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ast 104 hw from lectures 21-22
Terms in this set (49)
Local forces and local motion are able to overcome the effects of the expansion of the Universe because...
the rate of expansion for small distances is low enough to not matter much.
Arrange the following collections of stars in order from the smallest (1) to the largest (5).
1.open star cluster
An astronomer in the Andromeda Galaxy notices that they are on a collision course with the Milky Way. Worried that we might not know about the inevitable collision, they send us a message in the form of light. If the Andromeda Galaxy is 2.5 million light years away, how long will it be before the signal reaches us?
2.5 million years
If the expansion of the Universe was always constant (so that Hubble's plot of recessional speed vs time was a straight line for all of time) what could we learn directly from the slope of the line?
the age of the Universe
The above plots show possible Hubble Diagrams for different Universes. If the Hubble Parameter hasn't changed with time, which of these plots shows the Hubble Diagram for the oldest Universe?
Today we observe that the Universe is expanding, meaning that galaxies are becoming more spread out and the Universe less dense. This means that, in the past...
galaxies were more bunched up, and the Universe was denser.
Where in the Universe can we find the center point for the expansion of the Universe?
There is no center of the expansion of the Universe.
Why would "The Everywhere Stretch" be a better name for start of the expansion of the Universe, which we call "The Big Bang"? (Select all that apply.)
the expansion happens (and is happening!) everywhere, and the Big Bang makes it sound like an explosion at a particular place.
Nothing is exploding in a "Bang"; it's stretching.
According to the Cosmological Principle...
the laws and large-scale structure of the Universe should be the same everywhere in the Universe; where we are isn't special.
Suppose a galaxy's redshift is measured to be z = 2. According to the graph above, what is the lookback time for this galaxy? In other words, how far back into the past are we seeing when we observe this galaxy?
10 billion years
Which of the following statements comparing the Observable Universe to the Entire Universe are correct? (Select all that apply.)
The Entire Universe doesn't have a spacial edge, but the Observable Universe does.
Both the Universe and the Observable Universe have a temporal edge, i.e. a beginning.
When we survey the most distant galaxies (i.e. those which appear as they did in the most distant past), we find that they must be imaged with an infrared camera. Why?
These galaxies are so distant that their redshifts are all very extreme.
Which of the following statements is true about galaxies in the early Universe? (Select all that apply.)
They tended to be bluer with a lot of active star formation.
Most of the ones we have observed appear to be irregular galaxies.
Compared to today, what was the very early Universe like?
hotter, denser, and smaller
How hot was the very early Universe?
super duper mega ultra extra nearly-impossible-to-describe hot
What effects might gravitational lensing have on the image of a distant galaxy? (Select all that apply.)
The galaxy may appear in a different part of the sky than it actually is.
The galaxy may be magnified, appearing bigger than the original image.
The galaxy may appear in multiple places at once.
If the most distant light in the Universe comes from 13.8 billion light years away, why do we say that the radius of the Observable Universe is nearly 46.5 billion light years?
That distant object has moved since it emitted that light, and today would appear 46.5 billion light years away if light traveled instantly.
When we say that the Universe is expanding, what do we mean?
Space itself is expanding, carrying the objects of the Universe with it.
Based on all of our observations, what do we think is happening to the rate at which our Universe is expanding?
The rate of expansion is accelerating, speeding up with time.
True or false? Our current understanding of physics allows us to predict everything that happened since the Big Bang, including the first few fractions of a second.
We can find how long ago a galaxy was "right on top of us" by dividing that galaxy's distance from us by its recessional speed. If we find this time for many different galaxies, what trend do we discover?
the same time for all galaxies, roughly 13.6 billion years
What is the Cosmic Microwave Background, or CMB?
The radiation that was spread throughout the Universe at the time that it became transparent to light.
The CMB fits almost perfectly to a blackbody curve of an object with a temperature of 2.73K. This means that
The temperature of the early Universe was much hotter than 2.73K, because the radiation has been significantly redshifted since it was emitted.
