February Test Flashcards
Theoretically, the minimum mass of a black hole, formed from the collapse of a dying star's core, is roughly: A) 3 solar masses B) 10 solar masses C) 0.5 solar masses D) 1.4 solar masses
3 solar masses
Where are stars born?
Cold, relatively dense molecular clouds. Named because they are cold enough to molecular hydrogen to form.
What is a protostar?
A compact clump of gas that will eventually become star.
How is a protostar created?
Gravitational contraction of a molecular cloud fragment can create a protostar.
The white dwarf that remains when our Sun has depleted its fuel will be mostly made of: A) carbon B) helium C) hydrogen D) neutrons
Carbon
Summarize the pre-birth stages of a stars life.
1) Protostar assembles from a cloud fragment and is bright in infrared light because gravitational contraction rapidly transforms potential energy into thermal energy.
2) Luminosity decreases as gravitational contraction shrinks protostar’s size
3) Core temperature and rate of fusion gradually rise until energy production through fusion balances the rate at which the protostar radiates energy into space.
What are the major phases of life of a low-mass star?
Main sequence - star generates energy by fusing hydrogen in the core
Red giant - with hydrogen shell-burning around an inert helium core
Helium-core burning and hydrogen shell burning
Planetary nebula - leaving a white dwarf behind
How did past red-giant stars contribute to the existence of life on Earth?
Red giants crested and released much of the carbon that exists in the universe
What prevents carbon from fusing to heavier elements In low mass stars?
Electron degeneracy pressure counteracts the crush of gravity, preventing the core of a low-mass star from ever getting hot enough for fusion
What determines the fate of a stellar core that has exhausted all it’s nuclear fuel?
A star’s final state depends on whether degeneracy pressure can halt the crush of gravity.
What happens if neutron degeneracy pressure cannot halt the collapse?
A neutron star’s core becomes a black hole
What is a white dwarf?
The inert core left over from a low mass star supported by electron degeneracy pressure
Why can’t white dwarfs weigh more than 1.4 times the mass of the Sun?
At masses greater than 1.4, the white dwarf cannot support its own weight with electron degeneracy pressure
What is a nova?
A white dwarf in a binary system can acquire from its companion which soils toward the surface in an accretion disk.
What are white dwarf supernovae (Type Ia) and why are they good for measuring gigantic distances?
They arise from the explosion of an entire white dwarf triggered by carbon fusion when it gains enough mass to approach the 1.4 limit. Because these supernovae have identical light curves, and because they are so bright that they can be seen across the universe, we measure their distances from their apparent brightness in our sky.
What is a neutron star?
A neutron star is the ball of neutrons created by the collapse of the iron core in a massive star supernova.
What is a pulsar?
Pulsars are rotating neutron stars with magnetic fields.
The centre of a black hole is called: A) the accretion disk B) an event horizon C) a stellar core D) a singularity
A singularity
How were neutron stars discovered?
Neutron stars spin rapidly when they’re born and their strong magnetic fields can direct beams of radiation. This beam of radiation was the first sign of evidence.
What can happen to neutron stars in a close binary system?
They can accrete hydrogen from their companions, forming dense, hot accretion disks.
Although it’s impossible, if our sun were to suddenly become a black hole (without losing mass), the Earth would:
A) move close to the black hole
B) experience no changes
C) orbit faster, but at the same distance
D) slowly spiral inwards
Experience no changes
What would it be like to visit a black hole?
1) Time would seem to run slowly for the object
2) Its light would be increasingly redshifted as it approached the black hole
3) The object would never quite reach the event horizon but it would soon disappear from view as it’s light became so redshifted that not instrument could detect it
The Chandrasekhar limit for the maximum mass of a white dwarf is:
A) about three times the mass of our sun
B) about one and a half times the mass of our sun
C) about one-half the mass of our sun
D) about five times the mass of our sun
About one and a half times the mass of our sun
What is a black hole?
A black hole is a place where gravity has crushed matter into oblivion, creating a true hole from which nothing can ever escape, not even light
Do black holes really exist?
No known force can stop the collapse of a stellar corpse with a mass above the neutron star limit of 2 to 3 star masses.
Pulsars are thought to be: A) accreting neutron stars B) accreting white dwarfs C) rotating neutron stars D) unstable high mass stars
Rotating neutron stars
What is the maximum mass of a neutron star?
3Msun
Do black holes suck?
Black holes don’t suck in objects at large distances.
How are high-mass stars different then low-mass stars?
