Test 1 Flashcards
The blue colour of a nebula arises because…
The blue light is scattered most efficiently by dust in the nebula.
A dark nebula emits energy mostly in the form of…
Infrared radiation.
A nebula which produces light by fluorescence is called _____ nebula.
Emission
A bluish nebula is called _____ nebula.
Reflection
The spin rate of a pulsar…
Decreases over time.
About one quarter of material in a nebula is…
Helium.
The wavelength of a source of light approaching the event horizon of a black hole is…
Redshifted.
Which one of these stars spends more time in protostar stage? One solar mass star or ten solar mass stars.
One solar mass star.
True or false? The stronger the force of gravity on a clock, the faster it runs.
False.
During the protostar stage, a star derives its energy from…
Gravitational contraction.
A protostar with mass 0.3 solar mass will become…
A red dwarf.
Stars like the Sun do not form iron cores during their evolution because…
Their cores never get hot enough to form iron by nucleosynthesis.
Which of the following sequences describes the evolution of the Sun from young to old?
Protostar, main-sequence, red giant, yellow giant, red giant, white dwarf.
The non-fusing dead core of a star is supported against its collapse by…
Degenerate electrons.
The main-sequence of the Sun is estimated to be…
10 billion years long.
Once the hydrogen in the Sun’s core is fused into helium, further fusion of hydrogen into helium will go on in…
A shell surrounding the helium core.
When a medium-mass main-sequence star exhausts its core hydrogen fuel supply…
The core shrinks while the rest of the star expands.
The helium burning into carbon in the core of a medium mass star proceeds via…
Triple alpha-process.
Planetary nebula is…
A glowing shell of material ejected by a dying medium-mass star.
True or false? If the mass of an object composed of degenerate material increases, the radius decreases.
True.
True or false? White dwarfs with masses in excess of two solar masses have been observed.
False.
Which one of these white dwarfs has a larger radius? One solar mass white dwarf or half a solar mass white dwarf.
Half a solar mass white dwarf.
A white dwarf is composed of…
Carbon nuclei, some oxygen nuclei and degenerate electrons.
The gravitational collapse of a high-density white dwarf prevented by…
The pressure created by degenerate electrons.
The density of a while dwarf is about…
10 grams per centimeter cubed (ie, equal to typical metallic density).
True or false? There are hydrogen spectral lines in the spectrum of Type Ia supernova.
False.
Chandrasekhar’s limit is…
The maximum mass of a body composed of degenerate matter.
Type Ia supernova occurs…
In a white dwarf-star binary system when the mass transfer pushes the mass of the white dwarf above the maximum value it can have.
The maximum mass that a white dwarf can have is…
1.4 solar masses.
Which of the following nuclei has the lowest binding energy per nucleon?
The nucleus of helium.
Which is the heaviest element that can be obtained through nuclear fusion of the lighter ones with a release of energy?
Iron.
True or false? There are hydrogen spectral lines in the spectru Type II supernova.
True.
Which of these fusion reactions in a high-mass star lasts the shortest period of time?
The fusion of silicon into iron.
Why does the core of a high mass star collapse?
Because the iron core’s mass becomes so big that degenerate electrons cannot sustain the pressure and the electrons combine with protons in the nuclei to produce neutrons and neutrinos.
Type II supernova occurs when…
A large mass stars explodes.
Type II supernovae are important because…
The elements heaver than iron are synthesized.
True or false? Most of supernova 1987A energy output (luminosity) was in the form of neutrinos.
True.
Crab nebula is a…
Supernova remnant.
A pulsar is…
A fast spinning neutron star.
What causes the radio pulses of a pulsar?
As the star spins, beams of radiation from it sweep through space. If one of these beams points towards the Earth, we observe a pulse.
True or false? According to General Theory of Relativity, mass/energy curves spacetime.
True.
In order to detect a black hole one looks for…
A binary system where a companion star is not visible but has a mass greater than 3 solar masses and is an intense X-ray source.
Which of these stars spends the longest times as a main sequence star?
0.5 solar mass star.
The current luminosity of the Sun is…
Larger than when it was formed 4.6 billion years ago.
Which of these fusion reactions in a high-mass star creates the most energy per nuclear reaction?
The fusion of hydrogen into helium.
True or false? The pressure of degenerate electrons increases with temperature.
False.
Sirius B is…
A white dwarf.
A star of 5 solar mass fuses hydrogen into helium via…
CNO cycle.
A star of 0.5 solar mass fuses hydrogen into helium via…
Proton-proton chain.
True or false? White dwarfs will stop emitting light in a distant future.
True.
