Barred why are some galaxies barred disks are less

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Unformatted text preview: Barred Why are some Galaxies barred? Disks are less stable and prone to bar formation if there is insufficient mass in the centre the The bar may be a response to this, funneling material towards the centre of the galaxy until the bulge is large enough to stabilize the disk enough Forming a bar: bar: Simulation by Chris Mihos Chris Mihos Bars and Dark Halos? Dark Elliptical Galaxies Elliptical Some galaxies are mostly older stars and have no disk have They are a large and small (dwarf) They Elliptical shape – similar to the bulge in spiral similar galaxies galaxies Classified by elongation E0, E1, … E7 E1 E3 E5 Problems of projection Problems Inclination can confuse Ellipicals too Ellipicals One view can be elongated while others look round – we only have one view Detailed orbits can help Detailed E5 view end on? E1 E3 E5 Tweaks to the scheme… Tweaks On close inspection, some Ellipticals Ellipticals have a very faint disk like structure have (often small) (often S0 and SB0 types are intermediates between Spirals and Ellipticals Ellipticals S0 SB0 Irregular Galaxies Irregular Small gas rich galaxies, poorly defined shape Small May be undergoing dramatic star formation May Irr I (distorted spiral), Irr II Irr (distorted Irr Small & Large Magenllanic clouds, Irr I Small Magenllanic clouds, Irr The Magellanic Clouds Magellanic The Milky Way galaxy has two irregular galaxy (Irr I) satellites: The Small and galaxy I) Large Magellanic clouds Magellanic Discovered by Discovered Magellan Magellan 16th C Portuguese Portuguese Explorer Explorer More irregulars More Irr II M82 Starburst! Hubble’s Tuning Fork Hubble The galaxy classification scheme can be arranged as follows: arranged suggestive of some relationships between suggestive of types – Hubble made it up though Do galaxies change types? Do Not in isolation – spirals probably stay spirals spirals, etc… spirals, Colliding galaxies together does change types types Colliding spirals is probably one way to make ellipticals ellipticals Colliding Spirals… Colliding 10 year old Simulation Simulation The Milky Way and Andromeda may collide like this! like The Distribution of Galaxies The To determine the distribution of galaxies in space require distance indicators well beyond the Milky Way indicators As usual, a method is required to determine intrinsic brightness determine Standard candle method compare observed and intrinsic brightness to measure distance measure Tully-Fisher Relation Tully Spiral Galaxies have a brightness in proportion their rotation proportion Rotation can be measured using Doppler shifts for spectral lines Doppler Supernovae Type I Supernovae Type Ia supernova occur due to the Ia supernova explosion of a white dwarf explosion The white dwarf explodes at the critical mass lim...
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