uo astronomy 123 midterm #2
what are the three foundations for big bang cosmology?
(i) the cosmological redshift (Hubble flow) (ii) big bang nucleosynthesis (iii) the cosmic microwave background These were all predictions which were confirmed in great detail.
what are consequences of special relativity?
-Time dilation-for example, allowing cosmic ray muons to reach the surface of the earth -A speed limit: nothing can have speed exceeding the speed of light, c -E=mc^2
Which of the following is not a candidate for the identity of dark matter:
-anti-matter -MACHOs
Having two LIGO detectors separated by 3000 km is important because
-only true astrophysical signals would be observed in both detectors -the time of arrival of signals can be used to find the position of the sources
consequences of general relativity
-perihelion advance of Mercury -gravitational redshift of light -bending and lensing of light -black holes -gravitational waves -the overall evolution and expansion history of the universe
The 170817 event demonstrated that neutron star mergers
-produce gamma ray bursts -produce gravitational waves -produce most of the heavy elements on earth -produce kilonova afterglows
A galaxy observed at redshift of z=9 has a prominent hydrogen spectral line. If this same spectral line has a wavelength of 100 nanometer (nm) when observed from hydrogen in a lab on earth, its observed wavelength from the galaxy is
1000 nm
what does a black hole with a mass of 1m have a horizon radius of?
3 km
we believe that there is about ______ times more dark matter in the universe than ordinary, visible matter.
5
What are gravitational waves?
Ripples in spacetime caused by the acceleration of masses e.g. core collapse of a massive star
due to the energy emitted in GWs...
The merger resulted in single black hole of mass about 3M☉ less than the sum of the merging black holes
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
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 hundred thousand years
what can mergers of binary systems of black holes or neutron stars produce?
a gravitational wave "chirp" signal sufficiently energetic to be detected by the sensitive LIGO detectors.
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
what is the event horizon of the black hole at the center of the Milky Way (4.5 millionM)?
about 17 times the radius of the sun
When laser beams in an interferometer combine
an interference pattern of bright and dark light is formed
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
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
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
why are large redshifts, larger than 1, possible?
because it is space itself which is expanding, not because of galaxies moving faster than the speed of light in a static space.
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
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
Current measurements of the Hubble constant H0
disagree depending on the method used
what will a star with an initial mass of 40m do?
end their life as black holes with masses of about 5M☉ or greater
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
Supermassive black holes form in the early stages of galaxy formation and have masses...
exceeding 1 million M☉
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 usually 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)
what does evidence for dark matter include?
galactic rotation curves, gravitational lensing, and merging galaxy clusters.
what did hubble observed?
galaxies are red shifted, and the greater their distance, the greater the redshift and hence the greater the velocity of recession.
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--something like the structure one would see taking a cross-section of some soap bubbles
Evidence for dark matter in astronomy includes galactic rotation curves, interacting galaxy clusters like the "bullet cluster", and
gravitational lensing by galaxy clusters
What is a 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
what is general relativity?
gravity is caused by the curvature of space
The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, what they were observing was:
he spiraling toward each other of two neutron stars
Gravitational lensing is now used as a tool in astronomy because...
he strength of the lens, for example a cluster of galaxies, is given by its total mass; the lensing images can take the form of multiple images or arcs
The most prolifically created nuclear species in big bang nucleosynthesis is
helium 4,^4He
when was the merger of a binary neutron star system detected?
in 2017 with detection of GWs, accompanied by a gamma-ray burst and a visible kilonova afterglow.
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
According to the Cosmological Principle, the universe
is isotropic and homogeneous
according to the Cosmological Principle, the universe
is isotropic and homogeneous
as the universe rapidly expanded, what did it do?
it cooled, which meant some forms of matter, such as nuclei or atoms, could form and not be pulled apart.
what does cosmological principle say?
it looks similar in all directions. Using this, images like the Hubble deep field find a few 100 billion galaxies in its view.
what does the cosmological principle say about the universe?
it looks similar in all directions. Using this, images like the Hubble deep field find a few 100 billion galaxies in its view.
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
The core of neutron stars consists of
matter with super-nuclear density in a form we don't know for sure
what's the composition of newborn stars?
mostly hydrogen
Time dilation means that
moving clocks run slow
We now know that most heavy elements such as gold are produced in
neutron star mergers
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
Spacetime effects like time dilation are only noticeable when
objects move close to the speed of light
Merging black holes can be observed
only by their gravitational wave emission
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:
redder and smaller
The red and blue spots in images of the cosmic microwave background images represent
regions of small over-density and under-density
the regions of over-density were...
seeds for accumulating matter, which became regions with clusters of galaxies. Similarly, regions of under-density became regions of voids in today's distribution of galaxies.
early galaxies are typically...
smaller, more irregular, and appear redder due to the redshift. Due to frequent galactic mergers in the earlier universe, later galaxies tend to be larger than the early ones.
what does the age of the universe (13.8 billion years) imply?
that early galaxies and stars were formed after only about 500 million years.
what do the large redshifts of distant galaxies mean?
that much of its light is shifted from the UV or visible into the infrared part of the spectrum. The observed redshifts are given by the earth wavelength multiplied by z+1, where z is the redshift.
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 and dark energy?
the amount of detectable matter is far less than the amount of dark matter & energy
The three pillars of evidence for big bang cosmology are the cosmological redshift, big bang nucleosynthesis, and
the cosmic microwave background
what does the event horizon (size) of a black hole represent?
the distance (radius) from the center of black hole within which nothing can escape, including light.
The equivalence principle (principle of equivalence) says that
the effects of gravity are equivalent to the effects of acceleration
Cosmic Microwave Background (CMB)
the electromagnetic radiation left over from the formation of the universe
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
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
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
Once a black hole forms, the size of its event horizon is determined only by
the mass inside the event horizon
what is the horizon radius proportional to?
the mass of a black hole
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from
the merger of two black holes
what did the merger result in?
the production of heavy elements
The speed that gravitational waves travel is
the speed of light
the main postulate of special relativity is that
the speed of light is an absolute constant
what did einstein's special relativity hypothesize?
the speed of light, c, is an absolute constant, which is the same independent of the motion of source or observer.
What is look-back time?
the time it takes for the light from an object to reach Earth
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
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
The location of the 170817 neutron star merger was first determined using
three gravitational wave detectors
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 about 30 solar masses
in the 2015 gravitational wave discovery event, the two black holes
were each about 30 solar masses
