Astronomy 103 Final Exam UW Madison

Cepheid variable stars are important because

They show a periodic variation in their brightness, which is related to their luminosity

The HR diagram is a plot of

Intrinsic brightness or luminosity vs surface temperature of stars

The lifetime of a star is primarily determined by

The stellar mass

What occurrence defines the start of the main sequence phase of a star's life

When hydrogen fusion begins in the core

For some reason the center of the Sun suddenly became hotter. What would happen next?

An explosion would be triggered due to a runaway nuclear fusion reaction

Stars that formed 10 billion years ago with a tenth the mass of the Sun

All remain on the main sequence today

The most important development in the interior of a low-mass star which leads to the Red Giant phase is

The cessation of hydrogen "burning" in the core, leading to core contraction and overall star expansion

The characteristics of the interiors of white dwarfs are

Mainly carbon and oxygen nuclei, supported by electron degeneracy pressure in a volume about the size of Earth

If the turnoff point in a cluster HR diagram occurs at spectral type B. Then which of the following is true?

All O-type stars have evolved off the Main Sequence

The most massive stars generate energy at the end of their lives by fusing iron in their cores

False

Nuclear fission of heavy elements is a process that releases energy. From this we can deduce that

The product nuclei must have a lower mass than the original nucleus that fissions

Which of the following is never a consequence of a supernova explosion

The formation of a planetary nebula

A neutron star is expected to spin rapidly, because

It conserved angular momentum when the star collapsed

From an observational standpoint, what is a pulsar?

An object that emits flashes of light several times per second or more, with near perfect regularity

You discover a binary system in which one star is a 15 solar mass main sequence and the other is a 10 solar mass giant. How might such a star system have come to exist?

The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion

A nova is almost always associated with

A white dwarf in a close binary system

Diana took of on a trip...

She stays still, while the Earth rushes away from her

Why do we see a gravitational redshift in the spectrum of the Sun?

Time runs slower on the Sun than on the Earth, making lines in the solar spectrum have lower frequencies and hence longer wavelengths than normal

In order for gravitational lensing of a distant quasar to occur, the galaxy producing the lensing must

Be almost perfectly placed in a line between Earth and the quasar

The structure of a black hole can be described simply as

A singularity and an event horizon

Which of the following statements about black holes is not true?

If the sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole

What does "standard candle" mean for cosmology

It is an object of known luminosity, used to measure distance.

Cepheid variable stars are located in two different galaxies A and B. The star in galaxy A has a bright-dim-bright period of 10 days, while the same on in galaxy B has a bright-dim-bright period of 30 days. Which of the two stars has the greater average luminosity?

The one in galaxy B

What was the implication of the observation by Edwin Hubble that the Cepheid variable stars that he measured in the Andromeda Nebula appeared to be very faint compared with that was expected?

The Andromeda Nebula was very far away and was in fact not a nebula.

According to the Hubble Law, if galaxy A is twice as distant as galaxy B, then galaxy A is receding

Twice as fast as B

What is the "cosmological redshift"?

The stretching of the wavelengths of photons as they travel through expanding space.

Suppose that at the same time on the same night we see one supernova in the Andromeda galaxy, 2 million light-years away from us, and another in galaxy M82, 6 million light years away from us. Which of the following statements is correct?

The supernova in the Andromeda galaxy actually occurred after the one in M82

The position of the Sun in the Milky Way is best described as

In the disk, roughly half way out

In the halo of the Milky Way we can find

The oldest stars in our galaxy, extending in a sphere 100,000 or more light years in diameter

How are the large and small Magellanic clouds, the two nearby satellite galaxies of the milky way classified?

Irregular galaxies

Starburst galaxies

Are often associated with a galaxy that is colliding with another galaxy

Which of the following features is not a feature of cD (central dominant) galaxy?

They are often spiral galaxies

Features of central dominant galaxies include

They are found in clusters of galaxies, they often have multiple galactic nuclei near their centers, and they are thought to form by the merger of several smaller galaxies.

