the Sun to exit the photosphere?

100,000 years

The Sun's magnetic field reverses polarity every

11 years.

What is the diameter of the region depicted here with this collection of galaxies?

2 megaparsecs (Mpc)

In a star that has a chemical abundance similar to the Sun, what percentage of its mass is made of heavy elements?

2 percent

The speed of light in a vacuum is

300,000 km/s.

What is the current composition of the Sun's core?

35 percent hydrogen; 65 percent helium

What is the minimum-mass main-sequence star that becomes a Type II supernova?

8 M¤

How much of the total mass of a typical galaxy, like the Milky Way, is composed of dark matter?

90 percent

Roughly what percentage of stars are main-sequence stars?

90 percent

What surprising result came of the highest resolution map of the CMB?

A cool spot was confirmed.

In the figure, a planet orbits the Sun. The line connecting the planet and Sun sweeps out three areas labeled A, B, and C, during three different time intervals. If the duration of the time intervals are the same (meaning t2 - t1 = t4 - t3 = t6 - t5), how are the sizes of these areas related?

A, B, and C have the same size.

As a beam of light travels from one medium to another, the change in direction of the beam of light depends on

All choices are true.

What is true about SN1987A (see the following image)?

All choices are true.

Our Milky Way Galaxy is a member of

All choices are valid.

Examine the following graph. What can be said about where the energy is generated in the sun?

All energy comes from the inner 30%.

The earliest isotopes of low-mass nuclei (deuterium, helium, lithium, beryllium, boron) were formed in a process called

Big Bang nucleosynthesis.

During which era will the final black holes decay?

Black Hole Era

Which era corresponds to the final stage of the universe?

Dark Era

Astronomers measuring the amount of normal matter in the universe found that it matches the amount predicted by Big Bang. What is the importance of this finding?

Dark matter cannot be made up primarily of normal matter, such as protons and neutrons.

How can massive compact halo objects (MACHOs) be directly detected?

Distant stars are brightened by gravitational lensing.

Which of the following methods is used to measure the velocity and direction of motion of gas in the galaxy?

Doppler effect

Which galaxy type is characterized by a spherical shape and a lack of spiral arms or disk structure?

E0

The following figure plots the chemical composition of the Sun as a function of radius for three different times. Which graph represents the correct chemical composition at the end of its main-sequence lifetime?

Figure C

What spectral class is the Sun?

G2

What do astronomers mean when they say that the universe is homogeneous?

Galaxies are generally distributed similarly throughout the universe.

Which scientist ended up under house arrest because of his support of the heliocentric model?

Galileo Galilei

Which of the following is a prediction of the standard Big Bang theory that has been successfully verified by observations?

Helium, lithium, and beryllium were made as the universe cooled soon after the initial Big Bang.

The standard model of particle physics is incomplete because it leaves which question(s) unanswered?

How is gravity related to the other three fundamental forces?

What is true about degenerate matter in a low-mass star as it evolves off the main sequence?

It doesn't expand as temperature increases.

How does the speed of light traveling through a medium (such as air or glass) compare to the speed of light in a vacuum?

It is always less than the speed of light in a vacuum.

What is the name of the region depicted here along with its collection of galaxies?

Local Group

Was the Big Bang an explosion that flung debris throughout space?

No, the Big Bang formed space and time in a rapid expansion.

After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

Photons began to travel freely through the universe.

In order from first to last, the specific eras in the universe's history are known as the

Primordial, Stelliferous, Degenerate, Black Hole, and Dark eras.

The speed of light was first determined by which scientist?

Rømer

Examine the following image. Which statement about the slopes in the plotted data is true?

Some are positive.

During which era will the last star form?

Stelliferous Era

Why does the expansion of space cause redshifts of distant galaxies?

The amount of space in between the galaxies is increasing.

In some particle physics theories, the universe must have more than three spatial dimensions, but we experience only three. Why would we not see the other spatial dimensions?

The other six spatial dimensions are tightly wrapped around each other and have not expanded.

Why was the discovery of dark energy unexpected?

The gravity provided by the mass contained within the universe was predicted to slow the expansion.

What do astronomers mean when they say that the universe is isotropic?

The universe appears the same no matter where you look.

What prevents us from looking all the way back to the Big Bang itself?

