exam 3
pdf
keyboard_arrow_up
School
Binghamton University *
*We aren’t endorsed by this school
Course
114
Subject
Astronomy
Date
Jan 9, 2024
Type
Pages
4
Uploaded by DukeFire12625
1) The rotation curve of the Milky Way suggests that the majority of the mass of the Milky Way
lies farther out than the Sun's orbit. True
2) The Hertzsprung-Russell Diagram plots ________ against the spectral type or temperature.
E) luminosity or absolute magnitude
3) Shapley found that globular clusters are only found in the Galactic bulge. B) False
4) While examining the spectrum of a galaxy you find all the hydrogen lines are shifted to longer
wavelengths. This galaxy is moving away from us.
5) The rest wavelength of the Balmer blue/green line for Hydrogen has a wavelength of 486 nm.
If a particular galaxy has a recessional velocity that is 15% the speed of light, what is the rest
wavelength of the observed spectral line? B) 559 nm
6) For our Sun, the production of carbon will be the end of its nucleosynthesis. A) True
7) What is the typical main sequence lifetime of a M-type star having a mass of 0.21 Solar
Masses? A) a trillion years
8) A star (no matter what its mass) spends most of its life: E) as a main sequence star.
9) The following diagram shows how a Cephied varaible varies in brightness. Determine the
period of time for one complete cycle of change in brightness. C) 5 days
10) The diagram shows the rotation curve for the Milky Way. The location of the Sun is shown.
Estimating the orbital velocity and radius of the Sun from the graph, determine the estimated
mass of the galaxy contained within the Suns orbital radius. HINT 1: You will need to convert
the speed to m/s and the distance to meters. 1 km/s = 1000 m/s. 1 ly = 9.46 x 1015m. HINT 2,
when you determine the mass in kg, you need to divide by the mass of the Sun to report in
Solar Masses. The mass of the Sun = 2 x 1030kg. B) 1 x 1011 Msun
11) As a star begins to evolve away from the main sequence, it gets larger. A) True
12) The diagram shows the light curve for Delta Cephei, the first variable star to be discovered.
Estimate the luminosity of this varaible star compared to the Sun.C) 103 Lsun
13) Because they all involve the detonation of a carbon-rich white dwarf at Chandrasekhar's
limit, all type I supernovae are equally luminous and hence are excellent standard candles.
A) True
14) The escape speed for a black hole's event horizon is the speed of light. A) True
15) The Milky Way is simply our edge-on view of our home Galaxy. A) True
16) The following light curve is for a variable star. Determine the distance to the star if the
average apparent magnitude is m = 3.75 D) 224 pc
17) Dr. Smith believes that the Hubble constant is H0 = 70 km/s/Mpc. Dr. Jones believes it is H0
= 50km/s/Mpc. Which statement below automatically follows?
D) Dr. Smith believes that the universe is younger than Dr. Jones believes.
18) The brightest stars in a young open cluster will be C) massive blue stars at the top left on
the H-R diagram.
19) According to the Hubble Law graph shown, a galaxy cluster with a recessionalvelocity of
25,000 km/s will be C) 400 million pcs away.
20) It was the distribution of ________ that showed Harlow Shapley we were no where near the
center of the Milky Way in the 1920s. A) globular clusters
21) Except for hydrogen and most of the helium, all the elements have been formed through
stellar nucleosynthesis. A) True
22) The "helium flash" occurs at what stage in stellar evolution? D) red giant
23) A star is on the horizontal branch of the H-R diagram. Which statement is true?
C) It is burning both hydrogen and helium.
24) Refer to the figure above. What is the name of the path between the points labeled 11 and
12? D) planetary nebula
25) A high-mass star dies more violently than a low-mass star because: C) it generates more
heat and its core eventually collapses very suddenly.
26) What characteristic of a star cluster is used to determine its age? A) the main sequence
turnoff
27) Mass transfer in binaries occurs when one giant swells to reach the A) Roche Lobe.
28) Two important properties of young neutron stars are E)extremely rapid rotation and a strong
magnetic field.
29) What would happen if mass is added to a 1.4 solar mass white dwarf?
C) The star would erupt as a carbon detonation (type I) supernova.
30) Neutron stars do not have D) rotation periods comparable to the Sun's.
31) Which of the following can actually escape from inside a black hole's event horizon?
D) none of the above
32) The Schwartzschild radius for a 12 solar mass star is A) 36 km.
33) If the Sun were replaced by a one solar mass black hole
B) we would still orbit it in a period of one year.
34) Henrietta Leavitt first showed the relationship between the mass and luminosity of Cepheids
and their period of pulsation; the brighter, the longer this period. A) True
35) The majority of the mass of the Milky Way lies farther out than the Sun's orbit. A) True
36) Which is the correct description of the Sun's location within the Milky Way?
A) in the disc and about one-half a galactic radius from the center
37) Which of the following is most like the rotation of stars in the disk of the Milky Way?
