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58 Cards in this Set
- Front
- Back
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Neutron stars are made of...
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Type II Supernovae
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what happens before the "core bounce"?
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iron atoms (electrons and protons)in the core are crushed together.
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What is the crushing of electrons and protons known as
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Neutronization
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In the end a neutron star is formed by _____________ pressure of ____________ subatomic particles
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neutron degeneracy pressure; neutrons only
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Neutron Star
-Composition -Mass -Radius -Density |
Neutrons only!
VERY HEAVY VERY SMALL (6 miles wide) ENORMOUS! ( 1 cm3 = Mt everests' weight) |
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At what rate do Neutron stars spin? WHY?
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VERY FAST. b/c
Angular momemtum is conserved |
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What is the equation of angular momentum and how does i explain why neutron stars spin so quickly?
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L(before)= L (after)
mvR (before) = mvR (after) *MASS DOES NOT CHANGE but neutron stars shrink down (radius gets smaller) so rotational velocity must increase! |
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Quantifiably how fast do neutron stars spin?
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Before their collapse they spin once every 25 days after they collapse they make a rotation in less than 1 second.
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Why do Neutron stars have high Magnetic fields?
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Because collapsing stars carry their magnetic fields with them and as the star contracts the field intensifies.
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REVIEW: Neutron stars
-Composition -Mass -Radius -Rotational speed -Density -Magnetic field |
Neutrons
VERY HEAVY VERY SMALL VERY FAST (once it compacts) VERY DENSE HIGH B FIELD (once compact) |
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As a result of all the effects of Neutron stars, what is the unique outcome?
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PULSARS-
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When were pulsars first discovered? how?
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1967, measuring radio signals which showed an unresolved source.
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What causes pulsars?
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Strong magnetic fields at magnetic poles of Neutron stars create HOT SPOTS which beam radiation.
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Do all neutron stars pulsate? do we observe them all pulsating?
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Yes (?);
in order for us to observe a pulsar, 2 things must occur: 1.) the rotational axis and the magnetic axis must BE DIFFERENT. 2.)Earth must be in a position to intercept the radiation from the neutron stars. |
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What is the analogy used with Pulsars?
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Lighthouse search beam. Every time a revolution is made we see a spike in radiation. Followed by rhytmic oscilation.
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How do we know the rotational period of a pulsar?
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By measuring the pulse time and knowing that a pulse can occur 1 time per rotation.
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What is the typical rotational period of a pulsar/neutron star?
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1 to 30 rotations per second.
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The radiation beamed by a pulsar is seen in what area of the spectrum?
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Radio, X-ray, visibile and infared
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What is the youngest known pulsar?
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Crab pulsar which sits in the center of the crab nebula
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Know that PULSARS ARE
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fast rotating highly magnetic Neutron stars!
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What proportion of stars in binarieS?
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more than half are in binaries.
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Recall: what caused Super novas?
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White dwarfs in a binary system
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Neutron star binaries also exist. How is mass exchanged between stars?
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Burning of hydrogen on the surface of the larger star.
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How are neutron star binaries different from Supernova binaries?
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Neutron star binary systems burn much quicklier, hotter and more often.
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Why do neutron stars have more violent binary systems?
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because of much stronger gravitational force.
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What phenomenon is seen as a result of these frequent, quick and hotter eruptions of neutron binary systems?
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X-RAY BURSTERS.
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Where is the source of X-rays that are given off by X-ray bursters?
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The hot acretion disk and "hot spots".
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What "fuels" the bursting? How bright are these bursts in comparison to pulsars?
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FUELED BY FUSION
These bursts are brighter than pulsars bursts. in fact, Earth will recieve the radiation irrespective of its alignment with earth. |
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What is "spin up"?
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When acretion occurs and matter falling into the neutron stars spins faster as it moves closer to the center of the star.
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Does the falling of matter into the star increase the star's rotational period?
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YES! the neutron star can become a millisecond pulsar (rotating thousands of times in a second)
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Gamma ray bursters recieved from space have what flickering of radiation? what does this indicate?
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millisecond flickering; must be from a SMALL EMITTER.
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How do we know the source is small?
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because if the source was large the radiation of that speed would merge together to transverse the object.
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Do gamma ray bursts repeat? Where do they originate?
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NO.
Outside of our galaxy. |
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So Gamma-ray bursts occur in distant galaxies… Why does this make them even more interesting?
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Luminosity greater than 100 supernovae!!!
(more than 100 times brighter than whole galaxies!) OTHERWISE WE WOULDN’T SEE IT FROM EARTH! |
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What are the two theories on how such a luminosity can be produced.
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1.) colliding neutron stars into a close binary
2.)Type II supernova that "in some way" shine their line in only 1 or 2 directions. |
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Can neutron stars be compressed any further?
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YES..... Black holes
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Further pressure from gravity squeezes past the point where neutrons can collapse to form...
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a black hole (> 3 solar masses)
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Black holes are believed to be the remnants/endpoints of...
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stars that exceed 25-30 solar masses on the main sequence and 3 solar masses at its core.
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What is so unique about black holes?
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Because the concentration of mass is so high, gravity is so high that NOTHING CAN ESCAPE A BLACK HOLE! NOT EVEN LIGHT!
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Einstein showed that Newton's laws...
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worked only in "ordinary" situations.
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WHAT ARE THE THREE KEY PREMISES OF EISTEINS THEORY OF RELATIVITY?
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1.) Light always travels at the same speed (c=300,000m/s)
2.) Nothing can travel faster than light 3.)Everything is attracted to gravity (including light) |
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What is the escape velocity of an object?
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V(escape)= sqrt(mass/radius)= sqrt(density)
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The critical radius at which the escape speed equals the speed of light is called the
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Schwarzschild Radius
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The sphere around the Black Hole at the Schwarzschild Radius is called the ___________ because no event inside that sphere can ever be seen, heard or known by anyone outside
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event horizon
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What would happen if the Sun suddenly became a Black Hole?
Would the Earth get sucked in? |
NO! because of the sun's mass it would have a radius of about 3 km. Only objects within 3 km would be sucked in.
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why is it that messages do not get out of black holes?
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Because like all mass in the universe it warps the space. BUT blackholes are so massive that they warp space so much that it actually confines the black hole.
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Stange going-ons near a black hole?
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A person would be stretched then torn apart.
Light becomes redshifted Time slows down |
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Why would her flashlight get redder?
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NOT DOPPLER SHIFT. In fact if she approaches us the light would still be reddened because the effort required to escape gravity causes it to lose energy. (may go into the Infared and even radio waves)
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The fact that her clock stopped is called?
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time dilation
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what would happen to her time at the event horizon
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it would completely STOP!
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Since time slowed what happened to aging...
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One actually ages slower as well.
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What if someone crossed the event horizon?
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Nothing there is no boundary they would just be sucked into the center and crushed into an infentisimally small dot.
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The fact that anything that crosses the event horizon is dragged into the center of the black hole and crushed is called
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Singularity
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How can we see a black hole if it does not allow any light out?
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Because in CLOSE BINARIES we can see matter spiraling into a black hole. As it is being sucked in it is REALLY HOT and RADIATES ENERGY.
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Matter being sucked into a black hole has a unique spectral pattern, what is it?
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X-ray radiation from the center and visibile/infared radiation from the outside.
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Give an example of a black hole?
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Cygnus X-1
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What is the mass of Cygnus 1
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Combined as a binary system, its mass is 35 solar masses.
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Most black holes have been seen by radiation in this part of the spectrum?
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X-ray.
Yet they are NOT x-ray bursters because bursters require accumulation of matter on the surface (not possible in a black hole) |
