Term
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Definition
-contains about 1 solar mass compressed into a radius of about 10 km. -high density -found in the core of a star |
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Definition
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| Why does a neutron star spin rapidly? |
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Definition
| they spin very fast because it conserves angular momentum as it contracts, and have a powerful magnetic field. |
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Definition
| the star collapses and the pressure makes it hotter; it’s the core of a star. |
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| Why does it have a strong magnetic field? |
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Definition
| The gas of a normal star is ionized, and that means the magnetic field cannot move easily through the gas. When the star collapses, the magnetic field is carried along with the compressing gas and squeezed into a tiny area, which could make the field a billion times stronger. |
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| How does its density compare to other astronomical objects? |
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Definition
| It has a density of 10^14 g/cm³. On Earth, a sugar cube size of this material would weigh 100 million tons. It’s roughly the size of an atomic nucleus, and can think of a neutron star as matter with all of the empty space squeezed out of it. |
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| Why would a pulsar’s spin rate slow with time? |
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Definition
| It slows as it radiates energy into space. Most of the energy emitted by a pulsar is carried away as a pulsar wind. |
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Term
How do neutron stars and white dwarfs relate in size? |
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Definition
Neutron star = muncie White dwarf = earth |
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Term
| What happens if a neutron star’s mass exceeds about 3 solar masses? |
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Definition
| If it were more massive than that, it would not be able to support the weight and the object would collapse. |
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Term
| What is the event horizon of a black hole? |
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Definition
| The boundary between the isolated volume of space-time and the rest of the universe. |
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Term
| How is it related to the Schwarzschild radius? |
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Definition
| The radius of the event horizon is called the Schwarzchild radius. It’s the point of no return. |
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Term
| What is a “singularity” as it relates to a black hole? |
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Definition
| Singularity = infinity; no one knows what is in the center. |
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Term
| Do black holes occur in binary star systems? |
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Definition
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| How could we detect a black hole? |
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Definition
| Look for binary systems in which mass flows into a compact object and emits X rays. If the mass of the compact object is greater than about 3 solar masses, then the object is presumably a black hole. |
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Term
| What is an accretion disk? |
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Definition
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| What will happen with material that is being gravitationally sucked into a black hole? |
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Definition
| Objects would appear to fall slower as it approached the event horizon (time dilation). To see the objects they would need to be detected at longer and longer wavelengths. The tidal forces would crush the object and stretch it longitudinally long before it reached the event horizon. The friction from such a sever distortion would heat the object to millions of degrees and would emit X rays and gamma rays. |
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| How do black holes affect time and space? |
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Definition
| They are interconnected. Time stops at the event horizon. |
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Term
| What does the escape velocity of an object depend on? |
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Definition
| Mass of the celestial body and the distance from the center of mass to the escaping object. |
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Term
| . What happens if the escape velocity exceeds the speed of light? |
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Definition
| Nothing can escape not even light. |
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Term
| What could cause a gamma-ray burst? |
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Definition
| Black holes and neutron stars at the center of accretion disks can eject powerful beams of radiation and gas. Short gamma ray burst occur when the magnetic field in a magnetar breaks the crust or when orbiting neutron stars merge to form a black hole |
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Term
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Definition
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| What does Hubble’s observation of the redshifts of distant galaxies imply? |
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Definition
| The relationship between apparent velocity of recession and distance. The slope of the line is called the Hubble constant. It is important because astronomers use it as 1)evidence that the universe is expanding and 2) the distance to a galaxy can be found by dividing its apparent velocity of recession by the Hubble constant. |
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| How does the Hubble constant relate to an approximate age for the universe? (See also p. 460). |
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Definition
| Dividing the distance to a galaxy by the apparent velocity with which it recedes tells you the age of the universe, and the Hubble constant simplifies the equation. |
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What are the steps to finding the age for a universe? |
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Definition
| The constant H has km/ per Mpc, which is the velocity by a distance.1/H =distance divided by velocity. To get an age, convert megaparsecs into kilometers and then the distance will cancel out and leave you with an age in seconds. To get years, divide by the number of seconds in a year |
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| What is unusual about the rotation of the stars in the disk of the Milky Way and in many other galaxies? |
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Definition
| The outer parts of the rotation curve do not lower velocities, thus the outermost visible parts of the galaxies do not travel more slowly, revealing that the galaxies contain large amounts of mass outside the radius. There are super massive black holes in the middle of the galaxies |
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| How does this unexpected property lead to the hypothesis of dark matter? |
