Honors Astronomy Final 2
The ESA satellite which gave us our most accurate distances to stars is called
Hippacros
If two stars differ in brightness by 5 magnitudes, the light ratio received by us is ______ to 1
100x
In comparing first magnitude Deneb with second magnitude Polaris, we find that
Deneb appears 2.5x brighter to us than Polaris
What are the two most important intrinsic properties used to classify stars?
Luminosity and Surface Temperature
If a star has a parallax of 0.05″, then its distance in light years is about
66 Light Years
If a star is found by spectroscopic observations to be about 500 parsecs distant, its parallax is
.002″
Hipparcos observations have given us good data on stars out to about
200 parsecs
About how many stars has Hipparcos given us accurate distance data on?
A million, those with parallaxes of .005″ or large
Which of the following spectral types is the hottest?
K4
G2
G5
H3
K4
G2
G5
H3
G2
While Sirius, the Dog Star, is type AO, a star just a step hotter than M0 is a related:
M1
K9
B9
A1
M1
K9
B9
A1
K9
The Hertzsprung-Russell Diagram plots ______ against the spectral type or temperature.
Luminosity or Absolute Magnitude
Two stars which differ by 5 magnitudes in apparent brightness have the same parallax; thus, one star must be intrinsically ______ times as luminous as the other.
A hundred
Stellar masses are determined directly by observation of the orbits and periods of ______ stars.
All types of binary
In what range of masses are most stars found
.1 to 20 solar masses
Why are star clusters almost ideal “laboratories” for stellar studies?
Stars in clusters have the same age, similar composition, and are at the same distance away
Perhaps the greatest of the Greek astronomers, _______ compiled the first catalog of stars, accurately measured their positions, and defined the basic system of stellar brightnesses.
Hipparcos
Which of the following spectral types is the hottest?
A5
O9
G2
K9
A5
O9
G2
K9
O9
Which of these pairs of spectral types is most similar in temperature?
M2 and M5
B1 and A1
K9 and M0
F1 and G9
M2 and M5
B1 and A1
K9 and M0
F1 and G9
K9 and M0
What physical property of a star does the spectral type measure?
Temperature
The star’s color index is a quick way of determining its
Temperature
Which of the following is the most common type of star?
Main Sequence
Which of the following apparent magnitudes is the brightest?
+3.2
+5.0
-1.1
+15.8
+3.2
+5.0
-1.1
+15.8
-1.1
What is the absolute magnitude of our Sun?
-23
+4.8
+9.32
-1.4
-23
+4.8
+9.32
-1.4
+4.8
What is the single most important characteristic in determining the course of a star’s evolution?
Mass
The absolute magnitude of a star is its brightness as seen from a distance of
10 parsecs
Which statement about stellar motion is incorrect?
the transverse velocity is measured by the proper motion
the transverse velocity is measured by the proper motion
the Pythagorean theorem relates space, transverse, and radial velocities.
proper motion is measured over intervals of exactly six months
the radial velocity is measured by the Doppler shift
proper motion is measured over intervals of exactly six months
If the radial velocity were -3 km/sec, and the transverse velocity were +4 km/sec, then
The space velocity would be 5 km/sec.
What characteristic of the stars in a binary system can be determined by knowing the period of the stars’ common orbit and the distance between them?
Mass
Which type of binary can have their sizes measured directly by photometry?
Eclipsing
The HR diagram can be a plot of _________.
absolute magnitude versus color index
What is the typical main sequence lifetime of a B-type star?
20 million years
What is the typical main sequence lifetime of a G-type star?
10 billion years
What is the typical main sequence lifetime of a M-type star?
A trillion years
A nearby star has a parallax of 0.2 arc seconds. What is its distance?
5 pc
Procyon lies about 13 light years distant, thus its parallax is about:
.25″
In the H-R diagram, the bright blue-white stars that dominate the naked eye sky lie to the
Upper left quadrant
On the H-R diagram, the Sun lies:
About the middle of the main sequence
On the H-R diagram, white dwarfs lie Sirius B and Procyon B lie:
To the lower left
On the H-R diagram, red supergiants like Betelguese lie:
To the top right
______ have masses like that of the Sun, and radii like that of the Earth.
White dwarfs
What is proper motion?
It is the annual apparent motion of a star across the sky
In order to turn a star’s proper motion into its space velocity, we must also know:
Its distance and radial velocity
Which of the following best describes the size and distance relationship of our Sun and the nearest star?
