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AST test 3
Supernova 1987A, Neutron Stars, Einstein’s Gravity
14
Astronomy
Undergraduate 2
03/31/2011

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Term
Neutron stars
Definition
mass of sun, radius ~ 10km, density like atomic nucleus, huge gravity at surface
Term
pulsars
Definition
rotating magnetized neutron stars
Term
Production of pulses
Definition
probably related to strong electric, magnetic fields at magnetic poles.
Term
X-ray pulsars
Definition
accreted gas channeled to magnetic poles, “pulsar” by lighthouse effect if magnetic axis is tilted with respect to the spin axis
Term
Magnetars
Definition
neutron stars with magnetic fields 100 to 1000 times stronger than the Crab nebula pulsar.
Term
Soft gamma-ray repeaters
Definition
objects that emit intense bursts of low energy gamma rays and X-rays for a
few minutes every few years. Periodic “pulses” after the initial flash. Observed spin-down rates imply
they are magnetars. One soft gamma-ray repeater actually caused aurorae and interfered with terrestrial radio communications August 1998, another flared on the far side of our Galaxy, and was detected on December 27, 2004.
Term
Einstein
Definition
"there is no “force” of gravity. Matter curves space and curved space tells matter how to move."
Term
Dimension
Definition
determined by the number of mutually perpendicular directions in a given space
Term
Parallel propagation
Definition
the process of constructing a straight line; by extending a line segment parallel to itself. Guaranteed to produce the shortest distance between starting, ending points. Works in curved as
well as flat space.
Term
Embedding diagram
Definition
a method of reducing a three (or higher) dimensional space to two-dimensional space that preserves the basic geometry and curvature of the original space. This allows us to “see” the curvature.
Term
Event Horizon
Definition
Since nothing with velocity less than or equal to the speed of light can pass backward through an event horizon, the information that an event occurred cannot pass through, so an event on the
wrong side of an event horizon can never be known to an observer on the opposite side, hence the name.
Term
Singularity
Definition
region in center of black hole where ordinary space and time cannot exist because of severe
space time curvature and quantum uncertainty. The boundary of physics as we currently know it.
Term
Tidal forces
Definition
tend to draw any object into a “noodle” shape for two reasons: the force closer to the center is
stronger and because two separated points the same distance from the hole tend to approach one another
as they both try to fall directly toward the center.
Term
Hyperspace
Definition
space with more dimensions than the one under consideration
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