The Milky Way galaxy is a part of

The Local Group

The rotation curve of a galaxy can be used to determine

The mass of the galaxy

The formula M=rv2/G measures

Only the mass Minterior to the point where the measurement is made

A "mass to light" (M /L ) ratio of 30 for a galaxy implies that

most of the galaxy's mass must be in non-luminous matter.

Clusters of galaxies are 50% dark matter, most of which is in the form of hot, X-ray emitting gas.

False

Observations of gravitational lensing of stars in the Large Magellanic Clouds are used

to test for the presence of compact, non-luminous stars in the halo of the Milky Way (i.e., MACHOs).

What recent evidence now indicates that nearby galaxies may contain supermassive blackholes at their centers?

Spectroscopic observations of stars near the centers of these galaxies show extremely high orbital velocities, which requires large-mass objects to retain the stars in orbit.

Accretion disks power quasars." Where does the power come from?

Release of gravitational energy as matter falls toward a black hole.

Why might a galaxy with a supermassive black hole at its center give off detectable X-rays?

Gas falling into the black hole from an accretion disk will become very hot and emit X-rays.

Which scientist discovered that his theory predicted an expanding universe, and because he doubted the existence of expansion, he modified his equations?

Albert Einstein

The effect of a positive Λforce on the expansion of the universe is

to increase the expansion rate over what it would have without Λ.

Which of the following elements is NOT formed as a result of nuclear fusion inside stars?

Hydrogen

What elements are formed as a result of nuclear fusion?

Helium, carbon, oxygen, and iron

The cosmic microwave background consists of photons that were released from their constant interactions with matter at a time coincident to another important event. Which one of the following events coincided with the formation of the cosmic microwave back-ground?

The time during which most of the ionized matter in the Universe became neutral.

What is required to reionize the gas to end the Dark Ages?

Light with energy above the threshold for ionizing hydrogen.

When did the first stars form?

During the Dark Ages

Our knowledge of Physics breaks down when we get very close to the time of the BigBang. How close?

To within the Planck era

If the Big Bang cosmology is correct, then

Nearby galaxies are seen at a more advanced stage of evolution than distant galaxies.

Smaller structures like galaxies formed before clusters and superclusters. This process is known as

Hierarchical clustering

Inflationary models of the universe can explain all of the following EXCEPT why

Galaxies have spiral arms

Opposite sides of the universe have the same temperature, yet according to the standardBig Bang Theory, these points are too far apart for light to have traveled from one side to the other in the age of the universe; i.e., they cannot have exchanged heat to even out their temperature. Why, then, do they have the same temperature?

They were originally close together and evened out their temperature, then a rapid inflation of the universe carried them far apart.

If inflation occurred, then our observable universe is only a tiny portion of the entire universe born in the Big Bang.

True

If the rotation curve of a galaxy continues to rise at large radii, what can we infer about the distribution of galactic mass?

There is substantial mass at large radii

You observe that the elliptical galaxy NGC 4889 has a redshift z = 0.04. How far away is this galaxy?

171 Mpc

Two massive stars orbit each other with a period of 50 years and a separation of 20 AU. If one star is 2 times more massive what are the individual masses of the two stars?

1M, 2M

Radio galaxies have huge lobes of radio emission originating from:

High-speed electrons shooting out of the nucleus and spiraling through a magnetic field

If Andromeda was half as far away from the Earth, its angular size would be

Twice as big

You observe a triple stellar system, you can be sure that the orbital period of the star that is closest to the center of mass is:

Shorter than for the two other stars

The main physical difference between spiral and elliptical galaxies is that

Elliptical galaxies contain mostly old stars while spiral galaxies contain also young stars

Two stars are of exactly the same spectral type, but star A has a radius 10 times smaller than the radius of star B. You can conclude that

Star A is 100 times less luminous than star B

Because nearly all galaxies are moving away from us, we must be located at the center of the universe.

