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