Objectives: Explain current theories of how galaxies form, and change over time.

1. Galaxy Formation and Evolution Objectives: Explain current theories of how galaxies form, and change over time. Know the characteristics of the milky way galaxy. Compare and contrast different types of galaxies including; barred, spiral, elptical, and irregular galaxies.

2. Galaxy Formation • Galaxy formation is hypothesized to occur as a result of tiny quantum fluctuations in the aftermath of the Big Bang. • They formed as a consequence of the growth of these primordial fluctuations, which are small changes in the density of the universe in a confined region.

3. Galaxy Formation • The universe was very violent in its early epochs, and galaxies grew quickly, evolving by accretion of smaller mass galaxies. • The result of this process is left imprinted on the distribution of galaxies in the nearby universe.

4. Formation of disk galaxies • commonly called spiral galaxies. • they are very thin, rotate rapidly, and often show spiral structure.

6. merger events in the evolution of galaxies • Our own galaxy has a tiny satellite galaxy (the Sagittarius Dwarf Elliptical Galaxy) which is currently gradually being ripped up and "eaten" by the Milky Way. • It is thought these kinds of events may be quite common in the evolution of large galaxies.

7. Galaxy mergers and the formation of elliptical galaxies • The most massive galaxies in the sky are giant elliptical galaxies. • All elliptical galaxies probed so far have super massive black holes in their center. • In the Local Group, the Milky Way and M31 (the Andromeda Galaxy) are gravitationally bound, and currently approaching each other at high speed. • Astronomers now see elliptical galaxies as some of the most evolved systems in the universe

8. The Milky Way Galaxy • The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. • The very center is marked by an intense radio source which is likely to be a super massive black hole. • The rotational period is about 200 million years at the position of the Sun.The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old

9. The Milky Way Galaxy • The rotational period is about 200 million years at the position of the Sun. • The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. • It is estimated to be about 13.2 billion years old

11. Local Group • The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. • The group comprises more than 54 galaxies, including dwarf galaxies.

12. Spiral galaxies • Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. • These are surrounded by a much fainter halo of stars, many of which reside in globular clusters.

14. Barred Galaxies • A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. • The bar is thought to act as a mechanism that channels gas inwards from the spiral arms, funneling the flow to create new stars.

16. dwarf galaxy • A dwarf galaxy is a small galaxy composed of up to several billion stars.

17. Irregular galaxy • An irregular galaxy is a galaxy that does not have a distinct regular shape. • they are often chaotic in appearance. • Most irregular galaxies were once spiral or elliptical galaxies but were deformed by disorders in gravitational pull

18. Elliptical Galaxies • Appear spherical from all angles, due to the fact that they are not rotating. • They are the oldest and most stable galaxies in the universe.