astronomy ch 22
the radius of a black hole is dependent upon it's...
...mass
observational tests for general relativity
1. mercury's orbit precesses more than Newton's theories predicted 2. eccentric orbit binary stars exhibit same effect, but not as much as general relativity predicts 3. light from background stars passing sun during solar eclipse should be displaced 4. gravitational lensing - bending of light by large masses to form images
special relativity (two postulates)
1. the laws of physics are universal 2. all observers will measure the speed of light to be the same value, regardless of their frame of reference
three ramifications of special relativity
1. time is not an absolute (time passes slower the faster you travel) 2. mass increases with speed 3. length decreases with speed
who discovered pulsars?
Jocelyn Bell
LGM theory
Little Green Men theory, original theory explaining pulsars - believed to be artificial beacons created by aliens because pulses were so precise
why do neutron stars spin so fast?
conservation of angular momentum
ramifications of general relativity
gravity curves space in which it resides, which makes light travel in a curved path
neutron star
incredibly dense core left after a Type II supernova, not actually a star as it can no longer fuse
why does a black hole bend light?
its tremendous gravitational field brutally warps the space around it
how are black holes detected?
like neutron binaries, black holes emit x rays from accretion disk, so just need to find x ray binary with companion greater than 3 masses candidates for this: cygnus X-1 and others
black hole
neutron star greater than three solar masses, cannot withstand this weight, so collapses to a point of infinite density called a singularity - even light can't escape this body
why must a neutron star be composed of particles other than neutrons?
neutron stars have magnetic fields, a magnetic field can only be created by the movement of a charged particle
millisecond pulsars
neutron stars that rotate up to 640 times per second, often found in globular clusters
x ray sources
objects that emit thousands times more energy than our sun, but only at few seconds at a time: occurs much like novae, but emits x rays instead, continues to burst due to continual accumulation of hydrogen some gas doesn't fall directly on neutron star and is emitted as bipolar jetting
glitch
occasional deviance in speed of pulsar
what would happen if you traveled to a black hole
photons from pulsing signals leading us there would be gravitationally redshifted, time would decrease to zero, and gravitational field would rip ship apart
pulsar planets
planet-like bodies detected rotating around neutron stars (still not understood)
Schwarzchild radius/event horizon
point in black hole in which anything that passes can never be seen again
millisecond pulsars in globular clusters problem
problem because globular clusters are old and neutron stars are produced by Type II supernovae from young stars solution: material spirals onto neutron star from a companion star, causing angular momentum and causing rotation
pulsars
rapid, precisely periodic succession of radio pulses, often found in the center of supernova remnants (could be neutron stars)
mu mesons
short-lived particles that come from space, created by cosmic ray photons bombarding upper atmosphere of Earth prove relativity because they have extremely short half-life, yet survive trip to Earth - this is because they travel closet to speed of light so time passes slower for them
why do neutron stars have such a strong magnetic field?
the original magnetic field compressed when the iron core shrunk
why are pulsars likely neutron stars?
theorized that only natural way to produce such regular periods is a small, dense, rotating body (a rotating neutron star)
three types of neutron star binaries
x ray sources, millisecond pulsars, and pulsar planets
general relativity
you cannot tell the difference between acceleration caused by motion and acceleration caused by gravity
