104 Stars

Front 1

An object that is formed by the gravitational collapse of an interstellar cloud, and is slowly contracting and heating up to become a star, is called

Back 1

a protostar

Front 2

As an interstellar cloud forms a new star and planetary system it ______

Back 2

contracts, heats up, and spins faster

Front 3

How can new stars form?

Back 3

Red Giant stars can pass through a giant molecular cloud and assemble new stars along the way.

Front 4

Protostars are

Back 4

slowly contracting and heating up.

Front 5

The lowest mass that a protostar can have and still become a star (i.e., start thermonuclear reactions in its core) is

Back 5

slightly less than 1/10 of a solar mass.

Front 6

Suppose that an astronomy news item announces the discovery of a brown dwarf. What is it that has been discovered?

Back 6

a object too massive to be a planet but not massive enough to be a star

Front 7

An object that is too massive to be a planet but not massive enough to be a star is called a

Back 7

brown dwarf.

Front 8

At approximately what temperature will fusion begin in the core of a pre–main-sequence star?

Back 8

5 million K

Front 9

What occurrence defines the end of the protostar phase of a star's life and the start of the main-sequence phase?

Back 9

Fusion begins in its core.

Front 10

What is happening in a star that is on the main sequence on the Hertzsprung-Russell diagram?

Back 10

The star is generating internal energy by hydrogen fusion, creating helium.

Front 11

T Tauri stars are at what stage of stellar evolution?

Back 11

early phase, during fusion while the star attempts to find radiative equilibrium

Front 12

Which of the following statements is characteristic of a T Tauri star?

Back 12

ejection of mass into space

Front 13

Which of the following are NOT very young stars or prestellar objects?

Back 13

red giants

Front 14

Which range of electromagnetic radiation is useful for observing new-born protostars within their gas and dust nebulae?

Back 14

infrared

Front 15

A main-sequence star has begun _______ after finding equilibrium

Back 15

to fuse hydrogen into helium

Front 16

The limit on the lifetime of a star is determined primarily by its _______.

Back 16

total mass and therefore its amount of available nuclear fuel

Front 17

What is the most important quantity on which the lifetime of a star depends?

Back 17

mass of the star

Front 18

How is the length of a star's lifetime related to the mass of the star?

Back 18

Higher-mass stars run through their lives faster and have shorter lifetimes.

Front 19

Why are the majority of stars in the sky in the main-sequence phase of their lives?

Back 19

This is the longest-lasting phase in each star's life.

Front 20

What is the next stage in a star's life after the main-sequence phase?

Back 20

red giant

Front 21

Stellar Nucleosynthesis

Back 21

is the process by which hydrogen and helium are converted into heavier elements.

Front 22

What are the products of helium burning in a star?

Back 22

carbon and oxygen

Front 23

What process is capable of generating the Sun’s luminosity for at least as long as it and the planets have been known to exist (approximately 4.6 billion years)?

Back 23

Nuclear fusion of hydrogen into helium.

Front 24

What is nuclear fusion?

Back 24

two nuclei sticking together to form a new, heavier nucleus

Front 25

At the present time, the energy of the Sun is generated

Back 25

in its central core only, by fusion of hydrogen nuclei.

Front 26

In another 4-5 billion years, when our Sun has fused about 10% of its available hydrogen supply into helium, it will ______ .

Back 26

swell up and become a red giant

Front 27

‘Heavy’ elements are made by nuclear fusion that occurs in the cores of _____.

Back 27

All of the above

Front 28

Which of the following objects does NOT represent the endpoint of a star's evolutionary life?

Back 28

red giant

Front 29

The majority of the elements heavier than hydrogen and helium in the universe are believed to have originated in

Back 29

the central cores of stars.

Front 30

What is the last nuclear burning stage in the life of a low-mass star like the Sun?

Back 30

fusion of helium nuclei to form carbon and oxygen

Front 31

A planetary nebula is

Back 31

an expanding gas shell surrounding a hot, white dwarf star.

Front 32

A white dwarf is

Back 32

a low-mass star at the end of its life.

Front 33

At which phase of its evolutionary life is a white dwarf star?

Back 33

very late for a small mass star, the dying phase

Front 34

In which order will a single star of about 1 solar mass progress through its various stages of evolution?

Back 34

T Tauri, main sequence, planetary nebula, white dwarf

Front 35

A white dwarf is about the same size as

Back 35

the Earth.

Front 36

A white dwarf is generating energy from what source?

Back 36

It no longer generates energy but is cooling slowly.

Front 37

A white dwarf star is supported from collapse under gravity by

Back 37

degenerate-electron pressure in the compact interior.

Front 38

Which of the following types of stars or stellar remnants cannot have a mass larger than about 1.4 times the mass of the Sun?

Back 38

white dwarf

Front 39

What prevents a neutron star from collapsing and becoming a black hole?

Back 39

Gravity in the neutron star is balanced by an outward force due to neutron degeneracy.

Front 40

What is believed to be the maximum mass for a neutron star?

Back 40

3 solar masses

Front 41

The diameter of a typical neutron star of 1 solar mass is predicted to be approximately

Back 41

that of an average city, about 20 km.

Front 42

What is the likely final fate of the core of a star that has a mass of 15 solar masses after completing its nuclear fusion burning phases?

