The Expanding Universe Flashcards
what did 20th century astronomers photograph?
the spectra of galaxies
what did the photos of spectra of galaxies allow astronomers to measure?
Doppler shift, and thus the radial velocity
Vesto Slipher
1912: obtained 1st measurement of Andromeda galaxy
- determined it was moving toward us at 300 km/s
how many galaxies were redshifted (moving away from us)
21 out of 25 galaxies
what did Hubble work to obtain?
distances to the galaxies
what did Hubble use to measure distances to galaxies?
Cepheid variable stars
Hubble’s 1929 Discovery
the further away a galaxy was, the larger the recessional velocity
what two things did Hubble deal with?
recessional velocity and distance
Spectra
the combined light of many stars
what measurement can you get from the spectra of a galaxy?
you can derive the recession velocity
what is the most fundamental method for distance?
stellar parallax
brightness formula
luminosity/4 x pi x d^2
what are 3 standard candles
main sequence stars
cepheid variable stars
type 1a supernovae
type 1a is related to what kind of star
white dwarf
what are cepheid variable stars
pulsating stars that vary in light output
combining brightness and lumin. gives you
the distance
key project for Hubble space telescope
using Cepheids to determine distance to galaxies (w/in 25 Mpc)
what do type 1a supernova result from
detonation of white dwarf stars
when do white dwarf stars detonate
slightly after mass exceeds 1.4 solar masses
Type 1a luminosity
very luminous 9detected at over 1 billion pc)
what can be serve as cosmological probes?
type 1a supernova, since they can be detected from billions of parsecs away
Hubble’s law
relation b/w distance and velocity
Hubble Law formula
v = H x d
what is the Hubble law telling us about the universe?
that it’s expanding
are we in a preferred location in the universe?
NO
Einstein’s cosmological constant
opposes gravity and makes Universe static
George Lemaitre
proposed that the observed recession of galaxies was evidence for the expansion
Big Bang Universe
A universe w/ a well defined beginning
-time where separation of galaxies was very small
Nature of the Expansion of Universe
doesn’t have a center, but rather the “fabric” of space time carrying the galaxies is expanding
If fabric of space/time expands by a factor of two, the distance b/w galaxies will…?
increase by a factor of 2
why are galaxies redshifted?
not due to doppler shift, but due to expansion of space
cosmological redshift
wavelength of light is stretched as Universe expands
redshift
shift of spectral lines to longer wavelengths
redshift formula
z = obs wav - emitted wav/emitted wav
when you measure cosmological redshift, we often express it as…?
a recession velocity
What to use to measure distance to very distant galaxies?
Hubble law
v = H x d
redshift can be used as a measure of what?
distance
what device performed the largest redshift survey of galaxies?
SDSS
Sloan Digital Sky Survey
cosmic web
non uniform distribution of galaxies and galaxy clusters
