question

which part of the galaxy contains the coldest gas?

answer

the disk

question

what part of the galaxy has gas with the hottest average temperature

answer

the halo

question

What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the Sun?

answer

2%

question

Where would you be most likely to find an ionization nebula?

answer

the disk

question

The best measurements of the mass of the black hole at the galactic center come from

answer

the orbits of stars in the galactic center

question

Where are most of the Milky Way's globular clusters found?

answer

in the halo

question

How do we determine the Milky Way's mass outside the Sun's orbit?

answer

from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun

question

Where would you least expect to find an ionization nebula?

answer

in the halo

question

Which kind of star is most likely to be part of the spheroidal population?

answer

an M star

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, because subsequent fusion in stars has consumed some of this hydrogen but has not made any more.

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

Order of Eras

answer

1. Planck 2. GUT 3. Electroweak 4. particle 5. era of nucleosynthesis 6. era of nuclei 7. era of atoms 8. era of galaxies

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

How do we determine the conditions that existed in the very early universe?

answer

We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.

question

Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang

answer

These two forces first became distinct at this time.

question

According to the Big Bang theory, how many forces - and which ones - operated in the universe during the GUT era?

answer

2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces

question

Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies _____

answer

the electromagnetic and weak forces into the electroweak force

question

What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?

answer

The basic chemical composition of the universe had been determined. After this point, the density and temperature were too low to allow for any more fusion, so no new elements could be created (until stars began to do fusion much later on, but fusion in stars has changed the overall chemical composition only by about 2%).

question

According to the Big Bang theory, why do we live in a universe that is made of almost entirely of matter rather than antimatter?

answer

During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles. The excess was only about 1 extra matter particle for every billion particles of matter and antimatter, and the annihilation of the rest of the billion explains why there are so many photons in the universe.

question

In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?

answer

Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. Until about 380,000 years into the history of the universe, hydrogen atoms were ionized and photons would scatter off electrons before they could travel very far; the universe was opaque.

question

If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for _____

answer

how galaxies came to exist Recall that models of galaxy formation presume that they formed from "seeds" of excess density present in the early universe. If the seeds really existed, they should have left their mark as slight variations in the cosmic microwave background, and we do indeed see such variations. Thus, if we did not see the variations, we would have been forced to reconsider everything we thought we knew about galaxy formation and the history of the universe.

question

In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe?

answer

By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. Temperatures at early times were far higher than this, but there was no helium around at those times.

question

How does the idea of inflation account for the existence of the "seeds" of density from which galaxies and other large structures formed?

answer

Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure.

question

Suppose that inflation did not occur. In that case, the fact that the cosmic microwave background has the same temperature in opposite directions of the sky would be considered _______

answer

surprising, because those locations would never have been close enough to have any light or matter exchanged between them In fact, with inflation, the quantum fluctuations lead to small differences in density and temperature. Without inflation, they would have no effect.

question

Which analogy best explains why inflation predicts that the overall geometry of the observable universe should appear to be flat?

answer

Earth is so big that it the part explored by an ant appears flat.

question

Suppose that the universe were infinite in both extent and age. In that case, we would expect the night sky to be ______

answer

uniformly bright

question

The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation below (these are not real observations) would call our current theory into question?

answer

The discovery of a galaxy with a helium abundance of only 10% by mass.

question

diameter of earth

answer

8000 miles

question

moons distance

answer

60 radii(240,000 mi)

question

distance earth to sun

answer

93 mil miles

question

1 pc

answer

3.26 light years

question

milky way diameter

answer

75000 light years

Ch17 – Astronomy final – Flashcards

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