The very early universe was so hot that matter was ionized and photons were blocked by free electrons in the universe.

If the frequency of a beam of light were to double, how would that affect its wavelength?

The wavelength would be two times smaller.

What would the universe be like if there were complete symmetry between matter and antimatter?

There would be a universe, but it would be completely composed of photons.

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

These photons, which are produced by neutral hydrogen, penetrate the dense clouds of gas and dust in the disk.

What is observed to happen to the orbital velocity of stars as you measure them at increasing distances from the center of the galaxy?

They essentially stay the same.

The following figure indicates a possible picture of a theoretical universe with two separate observers within it. Which of the following statements describes this universe?

This universe is both homogeneous and isotropic.

Why can Type Ia supernovae be used to determine a galaxy's distance?

Type Ia supernova have approximately the same luminosity.

Which technique can measure distances to the edges of the observable universe?

Type Ia supernovae

At what stage in the universe's history do we think the asymmetry between matter and antimatter was created?

about the time the strong force separated out of the grand unified theory

In the absence of air friction, a 0.001-kg piece of paper and a 0.1-kg notebook are dropped and allowed to fall to the ground. How do their accelerations compare? The

accelerations are the same.

Which of the following statements is correct?

all of the above

The Maunder Minimum was a 60-year period when

almost no sunspots occurred on the Sun.

What do astronomers think will be the final state of our universe?

an ever-expanding universe filled with photons and elementary particles

Which of the following would decrease if a particular star was closer to Earth?

apparent magnitude

What is one similarity between star formation and galaxy formation? Both processes

are dominated by gravity.

Examine the galaxies in the following images. What prominent feature distinguishes the bottom row from the top row?

bar-shaped bulges

Which of the following provided the gravity to form galaxy fragments in the early universe?

cold dark matter halos

Axions and photinos are expected to be examples of

cold dark matter.

Local Group

cold dark matter.

What assumption about the universe is made using the Hubble time to estimate the age of the universe?

constant expansion

During the post main-sequence evolution of a massive star, increasingly heavier elements are fused in the core, giving the core support for

decreasingly shorter times.

Degenerate refers to a state of matter at high

density.

Where in the Milky Way would we look to find lots of gas and dust?

disk

If you measure the average brightness and pulsation period of a Cepheid variable star, you can also determine its

distance.

List the four fundamental forces of nature.

electromagnetic, gravity, strong nuclear, and weak nuclear

What material is degenerate in a low-mass star as it evolves off the main sequence?

electrons

In a white dwarf, what is the source of pressure that halts its contraction as it cools?

electrons packed so closely that they become incompressible

We currently live in the universe during its

era of stars.

If today and dark energy is a cosmological constant, the universe will

expand forever.

If today and there were no dark energy, the universe would

expand forever.

In the 1990s, astronomers found that distant Type Ia supernovae were __________ than they expected, leading them to conclude that __________.

fainter; the universe's expansion rate has been increasing with time

We can identify only a small fraction of all the pulsars that exist in our galaxy because

few swing their beam of synchrotron emission in our direction.

Our current ideas on galaxy formation suggest that the visible parts of galaxies

form only in the densest parts of dark matter halos.

A single 1-M¤ star will eventually eject significant amounts of which of the following chemical elements into the interstellar medium?

hydrogen

The early universe was composed mainly of which two elements?

hydrogen and helium

A main-sequence star is unique because

hydrogen burning occurs in its core.

Examine the following figure. On a typical H-R diagram, where are main-sequence stars that have the hottest surface temperatures located?

in the upper left corner

Density, temperature, and pressure __________ as you move inward in the interior of the Sun.

increase

According to Hubble's law, as the distance of a galaxy __________, its __________ increases.

increases; recessional velocity

An astronaut would feel __________ as he or she crossed the event horizon of a stellar black hole.

incredibly strong tidal forces

What can simultaneously solve both the flatness and horizon problems in cosmology?

inflation

How is the distance to a star related to its parallax? Distance is

inversely proportional to parallax.

Stars of the first generation were

more massive than today's average star.

Once carbon begins burning in the core of a high-mass star, the outer layers begin to fall inward, driving up the fusion rates and speeding up the star's evolution primarily because

most of the energy is now carried away from the core by escaping neutrinos, which have few if any obstacles to leaving the star.

