Final Flashcards
(33 cards)
How do we observe the life histories of galaxies?
Deep observations of the universe show us the history of galaxies because we are seeing galaxies as they were at different ages.
How do we study galaxy formation?
Our best models for galaxy formation assume that gravity made galaxies out of regions in the early universe that were slightly denser than their surroundings.
Why do galaxies differ?
Some of the differences between galaxies may arise from the conditions in their protogalactic clouds (e.g. competition between angular momentum and mass density).
Collisions can play a major role because they can transform two spiral galaxies into an elliptical galaxy, or they can induce spiral arms.
What are starbursts?
A starburst galaxy is transforming its gas into stars much more rapidly than a normal galaxy. Starburst epochs likely last only a few million to a few ten million years.
What are quasars?
Active galactic nuclei are very bright objects seen in the centers of some galaxies, and quasars are the most luminous type.
What is the power source for quasars and other active galactic nuclei?
The only model that adequately explains the observations holds that the central engines (or power sources) of AGNs consist of mass falling into supermassive black holes
Do supermassive black holes really exist?
Observations of stars and gas clouds orbiting at the centers of galaxies indicate that many galaxies, and perhaps all of them, have supermassive black holes.
How do quasars let us study gas between the galaxies?
Absorption lines in the spectra of quasars tell us about intergalactic clouds between those quasars and Earth.
What were conditions like in the early universe?
The early universe was so hot and so dense that radiation was constantly producing particle–antiparticle pairs and vice versa.
How did the early universe change with time?
As the universe cooled, particle production stopped, leaving matter instead of antimatter.
Fusion turned remaining neutrons into helium.
Radiation traveled freely after formation of atom
How do observations of the cosmic microwave background support the Big Bang theory?
Radiation left over from the Big Bang is now in the form of microwaves – the cosmic microwave background – which we can observe with a radio telescope.
How do the abundances of elements support the Big Bang theory?
Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory.
What key features of the universe are explained by inflation?
The origin of structure, the smoothness of the universe on large scales, the nearly critical density of the universe.
Structure comes from inflated quantum ripples.
Observable universe became smooth before inflation, when it was very tiny.
Inflation flattened the curvature of space, bringing expansion rate into balance with the overall density of mass-energy.
Why is the darkness of the night sky evidence for the Big Bang?
If the universe were eternal, unchanging, and everywhere the same, the entire night sky would be covered with stars.
The night sky is dark because we can see back to a time when there were no stars.
Stated more scientifically: The night sky is dark because we can only see a finite part in a universe of finite age – there is a horizon in a universe of finite age. Furthermore, the light of distant stars is redshifted beyond visibility due to the expansion of the universe.
What do we mean by dark matter and dark energy?
Dark matter is the name given to not “directly” visible mass whose gravity governs the observed motions of stars and gas clouds.
Dark energy is the name given to whatever might be causing the expansion of the universe to accelerate.
What is the evidence for dark matter in galaxies?
Rotation curves of galaxies are flat, indicating that most of their matter lies outside their visible regions.
What is the evidence for dark matter in clusters of galaxies?
Masses measured from galaxy motions, temperature of hot gas, and gravitational lensing all indicate that the vast majority of matter in clusters is dark.
Does dark matter really exist?
Either dark matter exists or our understanding of gravity must be revised.
What might dark matter be made of?
There does not seem to be enough normal (baryonic) matter to account for all the dark matter, so most astronomers and physicists suspect that dark matter is made of (non-baryonic) particles that have not yet been observed in particle physics labs.
Why is Dark Matter critical for Structure Formation?
Overdense regions needed to form and start growing before the universe was 380,000 years old to explain the large scale structure seen today.
Ordinary matter was prevented by radiation to form clumps before the universe was 380,000 years old.
Dark matter does not interact with radiation and could start to form clumps already a few thousand years after the Big Bang.
What is the role of dark matter in galaxy formation?
The gravity of dark matter seems to be what drew gas together into protogalactic clouds, initiating the process of galaxy formation.
WIMP dark matter can also start to form clumps before ordinary matter could form clumps.
What are the largest structures in the universe?
Galaxies appear to be distributed in gigantic chains and sheets that surround great voids.
The largest confirmed structures (like the Sloan Great Wall) have a size of order of a billion light years, and likely there are no larger structures than that (the astronomical “End of Greatness”).
Will the universe continue to expand forever?
Current measurements indicate that there is not enough dark matter to prevent the universe from expanding forever.
Is the expansion of the universe accelerating?
An accelerating universe is the best explanation for the distances we measure when using white dwarf supernovae as standard candles.
A large amount of uniformly distributed energy (about 69% of the total energy density in the universe) can explain the observed acceleration of cosmic expansion. This uniformly distributed form of energy is denoted as Dark Energy.
