Shared Flashcard Set

Details

Astronomy 100
Astronomy Final
57
Astronomy
Undergraduate 2
12/16/2008

Additional Astronomy Flashcards

 


 

Cards

Term

Neutron Star

Definition

-contains about 1 solar mass compressed into a radius of about 10 km.

-high density

-found in the core of a star

Term

What is a pulsar

Definition
a neutron star
Term
Why does a neutron star spin rapidly?
Definition
they spin very fast because it conserves angular momentum as it contracts, and have a powerful magnetic field.   
Term
Why are neutrons hot?  
Definition
the star collapses and the pressure makes it hotter; it’s the core of a star.
Term
Why does it have a strong magnetic field?
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.
Term
How does its density compare to other astronomical objects?
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. 
Term
Why would a pulsar’s spin rate slow with time?
Definition
  It slows as it radiates energy into space. Most of the energy emitted by a pulsar is carried away as a pulsar wind.
Term

How do neutron stars and white dwarfs relate in size?

Definition

Neutron star = muncie

White dwarf = earth

Term
What happens if a neutron star’s mass exceeds about 3 solar masses? 
Definition
If it were more massive than that, it would not be able to support the weight and the object would collapse.
Term
What is the event horizon of a black hole?
Definition
The boundary between the isolated volume of space-time and the rest of the universe.
Term
How is it related to the Schwarzschild radius?
Definition
The radius of the event horizon is called the Schwarzchild radius. It’s the point of no return.
Term
What is a “singularity” as it relates to a black hole?
Definition
 Singularity = infinity; no one knows what is in the center.
Term
Do black holes occur in binary star systems?
Definition
yes
Term
How could we detect a black hole?
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.
Term
  What is an accretion disk?
Definition
Term
What will happen with material that is being gravitationally sucked into a black hole?
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.
Term
How do black holes affect time and space?
Definition
They are interconnected.  Time stops at the event horizon.
Term
What does the escape velocity of an object depend on?
Definition
Mass of the celestial body and the distance from the center of mass to the escaping object.
Term
.  What happens if the escape velocity exceeds the speed of light?
Definition
 Nothing can escape not even light.
Term
What could cause a gamma-ray burst?
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
Term
What is Hubble’s Law?
Definition
Term
What does Hubble’s observation of the redshifts of distant galaxies imply?
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.
Term
How does the Hubble constant relate to an approximate age for the universe? (See also p. 460).
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.
Term

What are the steps to finding the age for a universe?

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
Term
What is unusual about the rotation of the stars in the disk of the Milky Way and in many other galaxies?
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
Term
How does this unexpected property lead to the hypothesis of dark matter?
Definition
Term
What is the current estimate of the age of the universe?
Definition
About 13.7 to 14 billion years old
Term
What evidence led to the big bang model of the universe?
Definition
(Einstein’s theory; Hubble’s data on receding galaxies; cosmic microwave background radiation.)
Term
What are the main elements created during the early phases of the big bang?
Definition
Photons, hydrogen, helium.
Term
How did matter form in the early universe?
Definition
(In matter-antimatter pairs, out of energy)
Term
What happened to the antimatter?
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. 
Term
What is the cosmic microwave background radiation, and how is it related to the big bang theory?
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.
Term
What is Olber’s paradox, and how is it resolved?
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. :[
Term
According to the big bang model of the universe, both the ideas of an edge and a center of the universe are meaningless. 
Definition
we are not at the center of the universe
Term
What’s the current thought on the geometry of the universe?
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.
Term
How is this related to the average density of the universe, and whether the universe is flat, open, or closed?
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.
Term
 Recent evidence suggests that the universe’s expansion rate is accelerating, which leads to what?
Definition

the hypothesis of dark energy

Term
What was the basic idea of the steady state model of the universe?  (Now abandoned)
Definition
The universe looks exactly the same from every spot in it and at every time. No beginning and no end.
Term
What is the cosmic horizon?
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
Term
Are all neutron stars observable from Earth as pulsars?
Definition
No
Term
Are all pulars neutron stars?
Definition
yes
Term
When a pulsar first forms, how fast does it spin?
Definition
nearly 100 times a second
Term
When the pulsar blasts beams of radiation outward what hapens?
Definition
its rotation slows
Term

What is the average age of a pulsar?

What is the oldest detected pulsar?

Definition

average = few million years old

oldest = 10 million years old

Term

What is the difference between young and old neutron stars?

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.
Term
how many pulses come with each sweep?
Definition

two

the first pulse is stronger than the second pulse

Term

What is pulsar wind?

What does the pulsar wind cause?

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

Term

 

Can observers detect a neutron star if it doesn't pass over Earth?

 

Definition

NO

Term
What color should an artist use to paint a neutron star?
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.
Term

When an object collapses what happens?

If an object collapses to zero radius, what happens?

Definition

-it's density increases

-it's density become infinite

Term
If an object has a zero radius what is it called?
Definition
singularity
Term

What is an event horizon?

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)

Supporting users have an ad free experience!