JSchreiberTalk3 - FSU High Energy Physics
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Transcript JSchreiberTalk3 - FSU High Energy Physics
Galaxy Formation and
Dark Galaxies
John Schreiber
Outline
Background info (formation/evolution of
galaxies)
Implications of theories
More dwarf galaxies should be observed
These may exist as difficult-to-detect “dark galaxies”
VIRGOHI21
Rotating H cloud in the Virgo cluster
Possible dark galaxy
Discrepancies
Background info
What is a galaxy?
Basic unit of
cosmology
Can contain stars,
gas, dust, dark matter
Formation of Galaxies
Before
As universe expands, density
enhancements either grew or
dispersed.
Smaller, more dense density
enhancements first to
collapse.
These first “lumps” that broke
free contained some H and
He, but mostly dark matter.
Protogalaxies
When this “lump” collapses
under its own gravity
Appear abt. 14 mill. years b.p.
Should be detectable via their
heat signature
Evolution of Galaxies
Star Formation
Clouds of gas orbit in the
protogalaxy
Density of some of these
clouds increases as gas
falls towards the core of the
protogalaxy
Clouds collide
Primeval galaxy
Collision creates a high
density region where a star
cluster forms
Remaining gas heated by
stars (dissipates)
Initial rate of star formation
Slow—cons. ang.
momentum forces a spiral
disk
Fast---elliptoid
Implications of Current Theory
More dwarf galaxies
should exist than
currently observed
May exist as dark
galaxies
Starless clouds of H
and dark matter
Observed via radio
waves (w/ wavelength
of ~ 21 cm)
No dark galaxies
have currently been
discovered
Other possibilities
Galactic cannibalism
Unaccounted for
environmental factor
Little empirical info
about “young galaxies”
VIRGOHI21-Dark Galaxy?
Possible dark galaxy
Rotating cloud in the
Virgo cluster
Contains enough H to
form 100 mill. Sunsized stars
Recently located by a
team led by Robert
Minchin
Used the radiotelescope at the
University of
Manchester
After examining it w/
optical
telescope“confident” it
is a dark galaxy
VIRGOHI21-Other Possibilities?
May not be a dwarf
May be two passing H clouds
Mass from dark matter prevents rotation from tearing
galaxies apart
Measured speed of rotation implies ~1/10 dark matter
of Milky Way
This implies 100x more H should be present
Would give illusion of rotation
Counter-arguments
Few known H clouds
If H gas ionized it would be “invisible to radio
telescopes”
Sources
http://www.newscientist.com/article.ns?id=dn7056
http://abyss.uoregon.edu/~js/ast123/lectures/lec25.html
http://pinot.phys.uvic.ca/~jfn/mywebpage/gxform.html
http://www.oarval.org/galaxfrm.htm
http://hermes.physics.ox.ac.uk/users/Astrophysics/guide
s/universe/galformation.shtml
http://www.absoluteastronomy.com/encyclopedia/G/Ga/
Galaxy_formation_and_evolution.htm
http://www.astro.cf.ac.uk/computing/parallel/gal2/Sbc.ht
ml