CP 23 Dark Matter, Dark Energy, and the Fate of the Universe Flashcards
Dark matter is inferred to exist because:
we can observe its gravitational influence on visible matter.
Why do we call dark matter “dark”?
It emits no radiation that we have been able to detect.
Dark energy has been hypothesized to exist in order to explain:
observations suggesting that the expansion of the universe is accelerating.
When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean?
It bends or distorts the light coming from galaxies located behind it.
What is the distinguishing characteristic of what we call ordinary (or baryonic) matter?
It consists of atoms or ions with nuclei made from protons and neutrons.
Strong evidence for the existence of dark matter comes from observations of:
clusters of galaxies.
Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies?
subatomic particles that we have not yet detected in particle physics experiments
What is the primary way in which we determine the mass distribution of a spiral galaxy?
We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy’s center.
Which of the following best summarizes what we mean by dark energy?
It is a name given to whatever is causing the expansion of the universe to accelerate with time.
How does gravitational lensing tell us about the mass of a galaxy cluster?
Using Einstein’s theory of relativity, we can calculate the cluster’s mass from the way in which it distorts the light of galaxies behind it.
What do we mean when we say that the rotation curve for the Milky Way Galaxy is “flat”?
Gas clouds orbiting far from the galactic center have approximately the same orbital speed as gas clouds located further inward.
Measuring the amount of deuterium in the universe allows us to set a limit on __________.
the density of ordinary (baryonic) matter the universe
When we speak of the large-scale structure of the universe, we mean __________.
the overall arrangement of galaxies, clusters of galaxies, and superclusters in the universe
Based on evidence from measurements of the acceleration of the expansion rate and from careful study of the cosmic microwave background, about what percentage of the universe’s total mass and energy takes the form of ordinary atomic matter (protons, neutrons, and electrons)?
5%
The primary observation that has led astronomers to conclude that the expansion of the universe is accelerating comes from __________.
observations of white dwarf supernovae
Based on current evidence, a supercluster is most likely to have formed in regions of space where _________.
the density of dark matter was slightly higher than average when the universe was very young
Is space expanding within clusters of galaxies? Why or why not?
No, because their gravity is strong enough to hold them together even while the universe as a whole expands.
Which model presumes the existence of some type of dark energy in the universe
accelerating universe
Which of the following possible types of universe would not expand forever?
a recollapsing universe
Based on current evidence, how does the actual average density of matter in the universe compare to the critical density?
The actual average density of matter, even with dark matter included, is only about a quarter of the critical density.
Which statement best describes current understanding of the eventual fate of the universe?
Although the accelerating expansion suggests that the universe will continue to expand forever, it is possible that future discoveries will indicate a different fate.
Hubble’s constant is related to the age of the universe, but the precise relationship depends on the way in which the expansion rate changes with time. For a given value of Hubble’s constant (such as 22 km/s/Mly), the age of the universe is oldest if in which universe
critical
recollapsing
accellerating
coasting
Accellerating
