Astronomy 123 Final Exam

Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:

A cloud of gas or star that is further from the center will generally take more time to orbit

At the end of the p-p chain of nuclear fusion in the sun, hydrogen nuclei have been converted into:

A helium nucleus

According to the formula E=mc^2

A little bit of mass can be converted into a substantial amount of energy

In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case why do galaxies show a redshift?

As space stretches, the waves of radiation in space also stretch and their wavelength increases

Why did Einstein introduce the cosmological constant into the equations of his general Theory of Relativity when describing the universe?

Einstein's equations required the universe to expand or contract; he could not imagine or accept it doing either one, so he put a factor in to stop it from moving

If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be

Equal to zero- you would be weightless

Which of the following statements about the implications of Hubble's Law is FALSE

If you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from you

You are alone in a large, completely dark auditorium on Earth. What kind of telescope should I use from the other side of the auditorium to detect electromagnetic radiation emitted by your body?

Infrared

After the big bang, in order for the universe to become transparent to light and other electromagnetic radiation, what had to happen?

The universe had to cool enough to allow neutral hydrogen to form

Astronomers now have a good idea for explaining how the short-duration gamma-ray bursts might come about. Which of the following is part of their explanation?

These bursts most likely come from the merger of two neutron stars

What have we learned from the work of Harlow Shapley and others about the location of the sun in the Milky Way galaxy?

We are in the disk of the galaxy, about 3/5 of the way from the center

When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?

a few billion years ago

At first, right after the big bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form?

a few thousand years

In the p-p process, the missing product is

a helium nucleus

Which of the following produced at the core of the sun, will take the shortest time to emerge from the Sun's photosphere (surface)?

a neutrino

When the mass of a star's core is greater than 1.4 times the mass of the Sun degenerate electrons can't keep it stable as a white dwarf. Instead, it becomes

a neutron star

What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?

1/2 the diameter of the Earth's orbit around the Sun

The gravitational wave signal from merging black holes is called a chirp because

As the black holes get closer, the signal frequency and amplitude increase

Which of the following statements about the life of a star with a mass like the Sun is correct

As the star is dying, a considerable part of its mass will be lost into space

Today we believe that only a small number of elements were actually formed during the big bang. Which was not one?

Carbon

Which of the following statements about the different types (shapes) of galaxies is correct?

Collisions and mergers between galaxies can sometimes change a galaxy's type (shape)

Once a black hole forms, the size of its event horizon is determined only by

the mass inside the event horizon

We now know that most of the heaviest elements such as gold are created in

the merger of binary neutron star systems

Having two LIGO detectors separated by 3000km is important because

true signals would be observed in both detectors and the time of arrival of signals can be used to find the position of sources (a+c)

The process of fusion that keeps our Sun shining begins with which building blocks?

two protons

When a single star with a mass equal to the sun dies, it will become a

white dwarf

Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?

you must take a spectrum of the galaxy and measure the redshift

When we determine the age of the universe using Hubbe Time (1/Ho), what important simplifying assumption goes into our calculations

That the expansion of the universe has been happening at the same rate- neither speeding up or slowing down

When astronauts aboard the International Space Station (ISS) in space and let go of an orange, it ends up floating Why?

The ISS is falling around the Earth, and in free fall, things feel no weight

If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use

a satellite with infrared and microwave telescopes on board

The objects created by the merger of two black holes is

a single black hole with mass slightly lower than the sum of the merging ones

Two stars are giving off electromagnetic radiation. The hotter star will

a. give off more radiation at all wavelengths b. will have a shorter average wavelength of radiation c. will radiate energy at more than one wavelength d. will give off a continuous spectrum of waves e. ALL OF THE ABOVE

The nucleus of the hydrogen atom

a. has a positive electrical charge b. is an ingredient in the fusion process in the sun c. a proton d. ALL OF THE ABOVE

Which of the following is not a candidate for the identity of dark matter

anti matter or MACHO'S

General relativity predicts that light passing near a massive object like the sun will

appear bent when observed from earth

Measurements of the cosmic microwave background provide strong evidence that the overall geometry of space is

flat, or zero curvature

When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays coming from?

from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)

Which of the following statements about dark matter is FALSE

astronomers have a pretty good idea what the dark matter is made of

Merging black holes can only be observed

from their gravitational wave emission

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

fusing hydrogen into helium in their cores

What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized

galaxy groups are organized into huge filaments with great voids between them

The most prolifically created nuclear species in big bang nucleosynthesis is

helium 4 4He

The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this, we may include that

his particular galaxy is moving toward us

In a distant galaxy, light that is arriving from 10 billion light-years away, our spectroscope should reveal that the most common element is

hydrogen

If we want to see what galaxies looked like at a time close to the beginning of the universe where should we look?

