midterm #2 || astronomy 123 || raymond frey || fall 2019

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

1000 nm (z + 1 x 10)

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

the object created by the merger of two black holes is

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

which of the following is NOT a candidate for the identity of dark matter

anti-matter, MACHOS

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

appear bent when observed from earth

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

arrived at earth at almost the same time

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

as the black hole gets closer, the signal frequency and amplitude increase

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 theory of general 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

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

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 to 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

evidence for dark matter in astronomy includes galactic rotational curves, interacting galaxy clusters like the "bullet cluster", and

gravitational lensing by galaxy clusters

what is the 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 precise equipment to detect

the most prolifically created nuclear species in big bang nuclear synthesis is

helium 4

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

which of the following does NOT happen when two galaxies collide

many of the stars in one galaxy collide with 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 the earth

the core of neutron stars consists of

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

time dilation means that

moving clocks run slow

we now know that the 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

having two LIGO detectors separated by 3000 km is important because

only true astrophysical signals would be observed by both detectors and the time of arrival signals can be used to find the position of the sources

the 17081 event demonstrated that neutron star mergers

produce gamma ray bursts, produce gravitational waves, produce most of the heavy elements on earth, and produce kilonova afterglows

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

when astronauts aboard the ISS in space let go of an orange, it just floats there. why is that?

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

how to astronomers currently thin 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 and energy

the equivalence principle 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

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

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

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

when laser beams in an interferometer combine

the interference pattern of bright and dark light is formed

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

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

the merger of two black holes

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

the first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, what they were observing was

the spiraling toward each other of two neutron stars

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

the time it took for the observed light from the 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, neutrino

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

were each about 30 solar masses