Nov. 29 – 2B03 29/11/2011 10:27:00 AM
Structure in the universe – output of simulations.
Dark matter dominates mass, and therefore dominates how structure grows.
Dark matter + gravity = structure.
o Galaxies follow dark matter.
Structure – network of nodes, filaments, looks like a big web.
Stellar mass – biggest stars that form, and end of their lives will
become a black hole after they explode in supernovae.
Supermassive - weigh a million (up to a billion) x the mass of the
sun. live in the centre of galaxies.
Intermediate mass – maybe.
o Some evidence – 1 or 2 may have been seen.
o Controvery – how do you get big guys without middle guys?
If you want a black hole, you have to squeeze earth to the size of a marble.
How do supermassive black holes form?
How do we make big ones?
o 1) start w/ stellar mass. Can you get merge them and get a
massive one? Must happen really fast, and must be a whole
lot of them – early history.
o You would expect to see intermediate, we dont though. Hard
to detect yes, but we should have seen by now.
o STILL AN OUTSTANDING BIG QUESTION.
Only biggest stars that become black holes – not that many.
The very first stars that formed - no heavy elements, just H and
HE. Turns out, these are really big. We think very first stars became
o 1 gen – supernova-> black holes. Maybe they merged and
became supermassive black holes.
Supermassive black holes in the centre… Passive vs. Bright.
o We never end up seeing a black khole (traps light). As
material falls in, it gets heated up and radiates energy. Hot
material close to a black hole.
o Not feeding on gas – passive galaxies.
o Feeding on gas - Bright (AGN).
Nucleus of the AGN can be as bright as the whole galaxy.
Some have jets coming out of the centres
Nucleus in centre – rapid variability. Region where light coming
from is small.
Distant universe – filled w/ active galaxies.
o Really common in early universe. Now rare.
Visible across whole universe.
o Most bright things in the universe– galaxies or AGN.
Every few months this is changing. Record is for AGN
Even though its small, it is so energetic that it can affect the
evolution of the whole galaxy, especially those w/ jets.
Actve galaxy – can shut off star formation in the entire galaxy.
AGNs come in types…
THey all have incredible luminosity coming from a small volume.
Different ones – where in the spectrum they are.
Feeding the BH
They are luminous because they are feeding on gas.
Our galaxy has a supermassive black hole.
o We don’t see any bright luminosity – therefore its not active.
Accretion disk – disk around black hole, falling gas.
Our galaxy could be a "starved" SMBH
Gas has already gone into star formation or into the black hole –
not too much left. T