1) they live shorter lives
2) high mass stars die in supernovae, low mass stars die in planetary nebulae
3) high mass stars have convective cores but no other convective layers, low mass stars have convection layers
4) radiation supplies significant pressure support neighing high-mass stars
5) high mass stars can fuse items heavier than carbon
6) a high mass system may leave behind a neutron star or a black hole while low mass stars leave white dwarves
7) high mass stars are less common
What property of a black hole determines it’s “size?”
Depends on its mass because the mass determines the size if the black hole’s Schwarzschild radius
What would happen if you watched someone falling into a black hole?
You’d see time slow down for them as they approached the hole, and their light would be redshifted. They would never reach the event horizon, though they would disappear from view due to their light becoming redshifted.
If we could see the Milky Way from 2 million light years away, it would appear?:
A) to fill the sky with widely spaced stars
B) like a single dim star
C) to be a disk with spiral arms
D) as a faintly glowing, long band of light
To be a disk with spiral arms
If a black Hollie accreting material from a nearby companion binary, the hot gas would best by observed by: A) Arecibo Radio observatory B) IRAS infrared observatory C) Hubble Space telescope D) Chandra X-Ray observatory
Chandra X-Ray Observatory
In the dying stages of our Sun, it will fuse helium into carbon. After that:
A) the carbon will fuse into oxygen and nitrogen
B) the sun becomes a pulsar
C) the core contracts, explodes and fusion of heavier elements for a short period of time
D) the core contracts, but no more fusion occurs
The core contracts, but no more fusion occurs
What causes a supernova?
As a high mass star ages, carbon and heavier elements can fuse to become iron. A fusion of iron uses up energy, an iron core cannot support the wrist of the outer layers and collapses, which results in a supernova that nearly destroys the star
The white dwarf is a/an: A) early stage for neutron stars B) end state for Sun-like stars C) precursor to a black hole D) brown dwarf that has exhausted its fuel
End state for sun like stars
How do high mass stars produce elements heavier than carbon?
High mass stars undergo successive episodes of fusion of ever-heavier elements, producing elements like iron. Elements heavier than that are produced in a supernovae.
Electron degeneracy pressure is the source of pressure that stops the crush of gravity of a: A) black hole B) white dwarf C) terrestrial planet D) neutron star
White dwarf
What did Carl Sagan mean when he said that are all “star stuff”?:
A) that Earth formed at the same time as the sun
B) that the universe contains billions of stars
C) that life would be impossible without energy from the Sun
D) that the sun formed from the interstellar medium
E) that the carbon, oxygen and many elements essential to life were created by nucleosynthesis in stellar
That the carbon, oxygen and many elements essential to life were created by nucleosynthesis in stellar
Where would a brown dwarf be located on an H-R diagram?:
A) upper right
B) on the lower part of the main sequence
C) above and to the the left of the main sequence
D) below and to the right if the lowest part of the main sequence
E) lowest left
Below and to the right of the lowest part of the main sequence
What happens when a star exhausts it’s core hydrogen supply?:
A) its core contracts, but it’s outer lawyers expand and the star becomes bigger and brighter
B) its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness
C) it contracts, becoming smaller and dimmer
D) it contracts, becoming brighter and hotter
E) it expands, becoming bigger but dimmer
Its core contracts, but it’s outer lawyers expand and the star becomes bigger and brighter
At approximately what temperature can helium fusion occur?: A) 100 billion K B) 100,000 K C) 100 million K D) a few million K E) 1 million K
100 million K
Most stars in the Milky Way's halo: A) are very old B) are highly contaminated with carbon C) are very young D) are about the same age as our sun
Are very old
How do we measure the age of a star cluster?
Massive blue stars die first, then white, yellow, orange and red. Main sequence turn off point of a cluster tells us its age.
Which of then following sequences correctly describes the stages of life for a low mass star?:
A) red giant, protostar, main-sequence, white dwarf
B) protostar, main sequence, red giant, white dwarf
C) white dwarf, main sequence, red giant, protostar
D) protostar, red giant, main sequence, white dwarf
E) protostar, main sequence, white dwarf, red giant
Protostar, main-sequence, red giant, white dwarf
What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?:
A) the core contracts and becomes a black hole
B) gravity is not able to overcome neutron degeneracy pressure
C) the star explodes violently, leaving nothing behind
D) the core contracts and becomes a white dwarf
E) the core contracts and becomes a ball of neutrons
The core contracts and becomes a black hole
What do we mean by dimensions?
Each dimension represents an independent direction of possible motion. In 3-D space, the three dimensions of length, width, height are perpendicular to each other. We can’t visual this, but it exists.