No, everything moves away from everything else in an expanding Universe there is no unique center

An emission nebula is

A cloud of hydrogen ionized by young stars found in spiral arms

Gravitational lensing occurs when:

Light passes near a massive object and is deflected by the object's gravitational field

The Cosmic background Explorer satellite (COBE) detected small scale brightness fluctuations in the cosmic microwave background (CMB) radiation. This is a big discovery because

The Big Bang theory predicts that the CMB should be uniform

How would you order these objects in terms of increasing brightness

Epsilon Indi, the Small Magellanic Cloud, Sirus A, Moon

What is an irregular galaxy currently interacting with the Milky Way and being torn apart by the Milky Way's gravitational influence

The Small Magellanic Cloud

What is the correct order of evolutionary stages for a star of 5 Solar masses?

Protostar, main sequence, red giant, planetary nebula + white dwarf

If two straight lines start out parallel but eventually cross, what type of geometry are we dealing with?

Closed or spherical

After a star depletes its hydrogen fuel and contracts to a core temperature of 100 million degrees, energy is generated by:

Triple-helium (alpha) reaction

The exact value of Hubble's constant is not known precisely. If Hubble's constant would increase by a factor of 100 from its current value, how would this affect our estimate of the age of the Universe?

The universe would be estimated to be 100 times younger

High-mass stars live _____ than low-mass stars because:

Less long, the burn their fuel faster even though they have more fuel

A Roche Lobe is

The zone in a double star system that marks the region of gravitational influence for each star

The Sun is 27% helium by mass. Where was the majority of this helium produced?

In thermonuclear reactions during the first few minutes after the Big Bang

The fundamental discovery made by Penzias and Wilson at Bell Labs in the mid-1960s was

Very uniform radio emission consistent with light leftover from the Big Bang

If the Big Bang theory is right, a billion years from now the night sky will

Be brighter as the light away from many more galaxies will be able to reach us

The Sagittarius dwarf galaxy is a small galaxy orbiting around the Milky Way at a distance of 20 kpc. If the mass of the Milky Way is 2x10^12 M then what is the orbital speed of the Sagittarius dwarf galaxy?

660 km/sec

The position of the Sun in the Milky Way is best described as:

In the disk, slightly more than halfway out

Hubble's Law relates which two physical quantities of galaxies

Distance and recessional velocity

The current redshift record holder is a galaxy z = 6.69. How does the size of the Universe today compare with the size of the Universe when the light was emitted from this galaxy?

The Universe today is about 7 times larger

You observed the 21.1 cm line of atomic hydrigen from a high-redshift galaxy located at a distance of 3950 Mpc. At what wavelength do you expect to detect atomic hydrogen emission from this galaxy?

About 40 cm

If all of these objects have the same mass, which one has the largest escape velocity?

Neutron Star

What technique do astronomers use to see how and if a galaxy is rotating?

Doppler shift measurements of stars and gas in a galaxy

What is the furthest thing we can see in the Universe?

The cosmic microwave background radiation

Which of the following would you use as a standard candle?

A Cepheid variable star

Observations of motions of stars near the Galactic center probe

The mass of the central black hole

If a red star and a blue star both have the same radius and both are the same distance from Earth, which one looks brighter in the night sky?

Blue star looks brighter than the red star

Which of the following does not exhibit intense radio emission?

Dwarf galaxies

Shapley located the enter of the Milky Way by studying the distribution in space of

Milky Way globular clusters

Why are spiral arms in the Andromeda galaxy bright at visual wavelengths?

Because they contain more hot young stars than other parts of the gaaxy

Which is closest?

A dwarf galaxy with a redshift z = 0.002

To find a star in its earliest stage of formation you should look at objects

That emit strong infrared emission

Imagine you measure the density of matter in the Universe and find that is equals 0.5. If there was no dark energy, what will be the fate of this universe?

It will keep expanding for ever but slow down slightly

What is the Chandrasekhar limit?

The maximum possible size of a white dwarf

Astronomers currently think that the radiation coming from quasars originates from

A disk orbiting a supermassive black hole

Which of the following is true about a core collapse (Type 2) supernova?

It has strong hydrogen lines in their spectra, produced from star's former atmosphere

A 10 solar mass black hole swallows a 5 solar mass star. What happens to the size of its event horizon?

It increased by a factor of 1.5

Observations of Type 1a supernovae in distant galaxies confirm that the expansion of the Universe is decreasing overtime?

False