Two golfballs separated by 100 kilometers
Compared to the size of the Sun, in what range of sizes are most stars found?
0.01 to 100 solar radii
How might the most common occurring stars be described, based on our stellar neighborhood?
M-type main sequence stars
What are the characteristics of an open cluster of stars?
a few hundred, mostly main sequence, stars
What are the characteristics of globular cluster stars?
old age and hundreds of thousands of stars
What makes the subject of star formation so difficult and complex?
Stars live too long to be observed from birth to death.
A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?
From the release of gravitational energy as the protostar continues to shrink
Which of these is not typical of a condensing protostar?
Fusion of helium into carbon in their cores
What is the critical temperature at which hydrogen can fuse into helium in the star’s core?
10 million K
What happens when an interstellar cloud fragment shrinks?
Density rises.
Temperature rises.
Pressure increases
Temperature rises.
Pressure increases
What is characteristic of a main sequence star
The rate of nuclear energy generated in the core equals the rate radiated from the surface.
Most stars probably formed
In clusters
How long does it take for a star like our Sun to form
50 million years
Which relationship concerning the mass of protostars is false
The more massive ones will be the hottest and most luminous.
The more massive ones will reach the main sequence first.
The more massive ones glow red, accounting for the color of H II regions.
The more massive ones create the ultraviolet to cause H II regions to glow
The more massive ones glow red, accounting for the color of H II regions
What is the key factor that determines the temperature, density, radius, luminosity, and pace of evolution of a protostellar object
Mass
When an H II region is observed, it signals what stage in stellar formation
Depending on their masses, the stars inside may be at different stages of formation
What is the size of a typical interstellar cloud that is dense enough to form stars
10 pc
For gravity to contract a spinning interstellar cloud, there needs to be sufficient
Mass
As a star forms, the photosphere first appears
When the protostar forms
If the initial interstellar cloud in star formation has a mass sufficient to form hundreds of stars, how does a single star form from it
The cloud fragments into smaller clouds and forms many stars at one time.
A cloud fragment too small to form a star becomes
A brown dwarf
Which event marks the birth of a star
Fusion of hydrogen atoms into helium atoms
At what stage of evolution do T Tauri stars occur
When a protostar is on the verge of becoming a main sequence star
How many hydrogen atoms does it take to make a typical star
10^57
How are T Tauri stars characterized observationally
By sudden changes in their brightness
Evidence for star formation theory comes from
Studying different objects at different stages and piecing together an evolutionary picture.
How long does it take an M-type star to form, compared to the time for a solar-type star to form
20 times as long
When a typical open cluster forms, which type of stars are formed most often
low mass M type dwarfs
A star will evolve “off the main sequence” when it uses up which of the following?
most of the hydrogen in the core
On the main sequence, massive stars do which of the following
burn their hydrogen fuel more rapidly than the Sun
When the Sun is on the red-giant branch, it will be found where on the H-R diagram
Upper right
After the core of a Sun-like star starts to fuse helium on the horizontal branch, the core becomes which of the following
hotter
When the Sun leaves the main sequence, it will become which of the following
brighter
A star like the Sun will end up as what
a white dwarf
The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally ______.
black hole
none of these
neutron star
nova
black hole
none of these
neutron star
nova
none of these
The helium flash converts helium to the heavier element _____
Carbon
How many helium atoms must be fused at 100 million K in the helium flash
Three
Which of the following best describes the evolutionary track followed in the HR diagram for the most massive stars
Horizontally right
What is used, observationally, to determine the age of a star cluster?
the luminosity at the main-sequence turnoff
What is the source of pressure in the core of a red giant that resists the force of gravity
electrons which have become incompressible
In a white dwarf, we have packed the mass of the Sun into the volume of Earth, so the density is
a million times that of the Sun
What, in addition to its HR diagram, is needed to age-date a star cluster
theoretical models of stellar evolution
What characteristic of a star cluster is used to determine its age
the main sequence turnoff
The brightest stars of a young open cluster will be
massive blue main sequence stars
In globular clusters, the brightest stars will be:
Red supergiants
A high-mass star dies more violently than a low-mass star because
It generates more heat and its core eventually collapses.
A ______ is a relatively gentle mass-loss event which allows a star to peacefully readjust its structure into a white dwarf configuration
planetary nebula
Which of these will the Sun probably become in the very distant future
planetary nebulae
The evolution of stars appears inevitable. But what likely circumstance can radically alter this evolutionary sequence
The stars can be in a short period binary system.