After a supernova event, what is left behind?:
A) either a white dwarf or a neutron star
B) always a neutron star
C) always a white dwarf
D) either a neutron star or a black hole
E) always a black hole
Either a neutron star or a black hole
Why is Supernova 1987 A particularly important to astronomers?:
A) it provided the first evidence that supernovae really occur
B) it was the first supernova detected in nearly 400 years
C) it provided the first evidence that neutron stars really exist
D) it occurred only a few dozen light years from Earth
E) it was the nearest supernova detected in nearly 400 years
It was the nearest supernova detected in nearly 400 years
Stars that have the highest concentrations of elements other than hydrogen and helium likely are:
A) recently formed stars
B) formed in molecular clouds
C) the first stars that formed in a galaxy
D) stars found in globular clusters
Recently formed stars
How would an ordinary star, a white dwarf, and a black hole of the same mass differ in spacetime?
Far from the surface they would appear the same. Up close,the white dwarf would distort spacetime more than an ordinary star , and the black hole would distort spacetime so much they it would form a bottomless pit
Although the galactic centre appears relatively calm in the direction of Sagittarius to the naked eye, the motions of gad and stars suggest:
A) it is filled with huge quantities of dust and gas
B) that x-ray binaries are common there
C) a million solar mass black hole is present
D) the galaxy’s spiral arms connect at the very centre
A million solar mass black hole is present
The prevalent cold hydrogen gas within the disk of the Milky Way is most easily observed: A) telescopes made for visible light B) using ultraviolet telescopes C) using infrared telescopes D) using radio telescopes
Using radio telescopes
What is the primary topic of the general theory of relativity?
A theory of gravity, stating they the force of gravity arises from distortions of spacetime
All atoms prominent in biological systems such as nitrogen, carbon and oxygen are:
A) eventually created in planetary nebulas
B) captured by degeneracy pressure
C) released slowly through volcanic eruptions
D) created in high mass stars
Created in high-mass stars
What is spacetime?
The four-dimensional combination of space and time that forms the fabric of our universe.
A typical neutron star will be more massive than the Sun, with a diameter of: A) 20 km B) 2000 km C) 200,000 km D) 200 km
20 km
How have experiments and observations verified the oredictions if the general theory of relativity?
Observations of the change of Mercury’s orbit match that predicted by Einstein’s theory
Observations of stars during eclipses and photos of gravitational lensing provide spectacular confirmation of the idea that light can travel through curved paths
Gravitational redshifted confirm the slowing of time predicted by general relativity
Which element had the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?: A) silicon B) oxygen C) iron D) hydrogen E) uranium
Iron
What is the equivalence principle?
The effects of gravity are equivalent to the effects of acceleration.
About 5 billion years from now, our Sun will become: A) supernova B) nova C) black hole D) red giant
Red giant
How does mass affect spacetime?
Mass causes spacetime to curve, and the curvature of spacetime determines the paths of freely moving masses.
How do we measure the age of a star cluster?
Find the main sequence turnoff point on an H-R diagram. The cluster’ sage is rush to the hydrogen burning lifetime of the hottest, most luminous stars that remain on the main sequence.
What are open clusters?
Contain up to several thousand stars and are found in the disk of the galaxy.
The white dwarf that remains when our Sun has depleted its fuel will be mostly made of:
A) our sun is not in a close binary system
B) our sun is not massive enough for a white dwarf supernova to occur
C) our sun will not become a white dwarf
D) our sun is only massive enough for novae to occur
Our sun is not in a close binary system
What are globular clusters?
Contain hundred of thousands of stars all closely packed together. Mostly found in halo of the galaxy.
Where do you expect to find the youngest stars in the galaxy?
Disk
Where do you expect to find the oldest stars in the galaxy?
Halo
What is the most amount of matter and in the what form?
Dark matter
What lies in the centre of our galaxy?
A gigantic, invisible black hole
A nova can occur if:
A) a white dwarf has a nearby binary companion
B) a neutron star and a nearby companion, forming an x-Ray binary
C) the white dwarf had a strong magnetic field
D) a white dwarf is more than eight times the mass of our sun
A white dwarf has a nearby binary companion
The white dwarf that remains when our Sun has depleted its fuel will be the size of: A) Winnipeg B) Jupiter C) Earth D) Canada
Earth
Planetary nebulae are:
A) planetary atmospheres that extend far from a planet’s surface
B) expanding shells of gas
C) the dust disks that form planets
D) failed stars too cool to maintain fusion
Expanding shells of gas
What does a star become a main-sequence star?:
A) the instant when hydrogen fusion first begins in the star’s core
B) when hydrogen fusion is occurring throughout a star’s interior
C) when the rate of hydrogen fusion within the star’s core is high enough to sustain gravitational equilibrium
D) when a star becomes luminous enough to emit thermal radiation
E) when the protostar assembles from a molecular cloud
When the rate of hydrogen fusion within the star’s core is high enough to sustain gravitational equilibrium
