Final Exam
How many stars similar to our sun would need to be collected at one place to equal the power output of Sgr A*?
a million 1,000,000
The total luminosity, at all wavelengths, of the source Sgr A* is approximately
a million times the luminosity of our sun.
Which of the following objects is closest in size to a black hole formed from the collapse of a star?
a neutron star
A steady X-ray signal with sudden bursts lasting a few seconds each is probably caused by
a neutron star in a binary system.
The idea that a supernova is preceded by a huge burst of neutrinos is
a prediction that has now been observed.
Type I supernovas have the following properties:
a spectrum with no hydrogen lines and a standard maximum brightness.
The overall shape of our Milky Way Galaxy is though to be
a spiral somewhat like the nearby Andromeda Galaxy.
A planetary nebula forms when
a star becomes a white dwarf.
A neutron star in orbit near a normal star is expected to emit
both a constant X-ray signal and X-ray bursts.
The source that is called Sgr A* emits
both infrared light and radio waves.
The property of electron-degenerate matter that is important in the evolution of a star is that this type of matter
caanot be compressed and heated
In our Milky Way Galaxy, the Orion arm is the
closest one to the sun
The intense magnetic field of the Crab pulsar causes its rate of spin to
decrease
When a red giant star begins to burn helium, its diameter
decreases but not to its main sequence size.
The surface temperature of a white dwarf star
decreases from millions of degrees K to zero.
A red subgiant star is one that has a
decreasing surface temperature and nearly constant brightness.
Submissions are not permanently recorded The red subgiant stage of a star is best described by
dropping tempweature and constant brightness
Elements with more protons and neutrons than iron (Uranium for example), are believed to have formed
during supernova explosions of very massive stars.
Nuclei such as protons do not fuse at low temperatures because their speeds are not enough to overcome their
electrical repulsion
Which of the following particles would be electrically attracted by a positron?
electron
Which of the following particles would be electrically attracted by a proton?
electron
The core of a red supergiant star stops shrinking because its
electrons touch each other
A brown dwarf shines primarily with
energy left over from its formation.
The temperature of a gas measures the
energy of motion of its atoms or molecules
The point at which even an outwardly directed light ray is pulled into a black hole is called the
event horizon
Supernova explosions tend to
form elements heavier than iron.
Stars that are much less massive than our Sun
form more slowly and burn slower.
In an evolved high-mass star, when the electrons combine with protons to form a pure neutron core, the reaction
generates a neutrino burst
The origin of the energy that is released in a supernova explosion is
gravitational energy from the core collapse.
A star leaves the main sequence when
it runs out of hydrogen at its core
The reason that the Crab Pulsar is slowing down is
its magnetic field is dragging through nearby gas.
When a star first moves off the main sequence,
its surface temperature drops and its brightness first stays about the same and then increases.
The iron core of an evolved massive star collapses because
its temperature rise stops when iron nuclei come apart.
In comparison to Cepheid variables, RR Lyra variable stars are
less luminous and more common.
On a HR diagram, a visible white dwarf star is in the
lower left corner
The motions of the stars near Sgr *A make it possible to determine its
mass
The X-rays that reveal the possible presence of a black hole are the result of
matter heating up as it falls toward the hole.
Near the center of the Milky Way there is an intense radio source whose mass is approximately three
million solar masses within several light days of the center.
In comparison to RR Lyra variables, Cepheid variable stars are
more luminous and less common.
The arms of a spiral galaxy such as ours stand out because they contain
most of the brightest stars
When the temperature of gas increases, its molecules
move faster
In a spiral galaxy, long-lived stars such as our Sun
move in and out of spiral arms
When the temperature of a gas decreases, its molecules
move slower
When the helium fuel runs out at the center of a low-mass star like our Sun, it
moves off the horizontal branch
When a white dwarf star collects matter from a neighboring star, fusion reactions on the surface of the white dwarf cause
novas
One conclusion that was drawn from the gradual slowing of the radio signals from the Crab Nebula was that they were probably
of natural origin
On a Hertzsprung-Russel diagram, stars that are burning Helium at their cores are found
on the horizontal branch
In a star with 15 to 20 times the mass of our Sun nuclear burning at the center stops
only when an iron core develops.
The Population II stars of our Milky Way
orbit the central bulge in all directions.
The Population I stars of our Milky Way
orbit the central bulge only within the disk.