in a direction away from the plane of the milky way, where we can see very faint galaxies that are more than 10 billion light years away

How does a period of extremely fast inflation very early in the history of the universe explain the observation that the geometry of the universe looks flat (not curved) to us?

inflation increased the size of the universe so much that the resulting universe looks flat from any point of view

According to the cosmological principle, the universe

is isotropic and homogenous

What happens to the position created during the p-p chain of nuclear reactions inside the sun?

it quickly collides with an electron and turns into gamma-ray energy

How long a main sequence star remains on the main sequence depends most strongly on

its mass

Which of the following does not happen when two galaxies collide?

many of the stars in one galaxy collide with the stars in the other

The core of neutron stars consists of

matter with super-nuclear density in a form we don't know for sure

In describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same is all directions) What recent observations have confirmed that the universe is isotropic on the large scale

measurements of the cosmic microwave background radiation

We now know that most heavy elements such as gold are produced in

neutron star mergers

In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into:

neutrons and neutrinos

When a large nucleus breaks apart (or is broken apart) into smaller pieces, this is called

nuclear fission

Today we realize that the source of energy from the Sun is a process called

nuclear fusion

The three pillars of evidence for big bang cosmology are the cosmological redshift, the cosmic microwave background and

nucleosynthesis

Special relativity gives a "speed limit: meaning that

objects cannot move faster than the speed of light

The sun is composed of matter in the form of

plasma

Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is

about 13.8 billion years

The antimatter version of an electron is called a

positron

Which of the following is a candidate for the identity of dark matter

primordial black holes and weakly interacting elementary particles

THe 170817 event demonstrated that neutron star mergers

produce gamma ray bursts, gravitational waves, heavy elements, and kilonova afterglows

Which of the following has the longest wavelength

radio waves

Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today are generally

redder and smaller

When a star or galaxy is moving away from us, we observe the Doppler effect by seeing the lines in its spectrum

redshifted (shifted toward the red end of the light spectrum)

The red and blue spots in images of cosmic microwave background images represent

regions of small over-density and under-density

Astronomers now think that there is a black hole with more than 4 million times the mass of our sun at the center of our Galaxy

about 17 times the size of the Sun

The reciprocal of the Hubble constant (1/Ho) is a rough measure of the

age of the universe

When laser beams in the interferometer combine

an interference pattern of bright and dark light is formed

How fast do radio waves travel?

at the speed of light

Compared to the mass of our own Milky Way Galaxy the total mass we estimate for the Andromeda Galaxy is

somewhat bigger

Our milky way galaxy is what type of galaxy

spiral

The type of galaxy that sometimes has a distinct bar of stars running across the central region is

spiral

The fact that each type of atom has a unique pattern of electron orbits helps explain

that each type of atom shows different absorption or emission spectra

How do astronomers think the amount of detectable matter in the universe compares to the amount of dark matter and dark energy

the amount of detectable matter is far LESS than the amount of dark matter and energy

A type of star that has turned out to be extremely useful for measuring distances is

the cepheid variables

Which of the following is a characteristic of degenerate matter in a white dwarf star?

the electrons get as close to each other as possible and resist further compression

Stars with a larger initial mass

burn faster, so have shorter lifetimes

According to the general theory of relativity, the presence of mass

causes a curvature (or warping) of spacetime

The term multi-messenger astronomy refers to

combining electromagnetic and gravitational wave observations

The reason why big bang nucleosynthesis cannot occur earlier than 1 minute is because

conditions must be sufficiently cool to not disrupt deuterium

If the universe consisted only of matter and its density were equal to critical, the universe would

continue expanding, eventually slowing down to zero

Which of the following is not a prediction of general relativity

dark matter

Current measurements of the Hubble constant Ho

disagree depnding on the method used

A galaxy observed at redshift of z=9 has a prominent hydrogen spectral line. If this same spectral line has a wavelength of 100 nanometers (nm) when observed from hydrogen in a lab on earth, its observed wavelength from the galaxy is

1000nm

The event horizon of a black hole with mass 1 M☉ has a radius of about

3 kilometer

In the current epoch, roughly what percent of mass and energy contents of the universe is made up of ordinary (atomic) matter?

