astronomy 1020

How do observations of distant galaxies help us learn about galaxy evolution?
Observations at different distances show galaxies of different ages and therefore different stages of evolution.
I observe a galaxy that is 100 million light-years away: what do I see?
the light from the galaxy as it was 100 million years ago and it is redshifted
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
a dense cloud with very little angular momentum
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Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.
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
3 m.
Why should galaxy collisions have been more common in the past than they are today?
Galaxies were closer together in the past because the universe was smaller.
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
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*

In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
determining their redshifts.
What is a quasar?
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
They are more common at very great distances.
Which of the following cannot be true of the very first stars formed in the Universe?
They are more common at very great distances.
Which of the following cannot be true of the very first stars formed in the Universe?
They may have had rocky planets around them.
How do we know that there are intergalactic clouds between a distant quasar and us?
We see hydrogen absorption lines at redshifts smaller than that of the quasar.
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
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
starburst galaxies
have highest rate of star formation
central dominant galaxies
largest individual galaxies in the universe
galactic winds
many supernova events in a relatively small volume of a galaxy
most luminous objects on the universe
qusars
energy for all active galactic nuclie comes from
supermassive black hole
characterized by sources of large energy
radio galaxies
Imagine that the Sun gained mass without changing its radius. How would the structure of spacetime change at the distance of Earth’s orbit?
Spacetime would become more curved at Earth’s orbit.
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?
Gravitational waves must carry some energy away from the system, and this loss of energy must cause the orbits to get smaller over time.
What happens when a particle of matter meets its corresponding antiparticle of antimatter?
The combined mass of the two particles is completely transformed into energy (photons).
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.
gravity, weak, electromagnetic, strong
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).
strong and weak, gravity, electromagnetic
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).
strong and weak, electromagnetic, gravity
fundamental force: gravity
weakest force across small distance

governs large scale structure of universe

fundamental force: electromagnetic
transmitted by photons

affetcs only electriclly charged particles

fundamental force: strong
holds nuclei tigether

transmitted by gluons

fundamental force: weak
governs nuclear fission and radio decay
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?
small force weak force
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?
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?
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?
The electromagnetic force makes protons repel, so there must be a stronger force that keeps them together.
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 __________.
brown dwarfs, white dwarfs, and neutron stars
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 __________.
can “evaporate” over time, even though nothing escapes from inside a black hole’s event horizon
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 __________.
the universe began very hot and dense and has been cooling as it expands
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 __________.
tiny temperature variations in different directions
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?
Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.
eras history of the universe
plank, gut, electroweak, particle nucleo sythesis, nuclie, atoms, galaxy
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
Most matter in the early universe was annihilated by antimatter.
Which of the following important events occurred earliest in the history of the universe?
Spacetime rapidly expanded during a brief period of inflation.
During the history of the universe, what important event occurred about 380,000 years after the Big Bang?
Light began to travel freely through the universe.
Essentially all the hydrogen nuclei that will ever exist in our universe was created __________.
by the time the universe was about 3 minutes old
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.
fainter and has most of its photons at longer wavelengths
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.
10-10 second
How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe?
10-43 second
Why can’t current theories describe what happened during the Planck era?
We do not yet have a theory that links quantum mechanics and general relativity.
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?
The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.
Helium originates from
mostly from the Big Bang with a small contribution from stellar nucleosynthesis.
Measuring the amount of deuterium in the universe allows us to set a limit on
the density of ordinary (baryonic) matter in the universe.
Based on current evidence concerning the amount of deuterium in the universe, we can conclude that
the density of ordinary (baryonic) matter is between 1 percent and 10 percent of the critical density.
What are the two key observational facts that led to widespread acceptance of the Big Bang model?
the cosmic background radiation and the high helium content of the universe

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