Chapter 17Early ObservationsTypes of GalaxiesTypes of GalaxiesDistance to Galaxies: Hubble’s LawHubble’s Law is not perfectWhich type of galaxy is the Milky Way?Which of the following best describes Hubble’s LawGalaxy Interactions and EvolutionDifferences in Stellar and Gas ContentCollisions and MergersActive GalaxiesQuasarsA Unified Model of Active GalaxiesQuasar Absorption LinesSlide 16Which of the following is true about galaxy types?Do galaxies transition between types?We don’t see any quasars near us. What does this imply?Slide 20Galaxy ClustersRelationships between Cluster Size and Galaxy TypeSuperclustersSuperclustersWhat are the regions where galaxies cluster together called?Measuring a Galaxy’s MassDark Matter in Galaxy HaloesWhat is Dark Matter? 2 Hypotheses.Slide 29Slide 30Slide 31Dark matter is most likely…Slide 33Chapter 17GalaxiesEarly Observations•Andromeda (M31) seen by 10th century Persian astronomers.•Charles Messier looking for comets in 18th century (“Messier number”)•Sir William Herschel and the “New General Catalog” in the 19th century•1920 - Everyone finally on the same page.Types of Galaxies•Classified by Edwin Hubble (not my cat)•Spiral (S), Elliptical (E), Irregular (Irr)Types of Galaxies•2 special types of spiral galaxies: barred spirals and S0Distance to Galaxies: Hubble’s Law•Such large distances that parallax is useless. Can use method of “standard candles”•Red-shifted spectra tell us they’re moving away from us, but this isn’t the whole story•Dimmer (further) galaxies more redshifted. •Hubble’s Law: V = H*dHubble’s Law is not perfect•Redshift can come from expansion of space AND from motion of galaxies.•Especially in systems of galaxiesWhich type of galaxy is the Milky Way?A. Un-barred SpiralB. Barred SpiralC. EllipticalD. IrregularWhich of the following best describes Hubble’s LawA. An unbreakable law that is always trueB. A law that scientists once thought was true, but has since been discreditedC. Correct for the most part, but with some limitationsGalaxy Interactions and Evolution•Bars in spirals may come and go.•Irregular galaxies come in two types.•“Starburst galaxies”Differences in Stellar and Gas Content•Spiral galaxies have both Pop I and Pop II stars.•Elliptical galaxies have only Pop II stars.•Galaxies with neighbors less likely to be spirals.•Wide range of size for each type of galaxy.Collisions and Mergers•Hubble Deep Field: Look back in time•Smaller and more numerous galaxies back then•“Galactic cannibalism”•Ellipticals lost their gas somehow, but could gain it again and become spirals.•Red sequence and blue sequence.Active Galaxies•Unusually large amounts of energy from a tiny region at their core.•10% of galaxies are active. It may be a “phase”•“Active galactic nuclei”•“Seyfert galaxies” and “Radio galaxies”Quasars•“Quasi-stellar radio source”•Look like dim stars, but are very bright at radio wavelengths.•Extremely distant active galaxies, fluctuate in brightness.•Can determine size of core from variations in brightness.•Don’t see any quasars close to us.A Unified Model of Active Galaxies•Need to explain large luminosity from a small volume, as well as the various types of active galaxies•Super-massive black holes in the core•Large magnetic fields direct the jets•Mass of black hole and mass of bulge relatedQuasar Absorption LinesWhich of the following is correct about elliptical and spiral galaxies?A. Elliptical and spiral galaxies BOTH have Pop I AND Pop II starsB. Spiral galaxies have both populations, but elliptical galaxies only have Pop IC. Spiral galaxies have both populations, but elliptical galaxies only have Pop IID. Elliptical galaxies have both populations, but spiral galaxies only have Pop IE. Elliptical galaxies have both populations, but spiral galaxies only have Pop IIWhich of the following is true about galaxy types?A. Elliptical galaxies are smaller than spiral galaxiesB. Spiral galaxies are smaller than elliptical galaxiesC. Both types of galaxy are always the same sizeD. Both spiral and elliptical galaxies can be large or smallDo galaxies transition between types?A. No. Galaxies never change type.B. Kind of. Elliptical galaxies can become spiral galaxies, but not the other way aroundC. Kind of. Spiral galaxies can become elliptical galaxies, but not the other way aroundD. Yes. Spirals can become ellipticals, and ellipticals can become spiralsWe don’t see any quasars near us. What does this imply?A. Quasars just didn’t form in the Milky WayB. There are still quasars nearby, they’re just hidingC. Quasars only formed in the early universeWhat makes an active galaxy so active? (What is the CAUSE of an active galaxy)A. Black hole at the centerB. High levels of star formationC. QuasarsD. MasersGalaxy Clusters•Ours is called the “Local Group” (so creative)•Local group has more than 40 members, but only three large spiral galaxies.•Dwarf galaxiesRelationships between Cluster Size and Galaxy Type•More galaxies —> more elliptical and S0 galaxies•Large clusters also have large amounts of hot gas•Clusters grow in a similar way as galaxies themselves.Superclusters•A cluster of clusters. Ours is the “Virgo Supercluster”•Only loosely bound togetherSuperclusters•“Filaments” and “voids” are what we see.•This is matched by computer simulations, but only those that include dark matter.What are the regions where galaxies cluster together called?A. FilamentsB. VoidsC. Local GroupD. Deep FieldMeasuring a Galaxy’s Mass•Modified form of Kepler’s 3rd Law•Speed (from Doppler) + size of orbit —> mass•Calculated mass is waaaay bigger than observable mass•Must be something that exerts gravity (has mass) and can’t be seen. DARK MATTER.Dark Matter in Galaxy HaloesWhat is Dark Matter? 2 Hypotheses.•MACHO•Massive compact halo object•Not well-supported•Can only account for 10% of halo mass•WIMPs•Weakly-interacting massive particles•Particles “only” interact via gravity•Gravitational lensing helps to provide supportBased on rotation curves, where must dark matter be located in the Milky Way?A. In the galactic coreB. In the haloC. Evenly distributed throughout the galaxyD. The Milky Way has no dark matterWhat is it called when regions of high gravity bend the path of light?A. Gravitational RedshifB. Doppler ShifC. Gravitational