Download Galaxy Evolution

H205
Cosmic Origins
APOD
Today: Galaxy Evolution (Ch. 21)
EP 4 & Reflection 1 due
Find the
Supernova in
Messier 51
• Whirlpool Galaxy
• ~10 Mpc (31 MLY)
• A supernova is an
exploding star
Two Types of Supernovae
• Type II – Massive
stars that run out of
nuclear fuel,
collapse, and explode
• Type Ia – Carbonoxygen white
dwarfs that exceed
the white dwarf
mass limit
What type of SN is SN 1994i
in M51?
Are Type Ia SN
really “standard
candles???”
• Do all Type Ia supernovae
have the same intrinsic
brightness?
• If all arise from CO white
dwarfs that explode at the
white dwarf mass limit,
should they all be the same?
What is the peak magnitude of
SN 1994S?
Galaxy
Evolution:
looking back
through time
• How do we observe the life histories
of galaxies?
• How did galaxies form?
Deep
observations
show us very
distant galaxies
as they were
much earlier in
time
(Old light from
young galaxies)
Why do
galaxies
differ?
a) Initial conditions when the galaxies formed
b) Collisions and mergers
Initial conditions when galaxies formed
• Fast-spinning protogalactic clouds might form
spirals
• Dense protogalactic clouds might cool and
form stars before gas settled into a disk,
producing ellipticals
We must also
consider the
effects of
collisions
• Computer simulation showing the interactions
and eventual merger of galaxies in a compact
group over roughly 4 billion years. (Joshua
Barnes)
http://www.ifa.hawaii.edu/~barnes/groups/vidseq1.mpg
Collisions/Mergers Change
Galaxies
• Distant clusters of
galaxies have a higher
fraction of spirals than
nearby clusters
• Distant clusters
contain more galaxies
within a given volume
• Distant galaxies show
more signs of
disturbance by
neighboring galaxies
(odd shapes, bent arms,
twisted disks)
Many of the galaxies we see at great distances
(and early times) indeed look violently disturbed
Modeling such
collisions on a
computer shows
that two spiral
galaxies can
merge to make an
elliptical
http://www.ifa.hawaii.edu/~barnes/ast110/movies/antennae.mpg
Shells of stars
observed
around some
elliptical
galaxies are
probably the
remains of past
collisions
Evidence for
Galaxy Collisions
• Galaxies are relatively
close together
• Computer simulations
match images of
galaxies
• Ring galaxies
• Starbursts
• Stars not affected
Collisions may
explain why
elliptical
galaxies tend
to be found
where
galaxies are
closer
together
Groups,
Clusters, and
Superclusters
of Galaxies
Coma
Centaurus
Galaxy Clusters
galaxies aren’t the
biggest structures
in the Universe
gravity holds
clusters together
Perseus
Hercules
The Great Wall
of Galaxies
 The largest structure
yet found in the Universe
 280 x 700 million light
years in size
 less than 20 million
light years thick
 diagonally across the
northern sky
 similar structure across
the southern sky
 are they related?
View of
galaxies
obscured
by the disk
of the Milky
Way
Bubbles and Voids
In addition to super clusters
and “walls,” astronomers also
find huge empty regions with
few or no galaxies.
about 300 million LY in size
fossils from the early universe
regions with little or no dark matter?
For Next Week
Chapter 21 – More Galaxy Evolution
EP 5
Delay 2nd Reflection until April 22