HW5

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What kinds of objects lie in the halo of our galaxy?

Globular Clusters

What kinds of objects lie in the disk of our galaxy?
A) O and B stars
B) gas and dust
C) open clusters
D) old K and M stars
E) all of the above

E) All of the Above

What makes up the interstellar medium?

Gas and Dust

How does the interstellar medium obscure our view of most of the galaxy?

It absorbs visible, ultraviolet, and some infrared light.

How can we see through the interstellar medium?

by observing high-energy wavelengths such as X Rays and long wavelengths of light such as radio waves

All the iron on Earth originated from

Nuclear Fusion within the cores of High Mass stars

Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?

Halo stars formed in an environment where there were few heavy elements to create rocky planets

What produces the 21-cm line that we use to map out the Milky Way Galaxy?

Atomic Hydrogen

Compared with our sun, most stars in the Halo are

old, red, and dim with few heavier elements

Compared with stars in our disk, orbits of stars in the halo

are elliptical, with random orientation

Approximately how long does it take the sun to orbit the Milky Way Galaxy?

230 Million years

Why do we believe 90 percent of the mass in the Milky Way is in the form of dark matter?

the orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo

Where does most star formation occur in the Milky Way today?

in the spiral arms

What evidence supports the theory that there is a black hole at the center of the Galaxy?

The motions of gas and stars at the center indicate it contains a million solar masses within a region only about 1 parsec across

Based on counting the number of galaxies in a small patch of sky and multiplying the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately

100 billion

Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?

the one that is farthest away

Compared to spiral galaxies, elliptical galaxies are

redder and rounder

The disk component of a spiral galaxy includes which of the following parts?

Spiral Arms

What is the major difference between an elliptical galaxy and a spiral galaxy

an elliptical galaxy lacks a disk component

Which of the following types of galaxies are most commonly found in large clusters?

ellipticals

Which of the following is true about irregular galaxies?

they were more common when the universe was younger

What is a standard candle?

Any object for which for which we are likely to know the true luminosity

Why is the hyades cluster important for building up a catalog of the true luminosities of main-sequence stars

It is close enough to us that the distance to the cluster stars can be found by stellar parallax

How did edwin Hubble measure the distance to the Andromeda Galaxy?

He applied the period-luminosity relation to Cepheid variables

What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

velocity and distance

What is Hubble's Law?

the recession velocity of a galaxy is directly proportional to its distance from us

What makes a white dwarf supernova good standard candles?
A) They are very bright, so they can be used to determine the distances to galaxies billions of light-years
away.
B) They should all have approximately the same luminosity.
C) They occur so frequently that we can use them to measure the distances to virtually all galaxies.
D) We have had several occur close to us in the Milky Way, so we have been able to determine their
luminosities very accurately.
E) both A and B

both A and B

What is the Tully-Fisher relation?
A) The longer the period of a galaxy's variable stars, the more luminous it is.
B) The further away a galaxy is, the faster its recession velocity.
C) The redder a galaxy's color, the further away it is.
D) The smaller a galaxy appears, the further away it is.
E) The faster a spiral galaxy's rotation speed, the more luminous it is.

The faster a spiral galaxy's rotation speed, the more luminous it is

What is the most accurate way to determine the distance to a nearby star?

Stellar parallax

What is the most accurate way yo determine distance to a nearby galaxy?

using Cepheid variables

What is the most accurate way to determine distance to a very distant irregular galaxy?

using a white-dwarf supernova as a standard candle

Which of the following sequences lists the methods for determining distance in the correct order from
nearest to farthest?
A) main-sequence fitting, parallax, Hubble's law, Cepheid variables, white-dwarf supernovae
B) main-sequence fitting, parallax, Cepheid variables, white-dwarf supernovae, Hubble's law
C) parallax, main-sequence fitting, white-dwarf supernovae, Cepheid variables, Hubble's law
D) main-sequence fitting, parallax, Cepheid variables, white-dwarf supernovae, Hubble's law
E) parallax, main-sequence fitting, Cepheid variables, white-dwarf supernovae, Hubble's law

E) Parallax, main-sequence fitting, Cepheid variables, white dwarf supernova, Hubble's Law

Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mpc. Which
statement below automatically follows?

Dr. X believes that the universe is older than Dr. Y believes

Why can't we see past the cosmological horizon?

Beyond the cosmological horizon, we are looking back in time before the universe had formed

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