Our Sun's location in the Milky Way is closest to the
orion arm
Objects such as the Great Nebula in Andromeda were once called extragalactic nebulae. It is now realized that they are actually
other galaxies much like our own
The event horizon of a black hole is the point at which
outwardly directed light rays are pulled into the hole.
From the motions of nearby stars, the mass of the radio source Sgr A* is found to be spread
over a region less than a few light days across.
The formation of a new white dwarf is usually accompanied by
planetary nebula
Which of the following particles would be repelled by a proton?
positron
The formation of electron-degenerate matter in the carbon core of a solar-mass red super giant
prevents carbon-burning from starting.
A hydrogen atom with its electron removed (a H+ ion in other words) is actually a
proton
An atom of ordinary hydrogen consists of an electron and a
proton
Which of the following particles would be attracted to a neutron through the strong force?
proton
Neutron stars are often observed as
pulsars
A star that is cooling and swelling just enough to keep the same total brightness could be a
red subgiant
Our Sun is a type G2V star on the main sequence. As it ages and uses up its fuel we expect it to
remain a G2V star until it leaves the main sequence.
Nuclear fusion requires high temperatures because nuclei
repel each other
When a red giant star beings to burn helium, it
returns part way to the main sequence in an HR diagram.
A black hole that has formed from the collapse of a star is expected to be
similar in size to a neutron star.
The 'Little Green Men Standard Time' hypothesis for the repeating radio signals seen in 1968 was rejected partly because the repetition rate was
slowing down
A star that is in the lower left corner of an HR diagram is most likely a
white dwarf star
The diameter of the Milky Way Galaxy is close to
100,000 light years
A star that is approximately the size of the Earth is probably a
white dwarf star
The mass of a carbon atom is 12.00 amu while the mass of a helium-4 atom is 4.003 amu. If three atoms of helium fuse to form carbon, how much mass is converted into energy?
.0009 amu
The mass of a carbon atom is 12.00 amu while the mass of a helium-4 atom is 4.003 amu. If a gamma ray photon splits a carbon atom into three Helium atoms, how much energy is converted into mass?
.009 amu
The closest star to our sun is about four light years away. In the center of our galaxy, a typical distance between neighboring stars would be
.04 light years
The mass of a carbon atom is 12.00 amu while the mass of a deuterium atom is 2.014 amu. If a gamma ray photon splits a carbon atom into six deuterium atoms, how much energy is converted into mass?
0.084 amu
The diameter of a white dwarf star might be
10,000 miles
Our Sun is expected to last for about 10 billion years. Which of these is a likely lifespan for a star with 20 times the mass of our Sun?
10-15 million years
The distance from our sun to the center of the Milky Way Galaxy is roughly
30,000 light years
Type II supernovas have the following properties:
: a spectrum with hydrogen lines and a variable maximum brightness.
The red supergiant phase of a star is caused by
: the exhaustion of helium at its core.
Which of the following star-like objects would most likely be considered to be a brown dwarf?
Gliese 229 B, luminosity and temperature both below type M9V.
Within our own Milky Way Galaxy, our sun is a typical member of
Population I
The thickest part of the visible Milky Way is near the constellation
Sagittarius.
High protostellar winds of ejected gas occur when the protostar is in the
Tau Tari phase
The object Gliese 229B glows in the infrared but is much cooler and dimmer than a class M star and shows traces of lithium that a normal star would quickly burn up in the nuclear reaction that occurs in its core. This object is most likely
a brown dwarf
When an interstellar cloud fragment does not have enough mass to form a star powered by nuclear fusion, but gets hot enough to glow for a while, it is called a
a brown dwarf
For a star to give rise to a Nova, the star must be
a member of a multiple star system.
Which of the following stars or star systems could possibly give rise to a nova:
a white dwarf in orbit around a red giant.
A nova occurs when
a white dwarf steals fuel from a neighbor.
A type I supernova occurs when
a white-dwarf collapses
A star that evolves off the main sequence in about 10 million years probably has
about 20 times the mass of our sun
When the iron nuclei in the core of an evolved high-mass star start to come apart, they
absorb energy and limit the core temperature.
The onset of Helium burning at the core of a star normally begins with
an explosion in the helium core
The first red giant stage of a one solar mass star's life usually ends with
an explosion in the helium core.
