AST201 midterm Flashcards
who was Fritz Zwicky?
a swiss astronomer that discovered ‘missing mass’ in galaxy clusters during the 1930’s.
who was vera rubin?
an astronomer that observed how stars in the outer reaches of the galaxy moved. she realized that stellar orbital speed increased with distance from center of the galaxy
what was rubin’s original hypothesis, and what was it based on?
according to Newton’s law of gravity, stars should orbit faster closer to the center of the galaxy and slower away. this turned out to be false.
newton’s first law of motion:
objects in motion remain in motion unless acted upon by an external force.
newton’s second law of motion:
the change in speed is equal to the applied force divided by the mass of the object. a=f/m
newton’s third law of motion:
for every applied force, there is an equal and opposite reaction. the ball pushes on you as hard as you push on it.
who is charles bolton?
he studied blue giant star cygnus in 1971, determining it was in a binary orbit with an unseen object of about 155 solar masses. cygnus x-1 was the first widely accepted stellar mass black hole.
the supermassive black hole at the middle of the milky way is
Sagittarius A
what did cecelia payne do?
she used spectrography to find out the composition of the sun
what did edward pickering do?
he created the harvard astronomical computers.
who was williamina fleming?
she was a harvard astronomical computer and created the henry draper catalogue.
who was henrietta swan?
she was a harvard astronomical computer and discovered the cepheid variable star period-luminosity relationship.
who was annie jump cannon?
a harvard astronomical computer that formed the OBAFGKM sequence by analyzing stellar spectra with her own eyes.
what is the OBADGM system called?
morgan keenan system
percentages of the universe:
ordinary matter: 4.9%
dark matter: 26.8%
dark energy: 68.3%
define ‘invariance of light’
the concept that all light rays travel at the same speed, regardless of outside factors, independent of frame of reference.
why is einstein’s theory of special relativity special?
because it only deals with cases where the reference frames move at constant speeds
what is einsteins theory of special relativity?
that all laws of physics are the same in all reference frames that move at constant speeds
if two clocks are synced and one stays on earth and the other is put on an airplane, which will have passed through less time?
the one on the airplane
moving clocks…
run slow
what is relativistic speed?
the speed at which the effects of special relativity can be felt
how many forces?
four
what are the four forces?
electromagnetism, gravity, weak nuclear force, strong nuclear force
electromagnetism:
carrier particle: photon. range: infinite.
strong nuclear force:
carrier particle: gluon
weak nuclear force:
carrier particle: w and z bosons
gravity:
range: infinite. carrier particle: ‘graviton’ ?
what is the acceleration of gravity on earth
9.8m/s
what is einstein’s equivalence principle?
the idea that the laws of physics will work the same in an accelerating frame of reference and in a gravitational field
how did einstein’s theory of general relativity come to be?
he generalized his theory of special relativity to account for accelerating frames of references.
how and what did general relativity replace?
general relativity replaced newton’s concept of gravity with the idea of gravity as a consequence of spacetime curvature instead of a force
define gravitational lensing
where massive objects bend the space around them, forcing light to follow its curved contours
if spacetime is curved by mass, objects…
must follow curved trajectories
how many lines of evidence for the existence of black holes?
five
name all the lines of evidence for the existence of black holes
- xray binary systems
- direct imaging via the event horizon telescope
- gravitational wave measurements of black hole mergers (gravitational wave detectors)
- motion of stars around sag a
- tidal disruption events
define escape speed
the speed required to break free of an objects gravity
define black hole
a region of space where matter is compressed so densely that the escape speed exceeds the speed of light
define event horizon
the outer boundary of a black hole where the escape speed is the speed of light
define singularity
the center point of a black hole, where the density goes into infinity
define Schwarzschild radius
the distance between the singularity and the event horizon
what are the four size ranges of black holes
microscopic, stellar mass, intermediate, supermassive
what is the sun made of
mostly hydrogen, a bit of helium
define spaghettification
the vertical stretching and horizontal compression of objects into long, thin shapes, caused by extreme tidal forces
gravitational time dilation means that
a clock would appear to stop at the event horizon of a black hole
red wavelengths are short or long
long
blue wavelengths are hot or cool
hot
define blackbody
an idealized object that absorbs all wavelengths of light
define spectrograph
something that breaks light from a single material into its component colours
define spectral lines
weaker or stronger regions in an otherwise uniform and continuous spectrum
as the temperature of a blackbody decreases, its wavelength…
increases
the conversion rate of mass to energy is
the speed of light squared (meaning that a small amount of mass produces a huge amount of energy)
define binding energy:
the force that holds things (like nuclei) together
the isolated proton has a mass of
1.00728 AMU
the mass of four combined protons is:
4.00260 AMU
theoretically what should the mass of four protons be? what is the discrepancy?
it should be 4.02912 AMU. there is a 0.7% discrepancy.
protons cannot be bound with the x force and must use the y force
cannot be found with electromagnetism and must be bound by the strong nuclear force
are neutrons bigger or smaller than protons
bigger
neutrinos only interact with which forces
weak nuclear force and gravity, making them ‘ghostly’
define luminosity:
how intrinsically bright something is
define apparent brightness:
how bright something appears to be
apparent vs absolute magnitude
apparent measures apparent brightness, absolute measures luminosity
what is the square inverse law of light
the apparent brightness is simply the luminosity of the star divided by the surface area of the sphere into which it emits light
what does a hertzspring russell diagram measure
surface temperature vs luminosity
the stefan boltzman equation tells us
the relationship between luminosity, temperature, and radius
main sequence stars are called
dwarf stars
what type of star is most numerous in the universe
m class stars, red dwarfs
the masses of stars increase while lifetime…
decreases
stars not on the main sequence no longer…
fuse hydrogen in their cores
the stars above n below the main sequence
above: dying
below: dead
ratio of main sequence stars
one o/b star to every 200 k/m star
how many luminosity classes
5
what are the five luminosity classes in order
supergiants, bright giants, giants, subgiants, main sequence stars
which of the stars in the luminosity classes are alive
only type five
two types of star clusters
open and globular