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Definition
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| What is the current estimate of the age of the universe? |
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Definition
| About 13.7 to 14 billion years old |
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| What evidence led to the big bang model of the universe? |
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Definition
| (Einstein’s theory; Hubble’s data on receding galaxies; cosmic microwave background radiation.) |
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Term
| What are the main elements created during the early phases of the big bang? |
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Definition
| Photons, hydrogen, helium. |
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Term
| How did matter form in the early universe? |
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Definition
| (In matter-antimatter pairs, out of energy) |
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Term
| What happened to the antimatter? |
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Definition
| When antimatter particle meets a normal proton the two particles annihilate each other and convert their mass into energy in the form of two gamma rays. |
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Term
| What is the cosmic microwave background radiation, and how is it related to the big bang theory? |
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Definition
| The black body radiation with a temperature of about 2.73k uniformly spread over the entire sky. It is the light from the big bang freed from the gas at the moment of recombination and redshifted by a factor of 1100. It is strong evidence that the universe began with a big bang. |
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| What is Olber’s paradox, and how is it resolved? |
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Definition
| Asked the question why is the night sky dark? The universe is not infinite and age = finite; if it were, the sky would be bright all of the time and we would die. :[ |
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Term
| According to the big bang model of the universe, both the ideas of an edge and a center of the universe are meaningless. |
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Definition
| we are not at the center of the universe |
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Term
| What’s the current thought on the geometry of the universe? |
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Definition
| Geometry o space and time is critical to understanding cosmology. The universe appears to be isotropic and homogeneous. That is, in its major features, the universe looks the same in all directions and in all locations. |
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Term
| How is this related to the average density of the universe, and whether the universe is flat, open, or closed? |
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Definition
| Whether the universe is open, closed, or flat depends on its density. If the density of the universe is less than the critical density, it is open. If the density is more than the critical density, it closed. If the density equals the critical density, the universe is flat—balanced between open and closed. |
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Term
| Recent evidence suggests that the universe’s expansion rate is accelerating, which leads to what? |
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Definition
the hypothesis of dark energy |
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Term
| What was the basic idea of the steady state model of the universe? (Now abandoned) |
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Definition
| The universe looks exactly the same from every spot in it and at every time. No beginning and no end. |
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Term
| What is the cosmic horizon? |
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Definition
| The horizon. In a static universe the distance in light years to the horizon = age of the universe in years (14ly). Galaxies exist beyond horizon but their light has not had time to reach us |
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Term
| Are all neutron stars observable from Earth as pulsars? |
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Definition
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Term
| Are all pulars neutron stars? |
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Definition
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Term
| When a pulsar first forms, how fast does it spin? |
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Definition
| nearly 100 times a second |
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Term
| When the pulsar blasts beams of radiation outward what hapens? |
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Definition
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Term
What is the average age of a pulsar? What is the oldest detected pulsar? |
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Definition
average = few million years old oldest = 10 million years old |
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Term
What is the difference between young and old neutron stars? |
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Definition
| Young neutrons emit powerful beams of ratiations compared to older neutrons that rotate too slowly and have too little energy to generate detectable rasio beams. |
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Term
| how many pulses come with each sweep? |
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Definition
two the first pulse is stronger than the second pulse |
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Term
What is pulsar wind? What does the pulsar wind cause? |
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Definition
Pulsar wind carries away 99.9% of the energy flowing away from a pulsar star with high-speed atomic particles. -it causes small, high-energy nebulae near a young pulsar |
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Term
Can observers detect a neutron star if it doesn't pass over Earth? |
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Definition
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Term
| What color should an artist use to paint a neutron star? |
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Definition
| Since a neutron star has a temperature of a million degrees, the surface emits mostly electromagnetic raiation at x-ray wavelengths meaning it would look blue-white to your eyes. |
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Term
When an object collapses what happens? If an object collapses to zero radius, what happens? |
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Definition
-it's density increases -it's density become infinite |
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Term
| If an object has a zero radius what is it called? |
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Definition
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Term
What is an event horizon? |
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Definition
the boundary between the isolated colume of space-time and the rest of the universe. (the radiuus of an event horizon is called the Schwarzschild radius, Rs) |
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