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 – Carbon-oxygen 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? Initial conditions when the galaxies formed 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 about 300 million LY in size 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