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Galactic Structure

Galactic Structure. Motion of the Stars. The gravity of stars in the galaxy causes stars to move. This motion can be separated into two parts: Radial motion is motion towards or away from the Earth. Transverse motion moves across the path from the Earth. Sun & Earth. observed star.

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Galactic Structure

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  1. Galactic Structure

  2. Motion of the Stars • The gravity of stars in the galaxy causes stars to move. • This motion can be separated into two parts: • Radial motion is motion towards or away from the Earth. • Transverse motion moves across the path from the Earth. Sun & Earth observed star radial motion transverse motion actual motion

  3. Proper motion measures a star’s position after adjusting for the Earth’s motion around the Sun. Combine with distance Used to find transverse motion Doppler shift is used to find the radial motion. Proper Motion Barnard’s Star is close to Earth

  4. Some stars appear to move away from a common point. Past explosion 53 Arietis, AE Aurigae, and Mu Columbae would all be in the area of the Orion Nebula about 3 million years ago. AE Aurigae 53 Arietis Mu Columbae Runaway Stars

  5. Populations • Stars are segregated by color in other galaxies. • disk stars more blue – population I • halo stars more red – population II • Similar segregation is present in clusters in the Milky Way. sun side view

  6. Type I Clusters Open clusters Hot young stars Lots of gas and dust Abundant in heavy elements Active star formation Type II Clusters Globular clusters Old red stars No gas and dust No heavy elements, just hydrogen and helium No star formation, just old stars Cluster Types

  7. Galactic Motion • Gravity applies to stars in the galaxy. • The motion of the globular clusters indicates the center. • The stars in the disk also orbit the center. • Sun orbits in 230 million years

  8. Fountains • Inside the Milky Way there are areas moving into and out of the disk. • Clusters pass through the disk • Stars and black holes

  9. Galaxy Formation • Like stars, galaxies start with gas. • First formation about 13 billion years ago • Gravity pulled small gas clouds together—with enough density, stars form. • Galaxies merged to form the Milky Way

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