Date post: | 21-Dec-2015 |
Category: |
Documents |
View: | 229 times |
Download: | 2 times |
Spiral Galaxies
Elliptical Galaxies
Irregular Galaxies
Classification of Galaxies
Properties of Galaxies
Spirals Ellipticals IrregularsMass [typical; range]
(solar masses)
1011 ;
109 - 1012
1011.5 ;
106 - 1013
1010 ;
108 - 1011
Size (pc) 104- 105.5 104- 106 103- 105
Color Blue arms,
reddish bulge
reddish bluish
Luminosity 108 - 1010 105 - 1011 107- 109
Stellar Populations Pops I & II Pop II Pop I (Pop II)
Interstellar medium Yes Very little Still some
Rotation Yes (disk) no Not a lot
Fraction 30% 20% 50%
Other galaxy types : Peculiar, Interacting, Ring, Starburst, Dwarf,Luminous Infrared, Active Nuclei, Damped Lyman-alpha
Stephan’s Quintet – Colliding galaxies
The “Anntenae” Galaxies – a case study
Galactic Train Wrecks
Collisional Aftermath
Ring Galaxies – the “splash”
Head-on collisions can produce a “ripple” of star formation that expands outwards.
Galactic Superwinds
The Magellanic
Clouds
Large Magellanic Cloud Small Magellanic Cloud
Southern Hemisphere only
The Galactic Neighborhood
The “Local
Group” of Galaxies
Members of the Local Group
And outward…
Galaxy Clusters
Virgo
Coma
Notice the giant ellipticals at the centers of many clusters.These are an example of “galactic cannibalism”.
Galactic Cannibals – Central CD Ellipticals
At the heart of rich clusters, galaxies pass through the center and are disrupted and collected.
Making a CD galaxy
into the Universe…
Large Scale Structure
On the largest scales (100 million ly) the Universe takes on a “foamy” appearance, with great filaments and walls of galaxies and clusters, surrounding great “voids” that are relatively empty.
Dark Matter - rotation curvesRotation curves imply the mass-to-light ratios of galaxies go up as we look on larger scales: Sun M/L=1, solar neighborhood M/L=3, galaxy M/L=50
Dark Matter – cluster speeds
galaxy clusters M/L=200-500
From average speed of galaxies – the cluster would fly apart
From X-ray gas held in – several million degrees and extensive
What could the dark matter be?
1) Normal but dark matter (“baryonic”) : rocks, white or brown dwarfs?
2) Black holes or neutron stars? Too much metals would have been produced.
Anyway, there is a fundamental reason from the Big Bang this can’t be it…
Dark Matter :gravitational
lensing The mass required to produce the observed lensing is much higher than the luminous mass. This is a direct observation of gravity due to dark matter.
WIMPS and Cold Dark MatterCould dark matter be some kind of new particles which
interact very weakly with matter (like neutrinos do) but massive, and not moving relativistically? Experiments at Berkeley and elsewhere are looking for them (guaranteed Nobel prize!).