B) cars moving at a constant speed on a circular race track
38) Using an orbit size of 8 kpc, and a period of 225 million years, the mass of our Galaxy is
found to be closest to (hint: convert radius to meters and time seconds, then calculate the orbital
speed in meters/sec. Once you do that determine the mass contained within the orbit in solar
masses.) E) 1011 solar masses.
39) A supernova occurred 10,000 years from now in a galaxy 50,000 light years away will be
observed on Earth C) 40,000 years from now.
40) Suppose that Hubble's constant were 20 kilometers per second per million light-years. How
fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion
is due only to Hubble's law.) B) away from us at 2,000 km/s
Lecture 17
Main-sequence stars are fusing hydrogen into helium in their cores like the Sun.
• Luminous main-sequence stars are hot (blue).
• Less luminous ones are cooler (yellow or red)
What is a Hertzsprung-Russell diagram?
– An H-R diagram plots stellar luminosity of stars versus surface temperature (or color or
spectral type).
• What is Spectroscopic Parallax?
• What is the significance of the main sequence?
– Normal stars that fuse H to He in their cores fall on the main sequence of an H-R diagram.
– A star's mass determines its position along the main sequence (high-mass: luminous and
blue; low-mass: faint and red)
What is the smallest mass a newborn star can have?
– Degeneracy pressure stops the contraction of objects <0.08MSun before fusion starts.
• What is the greatest mass a newborn star can have?
– Stars greater than about 150MSun would be so luminous that radiation pressure would blow
them apart.
– New observations may require raising this limit.
• What are the typical masses of newborn stars?
– Star formation makes many more low-mass stars than high-mass stars.
Lecture 18
How does a star's mass affect nuclear fusion?
– A star's mass determines its core pressure and temperature and therefore determines its
fusion rate.
– Higher mass stars have hotter cores, faster fusion rates, greater luminosities, and shorter
lifetimes
What are the life stages of a low-mass star?
– Hydrogen fusion in core (main sequence)
– Hydrogen fusion in shell around contracting core (red giant)
– Helium fusion in core (horizontal branch)
– Double shell burning (red giant)
• How does a low-mass star die?
– Ejection of hydrogen and helium in a planetary nebula leaves behind an inert white dwarf.
What are the life stages of a high-mass star?
– They are similar to the life stages of a low-mass star.
• How do high-mass stars make the elements necessary for life?
– Higher masses produce higher core temperatures that enable fusion of heavier elements.
• How does a high-mass star die?
– Its iron core collapses, leading to a supernova.
Lecture 19
What is a white dwarf? A white dwarf is the inert core of a dead star.
– Electron degeneracy pressure balances the inward pull of gravity.
• What can happen to a white dwarf in a close binary system?
– Matter from its close binary companion can fall onto the white dwarf through an accretion disk.
– Accretion of matter can lead to novae and white dwarf supernovae.
What is a neutron star? It is a ball of neutrons left over from a massive star supernova and
supported by neutron degeneracy pressure.
• How were neutron stars discovered?
– Beams of radiation from a rotating neutron star sweep through space like lighthouse beams,
making them appear to pulse.
– Observations of these pulses were the first evidence for neutron stars.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Lecture 20
What are the two types of star clusters?
– Open clusters are loosely packed and contain up to a few thousand stars.
– Globular clusters are densely packed and contain hundreds of thousands of stars.
• How do we measure the age of a star cluster?
– A star cluster's age roughly equals the life expectancy of its most massive stars still on the
main sequence
How do we measure the distances to galaxies?
– The distance measurement chain begins with parallax measurements that build on radar
ranging in our solar system.
– Using parallax and the relationship between luminosity, distance, and brightness, we can
calibrate a series of standard candles.
– We can measure distances greater than 10 billion light years using white dwarf supernovae as
standard candles
Lecture 23
How are the lives of galaxies connected with the history of the universe?
– Galaxies generally formed when the universe was young and have aged along with the
universe.
• What are the three major types of galaxies?
– The major types are spiral galaxies, elliptical galaxies, and irregular galaxies.
– Spirals have both disk and spheroidal components; ellipticals have no disk.
What have we learned?
• How are galaxies grouped together?
– Spiral galaxies tend to collect into groups of up to a few dozen galaxies.
– Elliptical galaxies are more common in large clusters containing hundreds to thousands of
galaxies.
How did Hubble prove that galaxies lie far beyond the Milky Way?
– He measured the distance to the Andromeda Galaxy using Cepheid variable stars as standard
candles.
• What is Hubble's law?
– The faster a galaxy is moving away from us, the greater its distance:
Velocity = H 0 × distance
How do distance measurements tell us the age of the universe?
– Measuring a galaxy's distance and speed allows us to figure out how long the galaxy took to
reach its current distance.
– Measuring Hubble's constant tells us that amount of time: about 14 billion years.
• How does the universe's expansion affect our distance measurements?
– Lookback time is easier to define than distance for objects whose distances grow while their
light travels to Earth.
• Why does the observable universe have a horizon?
– We cannot see back to a time before the beginning of the universe!