Identify the stages numbered 1-8: nebula white dwarf black dwarf 2. main sequence supernova black hole neutron star planetary nebula 3. red giantred super giant 3.

Galaxy Notes

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Gal·axy- is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter. dark matterdark matter In 1785 William Herschel created this drawing of the Milky Way after hours of counting stars in separate regions of the sky

How Do We Know the Shape of the Milky Way? EM Spectrum MappingEM Spectrum Mapping –1st done with radiowaves –Strength of emission vs. point in sky Studying other spiralsStudying other spirals –amount of gas & dust, and color ViewpointViewpoint –long thin disk vs. a more elliptical silhouette –central bulge Velocities of stars and gasVelocities of stars and gas –show rotational motion

Hubble divided galaxies into three basic types: spiral, elliptical, and irregular.

Spiral Galaxies Hubble divided spiral galaxies into two groups: ordinary spirals and barred spirals.Hubble divided spiral galaxies into two groups: ordinary spirals and barred spirals. Ordinary spirals are designated with an S; barred spirals are designated with an SB.Ordinary spirals are designated with an S; barred spirals are designated with an SB. A barred spiral galaxy is a spiral galaxy in which the spiral arms come from the ends of a bar through the nucleus rather than from the nucleus itself.A barred spiral galaxy is a spiral galaxy in which the spiral arms come from the ends of a bar through the nucleus rather than from the nucleus itself. Courtesy of NOAO/AURA/NSF Fig b: M77 is a type Sb spiral galaxy Figure 17.02c: NGC1365 is a SBc barred spiral galaxy

Elliptical Galaxies Elliptical galaxies are ellipsoids; they are classified from round (E0) to very elongated (E7).Elliptical galaxies are ellipsoids; they are classified from round (E0) to very elongated (E7). Most of the galaxies in existence are ellipticals, but most of these are smaller than spiral galaxies.Most of the galaxies in existence are ellipticals, but most of these are smaller than spiral galaxies. A few giant elliptical galaxies have 2  stars and are thus larger than any spiral galaxy.A few giant elliptical galaxies have 2  stars and are thus larger than any spiral galaxy. Courtesy of NOAO/AURA/NSF Figure 17.04a: NGC5128 (or Centaurus A) is a type E0 peculiar elliptical galaxy.

Irregular Galaxies Fewer than 20% of all galaxies fall in the category of irregulars, and they are all small, normally having fewer than 25% of the number of stars in the Milky Way.Fewer than 20% of all galaxies fall in the category of irregulars, and they are all small, normally having fewer than 25% of the number of stars in the Milky Way. The Large Magellanic Cloud, the nearest galaxy to the Milky Way, is an irregular galaxy. Courtesy of AURA/NOAO/NSE

The Antennae, colliding galaxies Because of their great distances, galaxies exhibit no proper motion. Evidence of past collisions has to come from present appearance. Computer simulations show that colliding galaxies actually pass through one another with few collisions between individual stars. However, large dust and gas clouds in the galaxies make them more likely targets, resulting in increased star formation rates. Collisions between galaxies are not unusual because on average galaxies are separated by distances only about 20 times their diameter. Tidal distortion as a result of a grazing encounter.