Allison Thompson Chapter 15 Notes

Chapter 15


What are the three major types of galaxies?
-Our deepest images of the universe show a great variety of galaxies some of them billions of light years away.
-A galaxies age its distance and the age of the universe are all closely related.
-The study of galaxies is thus intimately connected with cosmology. The study of structure and evolution of the universe
-Disk component are stars of all ages many glass clouds.
-Spheroid component bulge and halo old stars few gas clouds.
-Barred spiral galaxy has a band of stars across the bulge.
-Lenticular galaxy has a disk like spiral galaxy but much less dusty gas intermediate between spiral and elliptical.
-Elliptical all spheriodal component virtually no disk component.
-Irregular neither spiral nor elliptical. Blue white color indicates ongoing star formation.

How are galaxies grouped together?
-Spiral galaxies are often found in group galaxies.
-Elliptical galaxies are Much more common in huge clusters of galaxies.

15.2
How do were measure the distance to galaxies?
-Brightness alone does not provide enough info to measure distance.
-Step one is to determine size of solar system using radar.
-Step two is to determines distance of star out to a few hundred light years using parallax.
-Step three is apparent brightness of stars cluster's main sequence tells us its distance.
-Step five apparent brightness of a white dwarf supernova tells us the distance to its galaxy
-Luminosity passing through each sphere is the same.
-Divide luminosity by area to get brightness.
-The relationship between brightness and luminosity depends on distance.
-We can determine a stars distance if were know its luminosity .
-Knowing a star cluster distance were can determine the luminosity of each type of star within.
-Cepheid variable stars are very luminous
-The light curve of this Cepheid variable stars show that its brightness alternately rises and falls over 50 day period.
-Cephied variable stars with longer periods have greater luminosity.
-White dwarf supernova can also be used as standard candles.

What is Hubble's law?
-Before Hubble some scientist argued that spiral nebula were entire galaxies like our Milky Way whereas other scientist maintained They were smaller.
-Hubble settled the debate by measuring the distance to the Andromeda Galaxy using Cepheid variables as standard candles.
-Hubble also knew that the spectral features of virtually all galaxies are red shifted They all move far away from us.
-By measuring distance to galaxies Hubble found the red shift and distance are related in a special way.
-Distance of the farthest galaxies are measured from red shifts.
-We measure galaxy distance using a chain of interdependent techniques.

How do distance measure tell us the age of the universe?
-Hubble’s constant tells us the age if the universe
-the expansion rate appears tone the same everywhere in space
-one example of something that expands but has no center is  a balloon.
-Matter is evenly distributed.
-No center or edge
-Distance between faraway galaxies change while light travels.
-Astronomers think in terms of look back time.
-Expansions stretches photon wavelengths causing a cosmological red shift directly related to look back time.

15.3
How do were observe the life histories of galaxies?
-Deep in observation show us distant galaxies.

How did galaxies form?
-Matter originally file all of the space almost uniformly.
-Gravity of denser region pulled in surrounding matter.
-Denser regions contracted forming progoalatic clouds.
-H and He gases in these clouds formed first.
-Supernova explosions from the first stars kept Much of the gas from forming stars.
-Left over gas settles.

Why do galaxies differ?
-Spin is the initial angular momentum if protogalatic cloud could
-Density creates elliptical.
-Observation of distant red elliptical galaxies support the idea that most
-We must also consider the effects of collisions.
-Collisions were Much more likely nearly in time.
-Many if the galaxies were see at a great distance do indeed looked disturbed.
-The collisions were observe nearby trigger burst of star formations.
-Models such as collisions on a computer show that two spiral galaxies can merge to make an elliptical.
-Collisions may explain Why elliptical galaxies tend to be found where galaxies are closer together.
-Giant elliptical galaxies at the center of cluster seem ton have consumed a number of smaller galaxies.
-Starburst galaxies are forming stars so quickly that They will
-The intensity of supernova explosions in starburst galaxies can drive galactic winds
-The intensity of supernova explosions in starburst galaxies can drive galactic winds.

15.4
What are quasars?
-If the center of the galaxy is unusually bright were call it active galactic nucleus.
-High shifted spectra of quasars indicate large distances
-From brightness to distance
-Variability show that all this energy comes from ra region smaller then solar system.
-Galaxies around quasars sometimes appear disturbed by collisions
-Quasars powerfully radiate energy over a very wide range of wavelength indicating that They contain matter with a wide range of temperature.-Radio galaxies contain active nuclei shooting out vast jets of plasma which edit radio waves coming from electrons moving at near light speed.
-Lobes of radio galaxies can extend .