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Galaxies
Galaxies
PSC 203PSC 203
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Overview
Overview
In this lecture:In this lecture:
What types of galaxies are there?What types of galaxies are there?
What are the features of each type?What are the features of each type?
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Galaxy types
Galaxy types
How might we categorize galaxies?How might we categorize galaxies?
(what properties could be used to classify
(what properties could be used to classify
galaxies)
galaxies)
SizeSize
Shape
Shape
Brightness
Brightness
…
…
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Hubble’s classification
Hubble’s classification
Hubble came up with a classification basedHubble came up with a classification based
on… on…
ShapeShape
What were his groupings?
What were his groupings?
Spiral / Barred Spiral
Spiral / Barred Spiral
Elliptical
Elliptical
Irregular / Peculiar
Irregular / Peculiar
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Galaxy types Galaxy types
Video
Video , galaxy type overview
, galaxy type overview
video 2, fainter galaxies
video 2, fainter galaxies
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Spiral Galaxies
Spiral Galaxies
Definition …Definition …
a galaxy with a disk in which its brighta galaxy with a disk in which its bright
stars form a spiral patternstars form a spiral pattern
What galaxy have we already seen that is
What galaxy have we already seen that is
a spiral?
a spiral?
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Example Image
Example Image
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Example Image
Example Image
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Structure
same general structure as our galaxy:
disk
bulge
halo
spiral arms
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Two types of spirals
Two types of spirals
Regular spirals
Regular spirals
Barred Spirals
Barred Spirals
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Sizes
Sizes
they range somewhat in sizethey range somewhat in size
Milky Way isMilky Way is
75,000 ly across75,000 ly across
smaller :
smaller :
15,000 ly across15,000 ly across
larger :
larger :
112,500 ly across
112,500 ly across
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Viewing Angle
Viewing Angle
spiral galaxies look very differentspiral galaxies look very different
depending on the angle of the diskdepending on the angle of the disk
““face on”: see top view, whole diskface on”: see top view, whole disk
edge on” see side view, edge of disk
edge on” see side view, edge of disk
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Appearance
Appearance
specks in halo are not stars but entire
specks in halo are not stars but entire
globular clusters
globular clusters
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Example Images
Example Images
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Example Images
Example Images
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Example Images
Example Images
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Irregular Galaxies
Irregular Galaxies
Definition …Definition …
a galaxy lacking a symmetric structurea galaxy lacking a symmetric structure
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Structure
Structure
can take many formscan take many forms
key is irregularity and asymmetrykey is irregularity and asymmetry
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Example Images
Example Images
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Example Images
Example Images
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Irregulars
Irregulars
irregulars may
irregulars may look
look like nebula
like nebula
but they are really much, much largerbut they are really much, much larger
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Peculiar galaxies
Peculiar galaxies
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Interacting Galaxies
Interacting Galaxies
some irregulars form when galaxiessome irregulars form when galaxies
interact interact
gravity of one pulls on the othergravity of one pulls on the other
may even collide
may even collide
end result is galaxy or galaxies with
end result is galaxy or galaxies with
distortions
distortions
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Example Images
Example Images