Why was it important that the CMB is not perfectly uniform everywhere on the sky?
There needed to be deformations in order for galaxies to be seeded in the later Universe.
What is Dark Energy?
the mysterious phenomenon that is causing the rate at which the Universe expands to accelerate in spite of gravity
Why did it take nearly 400,000 years after the Big Bang for atoms to form?
Temperatures were so high that it was nearly impossible for electrons to be trapped by atomic nuclei.
Of the following, which has increased in total amount over time as the Universe has aged? (Select all that apply.)
Which of the following contributes the most to the amount of "stuff" in the universe today?
Arrange the following events from earliest (1) to most recent (13).
the Big Bang occurs
the Milky Way Galaxy forms
our solar system forms and life on Earth begins
Earth's atmosphere becomes oxygenated
the first complex lifeforms appear on Earth
land plants appear
dinosaurs become extinct
humans invent writing systems
modern astronomy is developed
The idea that there is nothing uniquely special about our place in the universe is called the...
When investigating the ability of life to thrive in extreme environments, astrobiologists study... (Select all that apply.)
bacteria in hot springs
organisms growing near deep ocean hydrothermal vents
On how many planets and moons have astrobiologists found life?
Which of the following places in our solar system do astrobiologists believe could potentiallty support life, either currently or in the distant past? (Select all that apply.)
Which of the following types of electromagnetic radiation would enable the fastest interstellar communication because it travels with the greatest speed?
Electromagnetic radiation of all wavelengths travel at the same speed.
In 1974, scientists at the Arecibo Radio Observatory sent a message out into space via a powerful radio signal directed toward globular cluster M 13. Given that this globular cluster is about 22 thousand light-years away, when is the soonest we could hope to receive a reply?
44 thousand years
Why might a civilization capable of sending interstellar radio signals not do so? (Select all that apply.)
There are no civilizations capable of interstellar radio signals besides Earth.
Most civilizations destroy themselves not long after developing this level of technology.
Most civilizations develop a better method of communication not long after developing radio technology.
Which of the following are possible solutions to the Fermi paradox? (Select all that apply.)
It is the nature of intelligent life to destroy itself.
Our current observations are incomplete and we simply have not detected them yet.
If astronomers detect a signal of extraterrestrial origin, they hope to observe three features in order to call it a real candidate for a signal from an extraterrestrial civilization. Which of the three did the 1977 "Wow! Signal" exhibit? (Select all that apply.)
The signal should be broadcast at a wavelength that is universally significant, like a hydrogen emission line.
The signal shouldn't resemble a signal that occurs naturally (like pulsars).
Which of the following is the most likely way we will detect the first sign of extraterrestrial life?
Finding an atmosphere altered by life that exhibits otherwise unlikely chemical signals in its absorption spectrum.
Which of the following are terms in the Drake equation estimating the number of advanced civilizations in our galaxy? (Select all that apply.)
the length of time that a civilization releases detectable signals into space
the fraction of habitable planets on which life develops
the fraction of stars with planets
the fraction of planets on which life can evolve intelligence
What kind of star is typically found at the center of a planetary nebula?
a white dwarf
How is a planetary nebula formed?
a red giant star expells its outer layers
Why does the center of a spiral galaxy typically appear as a bright smear of yellow-white light?
It is a region filled with many old main-sequence stars.
What are the spiral bands that make up the "arms" of a spiral galaxy?
waves of active star formation lighting up hydrogen and dust
Why do the disks of spiral galaxies typically appear so blue?
They're filled with young, hot stars.
Why do elliptical galaxies typically appear so orange-yellow?
They're filled with cool, older main sequence stars.
Of the following, which is the hottest star?
Of the following, which is the smallest star?
Star A and Star B appear near each other on the sky and exhibit almost the same parallax angle. They both appear yellowish-orange but Star A is much brighter in the sky. What can we say about these two stars? (Select all that apply.)
Star A is much larger than Star B.
They may have grown from the same H II region millions of years ago.
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