Which statement is true, in terms of stellar evolution
sooner or later, gravity wins
Can a star become a red giant more than once
yes
Which statement about blue stragglers is false
They are much more massive than any other stars known
If one star of a binary fills its Roche lobe and is spilling matter onto the other, then the system is a:
mass-transfer binary
If two stellar cores share a single envelope, we have a:
Contact binary
What results from the mass loss from K and M red giants
The wind is rich in dust particles and molecules, including diamonds
In a star cluster, just as the most massive stars are evolving into giants and supergiants, what is happening for the lowest mass stars
They are just starting to approach the zero-age main sequence
Luminous hot stars and luminous cool stars
have stellar winds, but each are driven by a different source
What is a typical age for a globular cluster
12 billion years
What temperature is needed to fuse helium
100 million K
What are black dwarfs?
Cooled off white dwarfs
Which of the following is true regarding planetary nebulae
They are the ejected envelopes of highly evolved low-mass stars
The Roche lobe of a star in a binary star system
is, in terms of the star’s gravity, its “zone of influence.”
What is a planetary nebula
The ejected envelope of a red giant surrounding a stellar core remnant.
Astronomers talk about “low-mass” and “high-mass” stars with regard to their evolution. In units of solar masses, what is the dividing line, that is, the lowest mass for a high-mass star
8 solar masses
What inevitably forces a star like the Sun to evolve away from being a main sequence star
It builds up a core of helium
In the evolution of massive stars, what is the significance of the temperature 600 million K?
It is the temperature needed for carbon burning
A star spends most of its life
as a main sequence star.
What is the significance of 100 million K to the core of a star
Temperature need to start triple alpha process and turn helium into carbon.
The “helium flash” occurs at what stage in stellar evolution
Red giant
Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible
The core contracts, raising the temperature of the region of hydrogen shell-burning
A white dwarf can dramatically increase in brightness only when which of the following applies
It has another star nearby
Which of the following stars will become hot enough to form elements heavier than oxygen
A Star that is eight times more massive than the Sun.
When does a massive star become a supernova
When it forms iron in its core
An observable supernova should occur in our Galaxy how often
About once every century
Which one of the following does not provide evidence that supernovae have occurred in our Galaxy
The existence of binary stars in our galaxy
Most of the carbon in our bodies originated where
the core of a red giant star
The silver atoms found in jewelry originated where
A supernova
A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object
Nova
For a nova to occur, the system must have already been a:
mass-transfer binary
Which type of heavy atomic nuclei are most common, and why
Even numbered elements, for helium is “giant food” for everything beyond itsel
Nearly all the elements found in our environment were formed inside stars, except for
Hydrogen and helium
The production of which element in the core of a highly evolved giant leads to type II supernovae
Iron
Why does neutron capture work
Neutrons have no repulsive barrier to overcome in combining with positively charged nuclei
What is the only way that a white dwarf can suddenly explode in a type I supernova
If it’s a member of a mass-transfer binary system
What is stellar nucleosynthesis
The formation of heavier elements inside stars
Of the elements in your body, the only one not formed in stellar nucleosynthesis is
Hydrogen
How long does it take a stellar iron core to collapse
One second
The heaviest nuclei of all are formed
By neutron capture during a supernova explosion
An iron core cannot support a star because
iron cannot fuse with other nuclei to produce energy.
What direct evidence do astronomers have that supports the heavy element formation in stars
Light curves of type-I supernovae
Gamma-ray emissions from decay of cobalt-56 in supernovae
Observed elemental abundances
What was most surprising about SN1987A
The parent star was a B supergiant, not a red supergiant.
The upper mass limit of 1.4 solar masses for white dwarfs won a Nobel prize for
Chandrasekhar
The Chandrasekhar mass limit is ______.