Back 42

It collapses and becomes a black hole.

Front 43

The pulsed nature of the radiation at all wavelengths that is seen to come from a pulsar is produced by

Back 43

the rapid rotation of a neutron star that is producing two oppositely directed beams of radiation.

Front 44

Which of the following astronomical objects are most closely associated with pulsars?

Back 44

neutron stars

Front 45

Which of the following will a high-mass star (say, 25 times the mass of the Sun) NOT do at or near the end of its life?

Back 45

eject its outer layers and become a white dwarf

Front 46

Which force induces the core to condense and collapse in massive stars at the conclusion of each episode of nuclear fusion, such as the carbon, oxygen, and silicon fusion cycles?

Back 46

gravity

Front 47

A high-mass star near the end of its life undergoes successive cycles of energy generation within its core in which gravitational collapse increases the temperature to the point where a new nuclear fusion cycle generates sufficient energy to stop the collapse. This process does not work beyond the silicon fusion cycle which produces iron. Why is this?

Back 47

Fusion of iron nuclei into heavier nuclei requires energy rather than producing excess energy and therefore will not produce the additional gas and radiation pressure to halt the collapse.

Front 48

What is the source of most of the heavy elements on the Earth and in our own bodies?

Back 48

explosive nucleosynthesis during supernova explosions of massive stars

Front 49

How did supernova SN 1987A differ from most other observed supernovae?

Back 49

The star was a blue supergiant when it blew up, rather than the expected red supergiant.

Front 50

Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Why is this? (HINT: Think about the type of star that gives rise to each of the two types of supernova.)

Back 50

Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen.

Front 51

Ancient Chinese astronomers recorded the appearance of what phenomenon in 1054 AD?

Back 51

a supernova, visible in daylight

Front 52

A black hole can be thought of as

Back 52

strongly curved space.

Front 53

If a black hole is truly black and has an escape velocity greater than the speed of light such that no light can escape it, where do the X rays come from in the black hole candidates so far identified?

Back 53

from the matter surrounding the black hole, which is highly condensed and hence very hot because of the intense gravitational field.

Front 54

At first it was always thought that nothing could escape from a black hole, yet astronomers are locating black hole candidates by the X rays they emit. Why do they see X rays coming from a black hole?

Back 54

The X rays come from highly compressed matter in the accretion disk outside the event horizon of the black hole.

Front 55

The intense X rays emitted by a suspected black hole are generated by what physical mechanism?

Back 55

frictional and compressional heating as material moves into the hole

Front 56

Where would you look for a supermassive black hole?

Back 56

in the center of a galaxy

Front 57

The only parts of a non-rotating black hole that are necessary for its complete description are

Back 57

its center, or singularity, and its "surface" or event horizon.

Front 58

The words "Schwarzschild radius" refer to

Back 58

the distance from the center of a black hole at which the escape velocity becomes equal to the speed of light.

Front 59

As relates to the mass of the black hole, the Schwarzchild radius

Back 59

is larger, the more massive the black hole.

Front 60

What is the law of cosmic censorship?

Back 60

There can be no naked singularities; every black hole must be surrounded by an event horizon.

Front 61

Which of the following statements correctly describes "cosmic censorship"?

Back 61

The only way into or out of a singularity is through an event horizon.

Front 62

Suppose you discover a naked singularity without its surrounding event horizon. What effect would such an object have on the neighboring region of space?

Back 62

The effects of a naked singularity are completely unpredictable.

Front 63

Which properties of the matter inside a black hole can be measured from outside the black hole?

Back 63

mass, electric charge, and angular momentum

Front 64

Take two identical, nonrotating, 5-solar-mass black holes and place them side by side. Add one solar mass of pineapples to the left-hand one and one solar mass of radioactive uranium to the right-hand one (without changing their electric charge or their rotation). Afterward, how do these two black holes differ?

Back 64

They do not differ at all.

Front 65

Take two identical, nonrotating, 5-solar-mass black holes and place them side by side. Add one solar mass of neutrons to the left-hand one and one solar mass of protons to the right-hand one (without changing the rotation of the black holes). Afterward, how do these two black holes differ?

Back 65

The left-hand one is electrically neutral and the right-hand one will have an enormous electric charge.

Front 66

If you were to enter the event horizon of a black hole,

Back 66

there would be nothing you could do to prevent yourself from falling directly into the singularity at the center.

Front 67

What appears to happen to a clock as it approaches and reaches the event horizon around a black hole, when viewed by a remote observer?

Back 67

It appears to slow down and stop.

Front 68

A space freighter accidentally drops a steel beam while passing a black hole, and the beam starts falling toward the black hole with the long axis of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon?

Back 68

It is stretched in length.

Front 69

If you were watching a friend (or better still, an enemy!) who has fallen as far as the event horizon of a black hole, what would you measure as his heartbeat (apart from effects caused by his adrenaline level)?

Back 69

It would appear to be zero, his heart would appear to have stopped.

Front 70

The evolution of a star is controlled mostly by its

Back 70

initial mass.

Front 71

The event horizon of a non-rotating black hole is located at the

Back 71

distance of a Schwarzschild radius from its center

Front 72

How much longer can the Sun continue to generate energy by nuclear reactions in its core?

Back 72

about 5 billion years