astronomy 1020 – Flashcards
Unlock all answers in this set
Unlock answersquestion
How do observations of distant galaxies help us learn about galaxy evolution?
answer
Observations at different distances show galaxies of different ages and therefore different stages of evolution.
question
I observe a galaxy that is 100 million light-years away: what do I see?
answer
the light from the galaxy as it was 100 million years ago and it is redshifted
question
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
answer
a dense cloud with very little angular momentum
question
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
answer
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.
question
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
answer
3 m.
question
Why should galaxy collisions have been more common in the past than they are today?
answer
Galaxies were closer together in the past because the universe was smaller.
question
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
answer
the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies *all of the above*
question
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
answer
determining their redshifts.
question
What is a quasar?
answer
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
question
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
answer
They are more common at very great distances.
question
Which of the following cannot be true of the very first stars formed in the Universe?
answer
They are more common at very great distances.
question
Which of the following cannot be true of the very first stars formed in the Universe?
answer
They may have had rocky planets around them.
question
How do we know that there are intergalactic clouds between a distant quasar and us?
answer
We see hydrogen absorption lines at redshifts smaller than that of the quasar.
question
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
answer
by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
question
starburst galaxies
answer
have highest rate of star formation
question
central dominant galaxies
answer
largest individual galaxies in the universe
question
galactic winds
answer
many supernova events in a relatively small volume of a galaxy
question
most luminous objects on the universe
answer
qusars
question
energy for all active galactic nuclie comes from
answer
supermassive black hole
question
characterized by sources of large energy
answer
radio galaxies
question
Imagine that the Sun gained mass without changing its radius. How would the structure of spacetime change at the distance of Earth's orbit?
answer
Spacetime would become more curved at Earth's orbit.
question
Einstein's general theory of relativity predicts that two orbiting neutron stars should radiate gravitational waves. How does the fact that the orbital period is getting shorter support this prediction?
answer
Gravitational waves must carry some energy away from the system, and this loss of energy must cause the orbits to get smaller over time.
question
What happens when a particle of matter meets its corresponding antiparticle of antimatter?
answer
The combined mass of the two particles is completely transformed into energy (photons).
question
four fundamental forces. Rank these forces from left to right based on their relative strengths between two protons located within the nucleus of an atom, from weakest to strongest.
answer
gravity, weak, electromagnetic, strong
question
Following are the four fundamental forces. Rank these forces from left to right based on their relative strengths between two protons separated by a few centimeters, from weakest to strongest. If you think two (or more) forces have equal strength (or essentially zero strength) in this case, show the equality by dragging one on top of the other(s).
answer
strong and weak, gravity, electromagnetic
question
Following are the four fundamental forces. Rank these forces from left to right based on their relative strengths acting between Earth and the Sun, from weakest to strongest. If you think two (or more) forces have equal strength (or essentially zero strength) in this case, show the equality by dragging one on top of the other(s).
answer
strong and weak, electromagnetic, gravity
question
fundamental force: gravity
answer
weakest force across small distance governs large scale structure of universe
question
fundamental force: electromagnetic
answer
transmitted by photons affetcs only electriclly charged particles
question
fundamental force: strong
answer
holds nuclei tigether transmitted by gluons
question
fundamental force: weak
answer
governs nuclear fission and radio decay
question
Which of the forces are unimportant on large scales because they can be felt only across distances about the size of atomic nuclei or smaller?
answer
small force weak force
question
The electromagnetic force is much stronger than gravity over short distance scales. So why doesn't it dominate over gravity for large masses, such as planets, stars, and galaxies?
answer
The electromagnetic force is much stronger than gravity over short distance scales. So why doesn't it dominate over gravity for large masses, such as planets, stars, and galaxies?
question
How does the existence of helium nuclei (with 2 protons and 2 neutrons) demonstrate that there must be a force in nature that is stronger than the electromagnetic force?
answer
The electromagnetic force makes protons repel, so there must be a stronger force that keeps them together.
question
Degeneracy pressure occurs as a result of a combination of the uncertainty principle and the exclusion principle. This pressure play an important role in the astronomical objects known as __________.
answer
brown dwarfs, white dwarfs, and neutron stars
question
The idea that space can contain virtual particles has been verified in laboratory experiments. In astronomy, this idea is used to predict that black holes __________.
answer
can "evaporate" over time, even though nothing escapes from inside a black hole's event horizon
question
Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that __________.
answer
the universe began very hot and dense and has been cooling as it expands
question
Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits __________.
answer
tiny temperature variations in different directions
question
The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?
answer
Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.
question
eras history of the universe
answer
plank, gut, electroweak, particle nucleo sythesis, nuclie, atoms, galaxy
question
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
answer
Most matter in the early universe was annihilated by antimatter.
question
Which of the following important events occurred earliest in the history of the universe?
answer
Spacetime rapidly expanded during a brief period of inflation.
question
During the history of the universe, what important event occurred about 380,000 years after the Big Bang?
answer
Light began to travel freely through the universe.
question
Essentially all the hydrogen nuclei that will ever exist in our universe was created __________.
answer
by the time the universe was about 3 minutes old
question
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.
answer
fainter and has most of its photons at longer wavelengths
question
To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as ________ after the Big Bang.
answer
10-10 second
question
How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe?
answer
10-43 second
question
Why can't current theories describe what happened during the Planck era?
answer
We do not yet have a theory that links quantum mechanics and general relativity.
question
Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious?
answer
The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.
question
Helium originates from
answer
mostly from the Big Bang with a small contribution from stellar nucleosynthesis.
question
Measuring the amount of deuterium in the universe allows us to set a limit on
answer
the density of ordinary (baryonic) matter in the universe.
question
Based on current evidence concerning the amount of deuterium in the universe, we can conclude that
answer
the density of ordinary (baryonic) matter is between 1 percent and 10 percent of the critical density.
question
What are the two key observational facts that led to widespread acceptance of the Big Bang model?
answer
the cosmic background radiation and the high helium content of the universe
