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Sep 20 – 2B03.docx

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McMaster University
Todd Alway

Sep 20 – 2B03 20/09/2011 9:25:00 AM Two main types of galaxies:  Spirals: o Our milky war o Think, disk-like (similar to a frizbee) [2d] o Have spiral arms o Stars are being formed today  Ellopticals o Compared to a frizbee, they are 3d. Similar to a balloon. o Similar, as well, to a cloud of bees.  Within galaxy, stars move around like bees flying about. o Not much rotation and star formation  Most galaxies are one or the other Galxies don’t live in isolation -> they have nearby neighbours.  They live in galaxy grouos. o Feel each other’s gravitational forces.  Our milky way have tiny galaxies orbiting around us, as well as have other large galaxies around us (Andromeda)  Some live in isolation, but most common is in groups Compact (galaxy) groups – distances between galaxies are smaller than galaxies themselves.  Incredibly compact.  Really feeling eachother’s forces. Two spirals colliding (galaxies) -> may create an ellicptical galaxy.  Two ellicptical galaxies colliding will create a larger elliptical.  These are when galxies collidge. Cluster vs group  Different in magnitude : o Group has like 30-50 (no rigid boundary) o Cluster may have like 1000 (much more) Biggest galaxies are the ones in the centre of the cluster (we think it is a result of, over time, colliding and merging with other galaxies) Gravitational lensing -> background galaxies, their light that is, is stretched out by the other galaxies. We will come back to this. Spinning of spiral galaxies – left on its own will stay spiral – the spiral means that it is stable.  When interacted with others galaxies, it will change shape. Galaxy clusters - biggest places in the universe  (Two kinds of clusters:) o Made up of stars, and also made up of galaxies. Most of the mass we see is invisible to the key  Most of the mass of a galaxy is in its dark matter -> invisible. o (we were speaking about the edge of the universe; edge is
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