UO Astronomy 123 Exam 2
If our Sun were to become a black hole, the radius of its event horizon would be about
3 kilometers
Roughly what percent of the mass and energy contents of the universe is made up of ordinary (atomic) matter?
5 percent
Roughly what percent of the mass and energy content of the universe is made up of dark matter plus dark energy?
95 percent
Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these:
Carbon
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
The "horizon problem" is illustrated by what observation of the cosmic microwave background (CMB)?
That the temperature of disconnected regions is almost exactly the same
When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?
Within about a billion years of the present time
Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by:
a distortion in spacetime caused by the gravity of the Sun
The object(s) created by the merger of two black holes is
a single black hole with mass slightly lower than the sum of the merging ones
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
When laser beams in an interferometer combine
an interference pattern of bright and dark light is formed
Which of the following is not a candidate for the identity of dark matter:
anti-matter
General Relativity predicts that light passing near a massive object like the sun will
appear bent when observed from Earth
After travelling 140 million light years from the 170817 neutron star merger, gravitational waves and gamma rays
arrived at earth at almost exactly the same time
Why do widely separated galaxies move apart? (Why do we have Hubble's law)?
as a result of the big bang, space itself is stretching, and this stretching carries the galaxies away from each other
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 dark matter is FALSE:
astronomers have a pretty good idea what the dark matter is made of
The three observational pillars of cosmology are the expanding universe, the cosmic microwave background, and
big bang nucleosynthesis
According to the general theory of relativity, the presence of mass
causes a curvature (or warping) of spacetime
If the universe consisted only of matter and its density were equal to critical, the universe would
continue expanding, eventually slowing down to zero
When the age of the universe was about 10 seconds, it had cooled sufficiently for neutrons and protons to bind together and form the key nuclear species which allows production of helium to proceed. This key nucleus is called
deuterium
Current measurements of the Hubble constant H0
disagree depending on the method used
Where in space did the expansion of the universe begin?
everywhere at once
Based on cosmic microwave background (CMB) data, astronomers now conclude that the average density of the universe is
exactly equal to critical density
Astronomers now conclude that the average density of the universe is
exactly equal to the critical density
Measurements of the cosmic microwave background provide strong evidence that the overall geometry of space is
flat, or zero curvature
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
What is a key reason that gravitational waves are so much harder to detect than electromagnetic waves?
gravitational waves are much weaker than electromagnetic waves, and therefore require very, very precise equipment to detect
According to the Cosmological Principle, the universe
is isotropic and homogeneous over large distances
After a star collapses to form a black hole, the only information we can measure is
its mass, spin, and electric charge
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
To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?
mass
A gravitational lens is formed by
mass between the source and earth
We now know that most heavy elements such as gold are produced in
neutron star mergers
Special relativity gives a "speed limit", meaning that
objects cannot move faster than the speed of light
Spacetime effects like time dilation are only noticeable when
objects move close to the speed of light
Modern particle accelerators are able to recreate some conditions of the early universe because
of the high energy of the particles in the beams
Merging black holes can be observed
only by their gravitational wave emission
The 170817 event demonstrated that neutron star mergers
produce gamma ray burstsb. produce gravitational wavesc. produce most of the heavy elements on earthd. produce kilonova afterglowse. all of the above
Protons and neutrons are composed of other more elementary particles known as
quarks
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:
redder and smaller
Which of the following did NOT happen during the first few minutes after the Big Bang?
some very massive early stars formed
The speed that gravitational waves travel is
speed of light
Why do galaxies collide, while stars almost never do?
stars are very far apart compared to how big they are
When scientists say that "black holes have no hair", what do they mean?
that once a black hole forms, very little information can be extracted from it about the material that is now inside
The "horizon problem" is illustrated by what observation of the cosmic microwave background (CMB)?
that the temperature of disconnected regions is almost exactly the same
When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that?
the ISS is falling around the Earth, and in free fall, things feel no weight
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter?
the amount of detectable matter is about 1/5th the amount of dark matter
The image below represents a measurement of what?
the cosmic microwave background
The three observational pillars of cosmology are the expanding universe, big bang nucleosyntheses, and
the cosmic microwave background
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
Which of the following does not represent evidence for dark matter?
the fusion of hydrogen in stellar cores
An astronomer is observing a distant galaxy at lookback time of 11 BY 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
A very distant galaxy at lookback time 5 billion years looks blue overall to astronomers, from this they can conclude that:
the galaxy must have a lot of young stars and thus active star formation must still be going in 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
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
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
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 Ia supernovae
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from
the merger of two black holes
The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, what they were observing was:
the merger of two neutron stars
Observations of the spectra of the afterglow of the binary neutron star merger revealed
the presence of newly created heavy elements
Which of the following does not represent evidence for dark matter?
the rate of cosmic ray showers
In measuring the speed of stars orbiting on the outer edge of a galaxy, the expectation without dark matter is that
the speed decreases as the star is further from the galactic center
The main postulate of special relativity is that
the speed of light is an absolute constant
In the observation of galaxies, astronomers refer to look-back time, which means
the time it took for the observed light from a galaxy to reach us
What happened when the age of the universe was 380,000 years which allows us to observe the cosmic microwave background?
the universe cooled sufficiently to allow neutral hydrogen to form
The reason nucleosynthesis stopped when the age of the universe was about 3 minutes was
the universe was cooling too fast to produce elements beyond helium
The observed cosmic microwave background (CMB) is extremely uniform. What is the significance of the small deviations from uniformity which show up as red or blue regions in the CMB images?
they seed the large scale structure we observe today
The location of the 170817 neutron star merger was first determined using
three gravitational wave detectors
According to General Relativity, in a freely falling reference frame, light
travels in a straight line
For the first generation of stars formed in the early universe, their composition
was almost entirely hydrogen
In the 2015 gravitational wave discovery event, the two black holes
were each about 30 solar masses
