Pulsars are NEUTRON STARS whose
MAGNETIC POLES rotate past us -- "lighthouse" model
TRUE or FALSE: All pulsars are neutron stars,
but not all neutron stars are pulsars.
C. Black Holes
- Beyond 3 Msun, even
NEUTRON DEGENERACY cannot balance gravity
- So object collapses into BLACK HOLE --
not merely "very dense," but INFINITELY DENSE!
- beyond EVENT HORIZON, nothing can escape --
but crossing it would be uneventful!
- falling into black hole would be deadly
- if HOT INFALLING material didn't kill you...
- ...TIDAL FORCES would!
- black hole candidates, from APOD --
- our galactic center*
- M87*
- M84*
D. Galaxies -- Our Own, and Others
- the Milky Way -- our galaxy
- Other Galaxies
- 3 basic types: ELLIPTICAL, SPIRAL
(BARRED)*, IRREGULAR
- structures:
- Some of our nearest neighbors are:
- the nearest large spiral is __________________
- the nearest galaxies are __________________________
- HUBBLE'S LAW
Q: When we look at faraway galaxies,
their spectral lines are red shifted to the red. Why?
E. General Relativity
Recall that our Earth orbits the Sun,
which orbits the Milky Way's center,
which orbits the Local Group's center,
which orbits the virgo Supercluster's center.
Q: How come we don't feel the fact that
we're moving so fast?*
A: _______________________________ and
_______________________________
- Einstein's EQUIVALENCE PRINCIPLE:
No way to tell if gravity pulls or if
spacetime is deformed.
- Mass DEFORMS spacetime:
- like a rock causes a depression in a trampoline!
- (spacetime is 3 spatial dimensions & time)
- falling objects don't "feel gravity",
they move in SHORTEST PATH along DEFORMED spacetime
-- NOT STRAIGHT LINES
Q: When an object does not move in
a straight line, what do we say is happening to it?
A: ___________________________________
- we can therefore restate EQUIVALENCE PRINCIPLE:
GRAVITATIONAL MASS = INERTIAL MASS
- CONFIRMATION of relativity theory:
gravity redirects light, too!
- Eddington's eclipse measurement
- "Einstein Rings" -- mass focuses images, e.g.,
APOD's gravitational lenses*
(also TIME DILATION, but this is boring!)
- Q: Why are BLACK HOLES black?
A: Black hole's mass bends spacetime so much light just runs in circles around the star!