Transcript Properties of Galaxies - UC Berkeley Astronomy Department Home

Spiral Galaxies
Elliptical Galaxies
Irregular Galaxies
Classification of Galaxies
Properties of Galaxies
Spirals
Ellipticals
Irregulars
Mass [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
ephan’s Quintet –
Colliding galaxies
The
“Anntenae”
Galaxies –
a case study
Ring Galaxies – the “splash”
Head-on collisions can produce a “ripple” of star formation that
expands outwards.
Galactic Superwinds
Southern Hemisphere only
The Magellanic
Clouds
These are the nearest
irregular galaxies.
There are others even
closer, being torn apart
by our Galaxy (last
discovery: 2003 in
Canis Major).
Our Immediate Galactic Neighborhood
Members of the Local Group
M31 vs Milky Way
Before the Sun dies, we
may collide and merge
with the Andromeda
Galaxy… (not quite
sure yet about this)
Collisional Aftermath
And outward…
Galaxy Clusters
Virgo
Notice the giant ellipticals at
the centers of many clusters.
These are an example of
“galactic cannibalism”.
Coma
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
The Core of
M87
(at the center
of Virgo)
Giant Radio Lobes
Many such jets are seen. If
they last long enough, they
can blast out of the galaxy
for millions of light years:
the largest single coherent
objects in the universe.
Seyfert
Galaxies
Increasing exposure times….
Some galaxies have
unusually bright
nuclei…
Quasars
(Quasi-stellar Objects)
Star
QSO
Strange “stars” were found with spectral
lines that turned out to be normal lines
but at extremely high red Doppler
shifts. The expansion of the Universe
means that they must be VERY far
away, yet they were not too faint.
Even Seyfert nuclei would not
be bright enough. The energy
output would have to be up to
100’s of times that from a
whole normal galaxy, but the
source was point-like.
Host Galaxies of Quasars
Finally, we were able to obtain deep images of quasars, and show
that indeed they are extremely bright galactic nuclei. The only
power source that is adequate is a supermassive black hole,
eating up to several solar masses per year.
Centaurus A
Supermassive
Black Holes
You know the Milky Way
has a 3 million solar mass
BH at its center. Are they
common? Bigger?
Luminosities seem to require them.
How could we prove the theory?
A billion solar-mass black hole is
still only the size of the solar
system.
Measuring
the
Monster’s
Mass
Images of Active Galaxy disks
Recently, the theory of AGN has received
spectacular visual confirmation from the
Hubble Space Telescope.
Unification of Active Galactic Nuclei
Depending on what the viewing angle is, what we see
can be rather different. This is now sorted out.
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.