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Normal Galaxies 15'1 15'2

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Contain flattened disks, central bulges, & spiral arms. Hubble's Classification ... with the size of the bulge. Bulges and halos of spiral galaxies contain ... – PowerPoint PPT presentation

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Title: Normal Galaxies 15'1 15'2


1
Normal Galaxies15.1 15.2
  • By Abby Kirk
  • Christal Mah
  • Christine Johnson
  • Angela Chiu

2
Introduction
  • Edwin Hubble
  • American astronomer who worked on Mt. Wilson in
    California.
  • First to categorize galaxies in a comprehensive
    way.
  • Using his telescope he classified the galaxies
    into four basic types, which is called the Hubble
    classification scheme.

3
Four Basic Types of Galaxies
  • Spirals
  • Barred Spirals
  • Ellipticals
  • Irregulars

4
Spirals
  • Contain flattened disks, central bulges, spiral
    arms
  • Hubbles Classification
  • S denotes a spiral galaxy
  • Classified as type a, b, or c according to the
    size of its central bulge
  • Type Sa ------------? Type Sc
  • decreasing size

5
  • Tightness of the spiral pattern decreases with
    the size of the bulge
  • Bulges and halos of spiral galaxies contain old
    stars
  • Gas and dust-rich disks are where new stars are
    formed

6
Barred-Spirals
  • Main difference it contains a bar of stellar
    and interstellar matter projecting beyond the
    bulge
  • When classifying SB denotes barred spirals
    subdivided into SBa, SBb, and SBc.

7
Ellipticals
  • No spiral arms
  • No galactic disk
  • Dense central nucleus
  • Hubble Classification
  • E denotes Elliptical
  • E0 most circular
  • E1 -----------------------------? E7
  • slightly flattened most elongated

8
?-------- E1
E3 -------?
9
Giant Dwarf Ellipticals
  • Giant Ellipticals
  • Much larger than the Milky Way
  • Trillions of stars
  • Dwarf Ellipticals
  • Fewer than a million stars
  • Most common - outnumber Giants 10 to 1

10
Ellipticals
  • Contain little or no gas or dust
  • All halo no disk, no gas, no dust
  • Made up mostly of old, reddish low-mass stars
  • No evidence of young stars or ongoing star
    formation

11
SO SBO Galaxies
  • SO spiral galaxy with no bar
  • SBO spiral galaxy with bar
  • Look like spirals with no gas and dust just a
    stellar disk

12
?------- SO
SBO ---------gt
13
Irregular Galaxies
  • Cannot be placed into any of the other categories
    based on their visual appearance.
  • Rich in interstellar matter
  • Young blue stars
  • No spiral arms or central bulges

14
  • 2 subclasses
  • Irr I
  • look like misshapen spirals.
  • Irr II
  • rare and often exhibit a distinct explosive
    appearance.
  • Irregular galaxies are smaller then spirals.

15
Collision of two spiral galaxies
16
Distribution of Galaxies in Space
  • Determining Distance
  • Cepheid Variable
  • Standard candles
  • Tully-Fisher Relation
  • Galaxy Clusters
  • Small clusters
  • Large clusters
  • Clusters of Clusters

17
Determining Distance
  • Cepheid Variable Technique
  • Can only be used for nearby galaxies
  • Distant galaxies cannot be observed well enough

18
Determining Distance Further
  • Standard candles
  • Easily recognizable object whose luminosities are
    already determined
  • Those luminosities are used to determine distance
    and luminosity of the objects in question
  • Standard candles must
  • 1) have a narrowly defined luminosity
  • Be bright enough to be seen from far away

19
Determining Distance Further
  • Tully-Fisher Relation
  • Determines a galaxys luminosity by observing how
    fast it rotates
  • A galaxys rotation speed is determined by
    measuring the broadening it causes in its
    spectral lines
  • Can measure spiral galaxies up to 200 Mpc away
  • Tully-Fisher relation and standard candles share
    the 5th rung of the cosmic ladder

20
Galaxy Clusters
  • Small clusters
  • About 20 galaxies populate our Galaxys
    neighborhood called the Local Group
  • Small clusters (like the Local Group) contain
    only a few galaxies and have an irregular shape
  • Large clusters
  • 17 Mpc from our galaxy is the Virgo Cluster,
    which holds 2500 galaxies
  • Large clusters contain 1000s of individual
    galaxies distributed fairly smooth across space

21
SUPERCLUSTERS!
  • Many astronomers believe that there are clusters
    of clusters
  • We call these superclusters

22
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