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Nov. 29 - 2B03.docx

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Department
Astronomy
Course
ASTRON 2B03
Professor
Laura Parker
Semester
Fall

Description
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. Blackholes  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? Hierarchical formation. 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 black holes. 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. Active Galaxies  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 though.  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
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