![]() Redshift resulting from Hubble flow is called the The rate at which a galaxy recedes is directly proportional to its distance from us.farthest galaxies are moving away fastest.Hubble discovered this redshift in the 1920's.The light they send us is redshifted when we see it.Galaxies in all directions are moving away from us.Roughly two billion light years from Earth Rich clusters (such as Virgo and Coma) - thousands of galaxiesĭistant rich galaxy cluster, Abell 1689, located.this means there are a relatively small number of galaxies in the Local Group.The Local Cluster is a galaxy "poor" cluster.Large Magellanic Cloud and Small Magellanic Cloud Composition of the Local Group (nearly 50 galaxies).Such a group of galaxies is called a galaxy cluster.These galaxies are bound together by their combined gravity.Major astronomical objects within about 1 Mpc (1,000,000 pc =ģ,300,000 light-years) of the Milky Way Galaxy Nearly 50 galaxies populate the local neighborhood of the Milky Way.rotational velocity (measured by broadening) related to total mass, and therefore, luminosity.determine absolute luminosity of galaxy.works out to 25 Mpc, or so (about 80 million light-years).Current estimate for the number of galaxies in the observable universe:.but nearby, where they are visible, they dominate.they don't show up in the full Universe survey above because of their.The majority of galaxies in the universe are low luminosity, irregular galaxies Types of Galaxies within 30,000,000 light years The galaxies "nearby", where even faint galaxies are visibleĪ survey of galaxies within 30,000,000 light years of the Milky Way reports the following distribution: We can remove the bias against faint galaxies by looking at However, irregular galaxies tend to be small, and not very bright One survey of galaxies in the Universe reports the following distribution:įrom this table it would appear that irregular galaxies are not very Stars and gas have very irregular orbits. Star have random orbits in three dimensions Gas and stars in disk move in circular orbits around the galactic center halo stars have random orbits in three dimensions No significant star formation during the last 10 billion years No obvious structure Irr II galaxies often have "explosive" appearanceĭisks contain both young and old stars halos consist of old stars onlyĭisks contain substantial amounts of gas and dust halos contain little of either No obvious substructure other than a dense central nucleus No disk Stars smoothly distributed through an ellipsoidal volume ranging from nearly spherical (E0) to very flattened (E7) in shape SB galaxies have an elongated central "bar" of stars and gas Highly flattened disk of stars and gas, containing spiral arms and thickening to a central bulge Sa and Sba galaxies have largest bulges, the least obvious spiral structure, and roughly spherical stellar halos. TABLE 24.1 Basic Galaxy Properties by Type Large Magellanic Cloud was the site of the supernova. ![]() Prominent features in the sky in the Southern Hemisphere.Irregular galaxies orbiting the Milky Way Galaxy.rich in interstellar matter and young stars.thin disk and a flattened bulge, but no gas and no spiral arms.S0 and SB0 Galaxies (also known as Lenticular Galaxies) Others E1, E2, E3, E4, E5, E6 (from slightly elongated on up).Shapes range from highly elongated to nearly circular.For example, Milky Way is know to have about 150.Some only thousands of light-year diameters (dwarfs).Some as big as a few million light-year diameter (giant).Recent findings that the bulge of our own Milky Way Galaxy suggest that it is feature elongated "bar " of stellar and interstellar material.Variation of the spiral is the barred-spiral galaxy Size typically 100,000 light year diameter.The American astronomer Edwin Hubble was the first to categorize galaxies in a many turn out to be galaxies, outside the Milky WayĬoma Cluster is one example of a collection of many galaxies, each consisting.Re-examine the catalog of Messier Objects (which was created in the 18th century). ![]()
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