Because of the electrical repulsion between atomic nuclei, nuclear fusion happens only
at high temperatures
When nuclear fusion reactions stop in a star similar to our own Sun, the star
becomes a white dwarf
When we use a Hertzsprung-Russell plot to describe the evolution of a collapsing gas cloud to a protostar and then to a regular star, we find that the object's position on the plot
begins far from the main sequence and moved onto it, where it stops.
A star that forms an iron core most likely has a mass of
between 15 and 20 solar masses.
High protostellar winds of ejected gas occur
between the initial contraction and the ignition of nuclear burning.
When nuclear fusion reactions stop in a star similar to our own Sun, the star's outer layers
blow off as a planetary nebula.
The light from a new-born white dwarf star will most likely be
blue
Near the end of the life of a massive star, an intense burst of neutrinos
happens when the electrons are eliminated
Black holes
have been detected because infalling matter emits X-rays.
Cepheid variable stars with the same period
have similar luminosities.
Cepheid variable stars with the same luminosity usually
have similar periods
Stars on the horizontal branch of the HR diagram are burning
helium at their centers
The explosive ignition of a star's helium core is called a
helium flash
A proton is the nucleus of an atom of
hydrogen
The stars of the Milky Way are found
in a band of stars stretching across the sky.
Stars with more than 15 times the mass of our Sun usually evolve off the main sequence along a path in the HR diagram that
is mostly horizontal
The stars of the Milky Way are all near a great circle on the Celestial Sphere. This great circle
is none of the other listings here
The constellation Sagittarius is where the Milky Way
is thickest
A star leaves the horizontal branch in the HR diagram when
it runs out of helium at its core
At the center of our Milky Way galaxy, neighboring stars are typically
much closer together than neighbors of our sun.
The gravitational energy that is released when the core of a massive star collapses is usually
much larger than the nuclear energy that the star has generated.
The mass of Barnard's Star is about 1/6 the mass of our own Sun. Our Sun is expected to have a total life span of about 10 billion years. The life span of Barnard's Star is expected to be
much longer (because less massive stars do everything much more slowly)
The mass of Betelgeuse is about 20 times the mass of our own Sun. Our Sun is expected to have a total life span of about 10 billion years. The life span of Betelgeuse is expected to be
much shorter (the more massive - the faster the demise)
Relative to the Milky Way family of stars, our sun is
neither at the center nor at the edge.
Which of the following particles has the smallest mass?
neutrino
The first signal received from the 1987 supernova SN1987A came in the form of
neutrinos
Which of the following particles has almost the same mass as a proton?
neutrn
Which of the following particles has the largest mass?
neutron
Which of the following particles would be attracted to a proton through the strong force?
neutron
Extragalactic nebulae such as the Great Nebula in Andromeda were not immediately recognized as galaxies similar to our own Milky Way because they were thought to be
smaller, nearby objects
A pulsar is really a
spinning neutron star
Once a star has evolved onto the Main Sequence in the HR diagram, it
stays at the same point until it runs out of fuel.
When the hydrogen fuel runs out at the center of a main sequence star, the star
swells up and becomes a red giant.
When the helium fuel runs out at the center of a horizontal branch star, it
swells up and becomes a red supergiant.
The average energy of motion of an atom or molecule in a gas is called its
temperature
During the Tau Tauri phase of a protostar's evolution,
the brightness decreases
The size of a typical white dwarf star is comparable to the size of
the earth
Electron degenerate matter is matter in which
the electrons are touching each other so that they cannot be compressed.
The first red giant phase of a star is caused by
the exhaustion of hydrogen at its core.
The 'helium flash' refers to
the explosive ignition of a star's helium core.
The mass of Sgr A* has been determined by observing
the motions of stars near it.
The final core collapse that leads to a supernova is ended when
the neutrons touch each other.
The position of a protostar on an HR diagram changes because
the size and temperature of the protostar change.
A Helium-3 nucleus consists of two protons and one neutron. The main force that holds it together is
the strong force
A normal Helium nucleus consists of two protons and two neutrons. The protons actually repel each other because they have the same charge. The main force that holds this nucleus together is
the strong force
The period of a proto-star's evolution when its size and brightness decrease just before the ignition of nuclear reactions in its core is called
the tau-tauri phase
Our sun is roughly at the center of
the visible part of the milky way
When the core of a star collapses while inside the star, the result is a
type II supernova
A star that is 10,000 miles in diameter is probably a
white dwarf star
Stars with more than 15 times the mass of our Sun usually evolve from the main sequence to red giants
without pausing while getting cooler at almost constant brightness.
