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NOTES: Characteristics of Galaxies
Classification: The Hubble Tuning Fork
Elliptical: E0--E7 Spheroids, E0 is spherical, E7 least spherical.
Population II stars, little dust, almost no star formation.
Normal Spirals: Sa, Sb, Sc Sa is most tightly wound, Sc least.
Population I stars in disk, Pop. II in nucleus. Dust and star
formation in disk.
Barred Spirals: Sba, Sbb, Sbc Have bars across nucleus, Same
winding rules as normal spirals. Same content as normal.
Irregulars: No definite shape. Ex. Large and small Magellanic
clouds. Dominate universe by number, although generally
smaller. Star formation, but less dust than disks.
Peculiar: (Pec) Have a definite form, but with peculiarities.
Radio jets or other strangeness.
The Hubble Tuning Fork—Classification of Galaxies
Regular and dwarf ellipticals have no dust and
are made up of old Pop. II stars
No dust—no aliens!
Supergiant Ellipticals as in Coma rich cluster
(rich in dust), formed from galactic mergers?
S0 Galaxy in Sextans
(the sextant) no spirals.
M64—the ‘black eye’ galaxy
Sa classification
Irregular galaxies (Irr): about ½ of galaxies are Irr.
Near the Milky Way
Peculiar Galaxies (Pec) have a shape, but a ding.
NGC4631 Pec class spiral galaxy with a ding.
Luminosity class—similar to stars
Fritz Zwicky discovered
dark matter in galactic
clusters in 1930s.
Galactic mass for large spirals can be
Determined from galactic rotation curves.
Which implies the existence of dark matter
(not seen). About half is ordinary (baryonic),
but other half is exotic. WIMPS, etc.?
We can also find mass
from movement in a binary
galaxy system or cluster.
Distance: Standard candles--Cepheids, Supernova
type Ia, standard galaxies like brightest spiral or
Supergiant ellipticals in Cluster cores.
If all else fails, Hubble's Law.
Hubble's Law: v = Ho d.
Velocity from redshift is
proportional to distance.
Hubble’s constant = Ho
= 70 km/s/Mpc (Friedmann
in early ‘1990’s).
Observations of redshift
first done by
Milton Humason,
a janitor at Mt. Wilson
Observatory (working for
Edwin Hubble.
Diameter: from distance and angular diameter.
Diameter = distance times angle (in radians)
How do we get luminosity?
Luminosity: from distance and flux
(or mass and Mass-Luminosity relation
for main sequence stars).
NOTES:
Where are you?
You are here-->
Earth, Solar System, Milky Way Galaxy...
The Local Group: a galaxy 'poor' cluster of 27 galaxies: three
large spirals, 12 dwarf ellipticals, 4 ellipticals, and 8 Irr. Dust
in the plane of the Milky Way may obscure more.
The Local (Virgo) Supercluster: Pancake-shaped. Composed
of the Virgo Cluster (a 'rich' cluster) and about 100 other
clusters including Local Grp. We are falling toward Virgo
Cluster, which has three supergiant ellipticals (M87 contains
accretion disk indicating BH or WH in center--a quadrillion solar masses!)
The Pisces-Cetus Complex: may include 400 rich (and lots of
poor) clusters. Brent Tully. Is the Universe homogeneous?
God's Bubble Bath: Galaxy superclusters seem to from in
bubble structures and filaments with Voids 100-500 million
LY across. Some call this the Cellular Universe.
The Great Wall and The Stick Man--supercluster structures.
The Great Attractor--hidden by Milky Way Dust in Centaurus.
1017 Mo! May be dense giant supercluster with lots of dark
matter. Tens of thousands of galaxies are falling into it,
ignoring the Hubble Flow.
What is your cosmic address?
Earth, Solar System, Milky Way, then…
The local group—our galaxy cluster--a 'poor'
cluster of 27 galaxies: three large spirals, 12 dwarf
ellipticals, 4 ellipticals, and 8 Irr. Dust in the plane
of the Milky Way may obscure more.
Then the Local (or Virgo) Supercluster
The Local (Virgo) Supercluster: Pancake-shaped.
Composed of the Virgo Cluster (a 'rich' cluster)
and about 100 other clusters including Local Grp.
We are falling toward Virgo Cluster, which has three
supergiant ellipticals.
M87 in Virgo contains accretion disk indicating
BH or WH in center--a quadrillion solar masses!
BH is 2 billion solar masses. Accretion disk is
shown on the right.
In core:
An X-ray image of the rich galaxy cluster Abell 2142,
taken with the Chandra Observatory. This cluster is
clearly elongated, and is believed to be the result
of a recent merger between two clusters which have
fallen together along the long axis.
A larger view!
Galaxy superclusters seem to form in bubble
structures and filaments with Voids 100-500 million LY
across. Some call this the Cellular Universe.
God's Bubble Bath: the quantum foam
the universe may have expanded from
minute distortions in space-time.
The Great Attractor —a big lump in the Universe?
Great Attractor: hidden by Milky Way Dust in
Centaurus. 1017 Msun!
May be dense giant supercluster with lots of dark
matter. Tens of thousands of galaxies are falling into
it, ignoring the Hubble Flow. Alan Dressler, Sandy
Faber, and The Seven Samurai from Harvard
discovered it.
At largest scale? Homogeneous?
Yes. Confirmed by observations.