1.4 solar masses
A 20 solar mass star has a main sequence lifetime of 10 million years, yet its iron core exists for only about how long
Less than a day
A 20 solar mass star has a main sequence lifetime of 10 million years, yet its iron core exists for only about how long
less than a day
As a star evolves, heavier elements tend to form by various processes. Which of the following is not one of these processes
Neutronization
What is the reason a type-II supernova slows its dimming after about 2 months
Energy is released from the decay of radioactive cobalt-56 to iron-56
The transformation of cobalt 56 into iron 56 is an example of
the weak force and nuclear fission
The making of abundant iron nuclei is typical of
type II supernovae
What made supernova 1987a so useful to study
its progenitor had been observed previously
being in the Large Magellanic Cloud, its distance was immediately known
it occurred in modern times and within easy reach of large telescopes
Where was supernova 1987a located
In our companion galaxy, the Large Magellanic Cloud
Which of these is least likely to happen
recurrent supernovae of type I
Which of these is the likely progenitor of a type I supernova
a mass-transfer binary, with the white dwarf already at 1.3 solar masses
Which of these is the likely progenitor of a type II supernova
an evolved red giant which is just starting to make silicon in its core
Which of the following does not fit a type I supernova
Implosion-explosion of the core of a massive star
A star can be a supernova
once
The supernova that formed M-1, the Crab Nebula, was observed in what year
1054 AD by the Chinese
What is the amount of energy emitted in the form of neutrinos, during a supernova explosion, compared to the amount of energy radiated as electromagnetic radiation
100 times as much
What is the total energy radiated by a supernova equal to?
1 billion suns
The total energy emitted by the brightest nova explosions is about
1 million suns
What produces a type-I supernova
Mass transfer to a white dwarf in a binary where the Chandrasekhar mass is exceeded
When helium capture occurs with a carbon-12 nucleus, what results
oxygen-16
When two silicon-28 nuclei fuse, the initial result is
nickel-56
What evidence is there that supernovae really have occurred
Supernova remnants.
Crab Nebula.
The explosions themselves
Crab Nebula.
The explosions themselves
When a stellar iron core collapses, large numbers of neutrinos are formed, then
They immediately pass through the core and escape to space
A recurrent nova can eventually build up to a
type I supernova
In order of visual luminosity at the start, which is most luminous
a type I supernova
Which of these do not depend on a mass-transfer binary to occur
a type II supernova
The alpha process tends to produce chiefly
even numbered elements
Which of the following is not an argument for Cygnus X-1’s being a true black hole
The mass of the visible B star is even greater than Cygnus X-1, at around 30 solar masses
What explanation does general relativity provide for gravity
Gravity is a result of curved spacetime
What makes the Crab pulsar somewhat unusual among pulsars in general
It is rather bright at visible wavelengths.
Three terrestrial planetary-sized masses have been discovered orbiting what type of object
a millisecond pulsar
What compelling evidence links pulsars to neutron stars
Only a small rotating source of radiation is thought to be able to emit precisely timed pulses such as those from pulsars
The key to identifying a black hole candidate in a binary system is the following
the unseen companion in the system must have a sufficiently high mass
The observed slowing of a clock in the vicinity of a black hole is a prediction of
General Relativity
Which of these is least likely to exist
a 1.8 solar mass white dwar
Almost half of all known millisecond pulsars are found in what type of object
globular clusters
Who discovered the first object that eventually became known as a pulsar
Jocelyn Bell
Who received the Nobel Prize in Physics for relating pulsars to neutron star formation
Anthony Hewish
The supernova of 1054 AD produced
a pulsar with a period of 33 milliseconds, visible optically.
Which of the following is not a property of the first discovered pulsar (nor any other pulsar)
emissions only in the visible part of the spectrum
In the Lighthouse model
if the beams sweeps across us, we can observe the pulse
What are X-ray bursters
They are neutron stars on which accreted matter builds up, then explodes in a violent nuclear explosion
What is Cygnus X-1?
A leading candidate for being a black hole
X-ray bursters occur in binary star systems. What are the two types of stars that must be present to make up such an object
a main sequence or giant star and a neutron star
Which of the following are attracted by gravity
any object with mass
electromagnetic radiation
neutrinos
electromagnetic radiation
neutrinos
Which of the following can actually escape a black hole?
none of these
very high energy gamma-rays
very low energy radio waves
electrons
none of these
very high energy gamma-rays
very low energy radio waves
electrons
None of these
In a “hypernova”, the very energetic supernova creates a:
black hole
While perhaps affected by rotation and magnetism, we think the lower limit for black holes is
Schwartzchild’s limit of 3 solar masses
Which statement about gamma ray bursts is not correct
They seem to be coming from far beyond the Milky Way, in other host galaxies.
In seconds, they seem to radiate hundreds of times more energy than do supernovae.
They are a scaled up version of the X-ray bursts, with more massive stars involved.
Millisecond flickering implies they can be only a few hundred kilometers in size.
They are a scaled up version of the X-ray bursts, with more massive stars involved.
What would happen if mass is added to a 1.4 solar mass white dwarf
The star would erupt as a type I supernova
What would happen if mass is continually added to a 1.4 solar mass neutron star
The star would eventually become a black hole