5 percent

Light from the sun takes approximately how long to reach the earth

8 minutes

Roughly what percent of the mass and energy contents of the universe made up of dark matter plus dark energy

95 percent

After traveling 140 million light-years from the 170817 neutron star merger, gravitational waves and gamma rays

arrived at earth at almost exactly the same time

A gravitational lens is formed by

mass between the source and earth

When two light elements collide to undergo nuclear fusion

some of the energy in their mass is released

How fast do electromagnetic waves travel?

speed of light

The main postulate of special relativity is that?

the speed of light is an absolute constant

Evidence for dark matter in astronomy includes galactic rotation curves, interacting galaxy clusters like "bullet cluster"

gravitational lensing by galaxy clusters

The most common element in the sun is

hydrogen

As astronomers have learned more about the structure of the Sun, they have found that it:

is made entirely of hot ionized gas

Time dilation means that

moving clocks run slow

Which part of the Sun has the greatest density

the core

Gravitational wave detectors can locate the position of an astrophysical object like a binary neutron star merger using

the difference in time of arrival of the waves at the different detectors

The equivalence principle (principle of equivalence) says that

the effects of gravity are equivalent to the effects of acceleration

The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe is called.

the event horizon

The redshift observed in the light emitted by distant galaxies is due to

the expansion of space

If a very distant galaxy looks blue overall to astronomers, from this they can conclude that

the galaxy must have a lot of hot, young stars

An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation

the galaxy must have a lot of star formation going on at the time we are seeing it

With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that

the galaxy must have had an entire generation of stars that was born, lived and died

How did observations show that gamma-ray bursts were not coming from the Milky Way Galaxy

the gamma-rays came from all over the ski, not just the plane of the Galaxy

The model of the universe that involves an enormous increase of size during a very short time in the early universe is called

the inflationary universe model

The measurement of cosmic distance was helped tremendously by the discovery, in the early part of the 20th century, that in cepheid variable stars, the average luminosity was related to:

the length of time they took to vary

A student shines a flashlight out the window of a very fast rocket. If the normal speed of light is c, then

the light always travels at speed c

Ninety percent of all-stars (if plotted on an H-R diagram would fall into a region astronomers call:

the main sequence

Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?

the measurement of galaxy distances using type 1a supernova

In the first detection of gravitational waves from LIGO in 2015, the waves came from

the merger of two black holes

The strongest force we know is

the nuclear force which holds nuclei together

A neutron star is as dense as

the nucleus of an atom

In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be:

the same luminosity

In the formula E=mc^2, the letter c stands for

the speed of light

The speed that gravitational waves travel is

the speed of light

In the observation of galaxies, astronomers refer to look back time, which means

the time it took for the observed light to reach us

In a type 1a supernova, the cause of the violent outburst is

the transfer of so much mass from a companion star that a white dwarf produces enormous fusion.

The location of the 170817 neutron star merger was first determined using

three gravitational wave detectors

The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event; they were actually observing

two neutron stars spiraling toward each other merging

Which of the following objects is considered useful to astronomers as a "standard bulb" for determining distances?

type 1a supernova

The elementary particles making up ordinary matter on earth today are

up quark, down quark, electron

In the 2015 gravitational wave discovery event, the two black holes

were each 30 solar masses

Redshift measurements of early galaxies indicate that galaxies and stars had formed

within 500 million years after the big bang

Astronomers have concluded that pulsars are

rotating neutron stars

What is the key reason that gravitational waves are so much harder to detect than electromagnetic (e-m) waves?

Gravitational waves are much weaker than e-m waves and therefore require very, very precise equipment to detect

The most stable (tightly bound) atomic nucleus in the universe is

Iron

Measurements show a certain star has a very high luminosity (100,000 x Sun) while its temperature is quite cool (3500 K) How can this be?

It must be quite large in size

How do astronomers learn what elements are present in a given star?

Look at the absorption lines in its spectrum

To predict whether a star will ultimately become a black hole, what is the key property of a star we should look at?

Mass

Spacetime effects like time dilation are only noticeable when

Objects move close to the speed of light

Einstein suggested that the regular change(advance) in the perihelion of the planet Mercury could only be explain by:

a distortion in spacetime caused by the gravity of the Sun

Which type of galaxy is observed to contain mostly older stars?

elliptical

In the sun, when a positron and an electron collide, they will produce

energy in the form of gamma rays

Gravitation is responsible for the contraction of a main-sequence star, what force opposes this contraction and keeps the star in stable equilibrium?

energy production from fusion in the core

Where in space did the expansion of the universe begin?

everywhere at once

Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is

exactly equal to critical density

After the core of a massive star becomes a neutron star, the rest of the star's material

explodes outward as a supernova

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the

faster it is moving away from us

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

finding the redshift and using Hubble's Law