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.