The following figure shows the spectrum of a star (top) whose motion compared with our star is nearly stationary within the Milky Way Galaxy. The galaxy spectrum (bottom) indicates that the galaxy is

moving away from us.

The existence of the cosmic microwave background radiation tells us that the early universe was

much hotter than it is today.

Consider the following image of this planetary nebula. What measurements are needed to determine how long ago the parent star died?

nebula's radius and expansion velocity

Which of the following are expected to make up a significant amount of hot dark matter?

neutrinos

What remnant can be produced by the collapse and rebound of a massive star in a Type II supernova?

neutron star

How much would the force of gravity at the surface of the Earth differ if Earth's volume were increased 125 times and its mass was increased 25 times? (Hint: Volume is proportional to the cube of a sphere's radius.)

no difference

If you went out tonight and looked at the sky at midnight, at what time would you have to observe 6 months from now to find the stars in approximately the same position in the sky? Assume that you could see the stars at any time, day or night.

noon

When two atomic nuclei come together to form a new species of atom, it is called

nuclear fusion.

What observational evidence supports the idea that the Milky Way Galaxy was formed by a merger of several galaxies?

outer halo stars orbiting in the opposite direction of the Galaxy's rotation

What unit is defined as the distance a star has with a parallax of 1 arcsecond?

parsec (pc)

In the early 1960s, physicists named Penzias and Wilson detected a persistent noise at a wavelength of 1 millimeter (mm) in their radio telescope. The persistent noise that Penzias and Wilson detected came from all directions in the sky as a result of

photons leftover from the Big Bang.

What are positrons?

positively charged electrons

Cosmic rays are

primarily protons with very high energies.

What is the method used to measure the distances to the farthest galaxies when mapping out large-scale structures?

redshifts and Hubble's law

How would astronomers describe the antiparticle of an electron?

same mass but opposite charge

Stars of similar temperatures but different sizes will have

similar spectral types but different luminosities.

Structure formation in the universe proceeds hierarchically, meaning that

small objects collapse, then merge to form larger objects.

Galaxies move away from us in all directions because

space is expanding.

Star A is a blue star. Star B is a red star. Which is hotter?

star A

How would the linear fit and the value of H0 change in the following plot if the universe were expanding faster than it is today? The line would be

steeper and H0 would be bigger.

What force only acts at short distances of the order 10-15 meters?

strong nuclear force

Which of the following structures is the largest?

supercluster

The observed abundances of helium and deuterium in the universe

support models of Big Bang nucleosynthesis.

The patterns of walls and voids that are observed

support the cosmological principle.

What is demonstrated in the following figure?

synchronous rotation

What is the closest star to the Earth?

the Sun

What is a planetary nebula?

the ejected envelope of a giant star surrounding the remaining core of a star

The fact that we do not observe any stars with chemical compositions matching our predictions for the very first generation of stars implies that

the first stars died quickly, which implies a high mass.

What is ripping apart the Sagittarius dwarf spheroidal galaxy?

the gravitational tidal force of the Milky Way

Where are the most metal-rich stars found in the Milky Way?

the inner parts of the galaxy

All of the following are useful in determining the masses of stars in a binary system except:

the luminosities of the two stars.

Why does the overall mass and energy density of the universe decide its ultimate fate? The greater the density of the universe,

the more gravitationally bound the universe will be.

The slower-moving star in a binary is

the more massive star.

We observe different phases of the Moon because

the orbital position of the Moon determines which portion and how much of the facing lunar surface is illuminated by sunlight.

Whether or not parallel universes exist is hard to determine because

the parallel universes cannot communicate with each other.

In stellar fusion, the term ash refers to

the result of nuclear fusion that collects in the core.

Even with infinitely powerful telescopes, we can look back in time only until

the time of recombination.

Grand unified theories are very attractive because they can explain why

the universe consists mostly of matter.

The surface of the Sun appears sharp because the photosphere is

thin compared with the other layers in the Sun.

Why do reflecting telescopes usually have a secondary mirror in addition to a primary mirror?

to make the telescope shorter

The shortest day of the year for a person living in the Northern Hemisphere is the

winter solstice.

The first galaxies formed

within dark matter halos.